zram: free meta table in zram_meta_free

From: Ganesh Mahendran <[email protected]>

zram_meta_alloc() and zram_meta_free() are a pair.
In zram_meta_alloc(), meta table is allocated. So it it better to free it in zram_meta_free().

---
 drivers/block/zram/zram_drv.c | 30 ++++++++++++++----------------
 drivers/block/zram/zram_drv.h |  1 +
 2 files changed, 15 insertions(+), 16 deletions(-)

index 9250b3f54a8f..a598ada817f0 100644
@@ -309,6 +309,18 @@ static inline int valid_io_request(struct zram *zram,
 
 static void zram_meta_free(struct zram_meta *meta)
 {
+	size_t index;
+
+	/* Free all pages that are still in this zram device */
+	for (index = 0; index < meta->num_pages; index++) {
+		unsigned long handle = meta->table[index].handle;
+
+		if (!handle)
+			continue;
+
+		zs_free(meta->mem_pool, handle);
+	}
+
 	zs_destroy_pool(meta->mem_pool);
 	vfree(meta->table);
 	kfree(meta);

@@ -316,15 +328,14 @@ static void zram_meta_free(struct zram_meta *meta)
 
 static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
 {
-	size_t num_pages;
 	char pool_name[8];
 	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
 
 	if (!meta)
 		return NULL;
 
-	num_pages = disksize >> PAGE_SHIFT;
-	meta->table = vzalloc(num_pages * sizeof(*meta->table));
+	meta->num_pages = disksize >> PAGE_SHIFT;
+	meta->table = vzalloc(meta->num_pages * sizeof(*meta->table));
 	if (!meta->table) {
 		pr_err("Error allocating zram address table\n");
 		goto out_error;

@@ -706,9 +717,6 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 
 static void zram_reset_device(struct zram *zram, bool reset_capacity)
 {
-	size_t index;
-	struct zram_meta *meta;
-
 	down_write(&zram->init_lock);
 
 	zram->limit_pages = 0;

@@ -718,16 +726,6 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 		return;
 	}
 
-	meta = zram->meta;
-	/* Free all pages that are still in this zram device */
-	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
-		unsigned long handle = meta->table[index].handle;
-		if (!handle)
-			continue;
-
-		zs_free(meta->mem_pool, handle);
-	}
-
 	zcomp_destroy(zram->comp);
 	zram->max_comp_streams = 1;
 

index b05a816b09ac..e492f6bf11f1 100644
@@ -96,6 +96,7 @@ struct zram_stats {
 struct zram_meta {
 	struct zram_table_entry *table;
 	struct zs_pool *mem_pool;
+	size_t num_pages;
 };
 
 struct zram {

1.9.1

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Admin could reset zram during I/O operation going on so we have used zram->init_lock as read-side lock in I/O path to prevent sudden zram meta freeing.

However, the init_lock is really troublesome.
We can't do call zram_meta_alloc under init_lock due to lockdep splat because zram_rw_page is one of the function under reclaim path and hold it as read_lock while other places in process context hold it as write_lock. So, we have used allocation out of the lock to avoid lockdep warn but it's not good for readability and fainally, I met another lockdep splat between init_lock and cpu_hotpulug from kmem_cache_destroy during wokring zsmalloc compaction. :(

Yes, the ideal is to remove horrible init_lock of zram in rw path. This patch removes it in rw path and instead, put init_done bool variable to check initialization done with smp_[wmb|rmb] and srcu_[un]read_lock to prevent sudden zram meta freeing during I/O operation.

---
 drivers/block/zram/zram_drv.c | 85 +++++++++++++++++++++++++++++++------------
 drivers/block/zram/zram_drv.h |  5 +++
 2 files changed, 66 insertions(+), 24 deletions(-)

index a598ada817f0..b33add453027 100644
@@ -32,6 +32,7 @@
 #include <linux/string.h>
 #include <linux/vmalloc.h>
 #include <linux/err.h>
+#include <linux/srcu.h>
 
 #include "zram_drv.h"
 

@@ -53,9 +54,31 @@ static ssize_t name##_show(struct device *d,		\
 }									\
 static DEVICE_ATTR_RO(name);
 
-static inline int init_done(struct zram *zram)
+static inline bool init_done(struct zram *zram)
 {
-	return zram->meta != NULL;
+	/*
+	 * init_done can be used without holding zram->init_lock in
+	 * read/write handler(ie, zram_make_request) but we should make sure
+	 * that zram->init_done should set up after meta initialization is
+	 * done. Look at setup_init_done.
+	 */
+	bool ret = zram->init_done;
+
+	if (ret)
+		smp_rmb(); /* pair with setup_init_done */
+
+	return ret;
+}
+
+static inline void setup_init_done(struct zram *zram, bool flag)
+{
+	/*
+	 * Store operation of struct zram fields should complete
+	 * before zram->init_done set up because zram_bvec_rw
+	 * doesn't hold an zram->init_lock.
+	 */
+	smp_wmb();
+	zram->init_done = flag;
 }
 
 static inline struct zram *dev_to_zram(struct device *dev)

@@ -326,6 +349,10 @@ static void zram_meta_free(struct zram_meta *meta)
 	kfree(meta);
 }
 
+static void rcu_zram_do_nothing(struct rcu_head *unused)
+{
+}
+
 static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
 {
 	char pool_name[8];

@@ -726,11 +753,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 		return;
 	}
 
-	zcomp_destroy(zram->comp);
 	zram->max_comp_streams = 1;
 
-	zram_meta_free(zram->meta);
-	zram->meta = NULL;
 	/* Reset stats */
 	memset(&zram->stats, 0, sizeof(zram->stats));
 

@@ -738,8 +762,12 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 	if (reset_capacity)
 		set_capacity(zram->disk, 0);
 
+	setup_init_done(zram, false);
+	call_srcu(&zram->srcu, &zram->rcu, rcu_zram_do_nothing);
+	synchronize_srcu(&zram->srcu);
+	zram_meta_free(zram->meta);
+	zcomp_destroy(zram->comp);
 	up_write(&zram->init_lock);
-
 	/*
 	 * Revalidate disk out of the init_lock to avoid lockdep splat.
 	 * It's okay because disk's capacity is protected by init_lock

@@ -762,10 +790,19 @@ static ssize_t disksize_store(struct device *dev,
 	if (!disksize)
 		return -EINVAL;
 
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		pr_info("Cannot change disksize for initialized device\n");
+		up_write(&zram->init_lock);
+		return -EBUSY;
+	}
+
 	disksize = PAGE_ALIGN(disksize);
 	meta = zram_meta_alloc(zram->disk->first_minor, disksize);
-	if (!meta)
+	if (!meta) {
+		up_write(&zram->init_lock);
 		return -ENOMEM;
+	}
 
 	comp = zcomp_create(zram->compressor, zram->max_comp_streams);
 	if (IS_ERR(comp)) {

@@ -775,17 +812,11 @@ static ssize_t disksize_store(struct device *dev,
 		goto out_free_meta;
 	}
 
-	down_write(&zram->init_lock);
-	if (init_done(zram)) {
-		pr_info("Cannot change disksize for initialized device\n");
-		err = -EBUSY;
-		goto out_destroy_comp;
-	}
-
 	zram->meta = meta;
 	zram->comp = comp;
 	zram->disksize = disksize;
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+	setup_init_done(zram, true);
 	up_write(&zram->init_lock);
 
 	/*

@@ -797,10 +828,8 @@ static ssize_t disksize_store(struct device *dev,
 
 	return len;
 
-out_destroy_comp:
-	up_write(&zram->init_lock);
-	zcomp_destroy(comp);
 out_free_meta:
+	up_write(&zram->init_lock);
 	zram_meta_free(meta);
 	return err;
 }

@@ -905,9 +934,10 @@ out:
  */
 static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
+	int idx;
 	struct zram *zram = queue->queuedata;
 
-	down_read(&zram->init_lock);
+	idx = srcu_read_lock(&zram->srcu);
 	if (unlikely(!init_done(zram)))
 		goto error;
 

@@ -918,12 +948,12 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 	}
 
 	__zram_make_request(zram, bio);
-	up_read(&zram->init_lock);
+	srcu_read_unlock(&zram->srcu, idx);
 
 	return;
 
 error:
-	up_read(&zram->init_lock);
+	srcu_read_unlock(&zram->srcu, idx);
 	bio_io_error(bio);
 }
 

@@ -945,18 +975,20 @@ static void zram_slot_free_notify(struct block_device *bdev,
 static int zram_rw_page(struct block_device *bdev, sector_t sector,
 		       struct page *page, int rw)
 {
-	int offset, err;
+	int offset, err, idx;
 	u32 index;
 	struct zram *zram;
 	struct bio_vec bv;
 
 	zram = bdev->bd_disk->private_data;
+	idx = srcu_read_lock(&zram->srcu);
+
 	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
 		atomic64_inc(&zram->stats.invalid_io);
+		srcu_read_unlock(&zram->srcu, idx);
 		return -EINVAL;
 	}
 
-	down_read(&zram->init_lock);
 	if (unlikely(!init_done(zram))) {
 		err = -EIO;
 		goto out_unlock;

@@ -971,7 +1003,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 
 	err = zram_bvec_rw(zram, &bv, index, offset, rw);
 out_unlock:
-	up_read(&zram->init_lock);
+	srcu_read_unlock(&zram->srcu, idx);
 	/*
 	 * If I/O fails, just return error(ie, non-zero) without
 	 * calling page_endio.

@@ -1041,6 +1073,11 @@ static int create_device(struct zram *zram, int device_id)
 
 	init_rwsem(&zram->init_lock);
 
+	if (init_srcu_struct(&zram->srcu)) {
+		pr_err("Error initialize srcu for device %d\n", device_id);
+		goto out;
+	}
+
 	zram->queue = blk_alloc_queue(GFP_KERNEL);
 	if (!zram->queue) {
 		pr_err("Error allocating disk queue for device %d\n",

@@ -1125,8 +1162,8 @@ static void destroy_device(struct zram *zram)
 
 	del_gendisk(zram->disk);
 	put_disk(zram->disk);
-
 	blk_cleanup_queue(zram->queue);
+	cleanup_srcu_struct(&zram->srcu);
 }
 
 static int __init zram_init(void)

index e492f6bf11f1..2042c310aea8 100644
@@ -105,8 +105,13 @@ struct zram {
 	struct gendisk *disk;
 	struct zcomp *comp;
 
+	struct srcu_struct srcu;
+	struct rcu_head rcu;
+
 	/* Prevent concurrent execution of device init, reset and R/W request */
 	struct rw_semaphore init_lock;
+	bool init_done;
+
 	/*
 	 * This is the limit on amount of *uncompressed* worth of data
 	 * we can store in a disk.

1.9.1

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a typo, I meant `->disksize != 0'.

	-ss

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It could be.

What makes you not sure?
I think it's clear and common pattern for smp_[wmb|rmb]. :)

Kind regards,
Minchan Kim

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care to change it?

well... what that "if (ret)" gives? it's almost always true, because the device is initialized during read/write operations (in 99.99% of cases).

-ss

Will try!

If it was your concern, I'm happy to remove the check.(ie, actually, I realized that after I push the button to send). Thanks!

Kind regards,
Minchan Kim

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Thanks a lot, Minchan.

and, guys, sorry for previous html email (I'm sure I toggled the "plain text" mode in gmail web-interface, but somehow it has different meaning in gmail world).

I'm still concerned about performance numbers that I see on my x86_64. it's not always, but mostly slower. I'll give it another try (disable lockdep, etc.), but if we lose 10% on average then, sorry, I'm not so positive about srcu change and will tend to vote for your initial commit that simply moved meta free() out of init_lock and left locking as is (lockdep warning would have been helpful there, because otherwise it just looked like we change code w/o any reason).

what do you thunk?

	-ss

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Surely I agreee with you. If it suffers from 10% performance regression, it's absolutely no go.

However, I believe it should be no loss because that's one of the reason from RCU birth which should be really win in read-side lock path compared to other locking.

Please test it with dd or something for block-based test for removing noise from FS. I also will test it to confirm that with real machine.

Thanks for the review!

Kind regards,
Minchan Kim

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do you test with a single dd thread/process? just dd if=foo of=bar -c... or you start N `dd &' processes?

for a single writer there should be no difference, no doubt. I'm more interested in multi-writer/multi-reader/mixed use cases.

the options that I use are: iozone -t 3 -R -r 16K -s 60M -I +Z and -I is:
-I Use VxFS VX_DIRECT, O_DIRECT,or O_DIRECTIO for all file operations

with O_DIRECT I don't think there is a lot of noise, but I'll try to use different benchmarks a bit later.

	-ss

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I tested it with multiple dd processes.

As you told, the data was not stable.
Anyway, when I read down_read implementation, it's one atomic instruction. Hmm, it seems te be better for srcu_read_lock which does more things. But I guessed most of overhead are from [de]compression, memcpy, clear_page That's why I guessed we don't have measurable difference from that. What's the data pattern if you use iozone? I guess it's really simple pattern compressor can do fast. I used /dev/sda for dd write so more realistic data. Anyway, if we has 10% regression even if the data is simple, I never want to merge it.
I will test it carefully and if it turns out lots regression, surely, I will not go with this and send the original patch again.

Thanks.

Kind regards,
Minchan Kim

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yes. fread test was always slower, and the rest was mostly slower.

srcu looks havier, agree.

by "data pattern" you mean usage scenario? well, I usually use zram for `make -jX', where X=[4..N]. so N concurrent read-write ops scenario.

	-ss

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Hello, Sergey

ffffffff8172c350 <down_read>:

ffffffff8172c350:       e8 7b 3f 00 00          callq  ffffffff817302d0 <__fentry__>
ffffffff8172c355:       55                      push   %rbp
ffffffff8172c356:       48 89 e5                mov    %rsp,%rbp
ffffffff8172c359:       53                      push   %rbx
ffffffff8172c35a:       48 89 fb                mov    %rdi,%rbx
ffffffff8172c35d:       48 83 ec 08             sub    $0x8,%rsp
ffffffff8172c361:       e8 9a e0 ff ff          callq  ffffffff8172a400 <_cond_resched>
ffffffff8172c366:       48 89 d8                mov    %rbx,%rax
ffffffff8172c369:       f0 48 ff 00             lock incq (%rax)
ffffffff8172c36d:       79 05                   jns    ffffffff8172c374 <down_read+0x24>
ffffffff8172c36f:       e8 5c e7 c4 ff          callq  ffffffff8137aad0 <call_rwsem_down_read_failed>
ffffffff8172c374:       48 83 c4 08             add    $0x8,%rsp
ffffffff8172c378:       5b                      pop    %rbx
ffffffff8172c379:       5d                      pop    %rbp
ffffffff8172c37a:       c3                      retq   

ffffffff810eeec0 <__srcu_read_lock>:

ffffffff810eeec0:       e8 0b 14 64 00          callq  ffffffff817302d0 <__fentry__>
ffffffff810eeec5:       48 8b 07                mov    (%rdi),%rax
ffffffff810eeec8:       55                      push   %rbp
ffffffff810eeec9:       48 89 e5                mov    %rsp,%rbp
ffffffff810eeecc:       83 e0 01                and    $0x1,%eax
ffffffff810eeecf:       48 63 d0                movslq %eax,%rdx
ffffffff810eeed2:       48 8b 4f 08             mov    0x8(%rdi),%rcx
ffffffff810eeed6:       65 48 ff 04 d1          incq   %gs:(%rcx,%rdx,8)
ffffffff810eeedb:       0f ae f0                mfence 
ffffffff810eeede:       48 83 c2 02             add    $0x2,%rdx
ffffffff810eeee2:       48 8b 4f 08             mov    0x8(%rdi),%rcx
ffffffff810eeee6:       65 48 ff 04 d1          incq   %gs:(%rcx,%rdx,8)
ffffffff810eeeeb:       5d                      pop    %rbp
ffffffff810eeeec:       c3                      retq   

Yes, __srcu_read_lock is a little bit heavier but the number of instruction are not too much difference to make difference 10%. A culprit is __cond_resched but I don't think, either because our test was CPU intensive soS I don't think schedule latency affects total bandwidth.

More cuprit is your data pattern.
It seems you didn't use scramble_buffers=0, zero_buffers in fio so that fio fills random data pattern so zram bandwidth could be different by compression/decompression ratio.

I did test your fio script adding above options with my 4 CPU real machine (NOTE, ubuntu fio is old so that it doesn't work well above two options so I should update fio recently which solves it perfectly)

Another thing about fio is it seems loops option works with write test with overwrite=1 options while read test doesn't work so that I should use perf stat -r options to verify stdev.

In addition, I passed first test to remove noise as creating files and increased testsize as 1G from 400m

1) randread

= vanilla =

Performance counter stats for 'fio test-fio-randread.txt' (10 runs):

       4713.879241      task-clock (msec)         #    3.160 CPUs utilized            ( +-  0.62% )
             1,131      context-switches          #    0.240 K/sec                    ( +-  2.83% )
                23      cpu-migrations            #    0.005 K/sec                    ( +-  4.40% )
            15,767      page-faults               #    0.003 M/sec                    ( +-  0.03% )
    15,134,497,088      cycles                    #    3.211 GHz                      ( +-  0.15% ) [83.36%]
    10,763,665,604      stalled-cycles-frontend   #   71.12% frontend cycles idle     ( +-  0.22% ) [83.34%]
     6,896,294,076      stalled-cycles-backend    #   45.57% backend  cycles idle     ( +-  0.29% ) [66.67%]
     9,898,608,791      instructions              #    0.65  insns per cycle        
                                                  #    1.09  stalled cycles per insn  ( +-  0.07% ) [83.33%]
     1,852,167,485      branches                  #  392.918 M/sec                    ( +-  0.07% ) [83.34%]
        14,864,143      branch-misses             #    0.80% of all branches          ( +-  0.16% ) [83.34%]

1.491813361 seconds time elapsed ( +- 0.62% )

= srcu =

Performance counter stats for 'fio test-fio-randread.txt' (10 runs):

       4752.790715      task-clock (msec)         #    3.166 CPUs utilized            ( +-  0.48% )
             1,179      context-switches          #    0.248 K/sec                    ( +-  1.56% )
                26      cpu-migrations            #    0.005 K/sec                    ( +-  3.91% )
            15,764      page-faults               #    0.003 M/sec                    ( +-  0.02% )
    15,263,869,915      cycles                    #    3.212 GHz                      ( +-  0.25% ) [83.32%]
    10,935,658,177      stalled-cycles-frontend   #   71.64% frontend cycles idle     ( +-  0.38% ) [83.33%]
     7,067,290,320      stalled-cycles-backend    #   46.30% backend  cycles idle     ( +-  0.46% ) [66.64%]
     9,896,513,423      instructions              #    0.65  insns per cycle        
                                                  #    1.11  stalled cycles per insn  ( +-  0.07% ) [83.33%]
     1,847,612,285      branches                  #  388.743 M/sec                    ( +-  0.07% ) [83.38%]
        14,814,815      branch-misses             #    0.80% of all branches          ( +-  0.24% ) [83.37%]

1.501284082 seconds time elapsed ( +- 0.50% )

srcu is worse as 0.63% but the difference is really marginal.

2) randwrite

= vanilla =

Performance counter stats for 'fio test-fio-randwrite.txt' (10 runs):

       6283.823490      task-clock (msec)         #    3.332 CPUs utilized            ( +-  0.44% )
             1,536      context-switches          #    0.245 K/sec                    ( +-  2.10% )
                25      cpu-migrations            #    0.004 K/sec                    ( +-  3.79% )
            15,914      page-faults               #    0.003 M/sec                    ( +-  0.02% )
    20,408,942,915      cycles                    #    3.248 GHz                      ( +-  0.40% ) [83.34%]
    14,398,424,739      stalled-cycles-frontend   #   70.55% frontend cycles idle     ( +-  0.62% ) [83.36%]
     9,513,822,555      stalled-cycles-backend    #   46.62% backend  cycles idle     ( +-  0.62% ) [66.65%]
    13,507,376,783      instructions              #    0.66  insns per cycle        
                                                  #    1.07  stalled cycles per insn  ( +-  0.05% ) [83.36%]
     3,155,423,934      branches                  #  502.150 M/sec                    ( +-  0.05% ) [83.34%]
        18,381,090      branch-misses             #    0.58% of all branches          ( +-  0.16% ) [83.34%]

1.885926070 seconds time elapsed ( +- 0.61% )

= srcu =

Performance counter stats for 'fio test-fio-randwrite.txt' (10 runs):

       6152.997119      task-clock (msec)         #    3.304 CPUs utilized            ( +-  0.29% )
             1,422      context-switches          #    0.231 K/sec                    ( +-  3.45% )
                28      cpu-migrations            #    0.004 K/sec                    ( +-  7.47% )
            15,921      page-faults               #    0.003 M/sec                    ( +-  0.02% )
    19,862,315,430      cycles                    #    3.228 GHz                      ( +-  0.09% ) [83.33%]
    13,872,541,761      stalled-cycles-frontend   #   69.84% frontend cycles idle     ( +-  0.12% ) [83.34%]
     9,074,883,552      stalled-cycles-backend    #   45.69% backend  cycles idle     ( +-  0.19% ) [66.71%]
    13,494,854,651      instructions              #    0.68  insns per cycle        
                                                  #    1.03  stalled cycles per insn  ( +-  0.03% ) [83.37%]
     3,148,938,955      branches                  #  511.773 M/sec                    ( +-  0.04% ) [83.33%]
        17,701,249      branch-misses             #    0.56% of all branches          ( +-  0.23% ) [83.34%]

1.862543230 seconds time elapsed ( +- 0.35% )

srcu is better as 1.24% is better.

3) randrw

= vanilla =

Performance counter stats for 'fio test-fio-randrw.txt' (10 runs):

       5609.976477      task-clock (msec)         #    3.249 CPUs utilized            ( +-  0.34% )
             1,407      context-switches          #    0.251 K/sec                    ( +-  0.96% )
                25      cpu-migrations            #    0.004 K/sec                    ( +-  5.37% )
            15,906      page-faults               #    0.003 M/sec                    ( +-  0.05% )
    18,090,560,346      cycles                    #    3.225 GHz                      ( +-  0.35% ) [83.36%]
    12,885,393,954      stalled-cycles-frontend   #   71.23% frontend cycles idle     ( +-  0.53% ) [83.33%]
     8,570,185,547      stalled-cycles-backend    #   47.37% backend  cycles idle     ( +-  0.59% ) [66.67%]
    11,771,620,352      instructions              #    0.65  insns per cycle        
                                                  #    1.09  stalled cycles per insn  ( +-  0.05% ) [83.35%]
     2,508,014,871      branches                  #  447.063 M/sec                    ( +-  0.05% ) [83.34%]
        18,585,638      branch-misses             #    0.74% of all branches          ( +-  0.23% ) [83.35%]

1.726691239 seconds time elapsed ( +- 0.40% )

= srcu =

       5475.312828      task-clock (msec)         #    3.246 CPUs utilized            ( +-  0.59% )
             1,399      context-switches          #    0.255 K/sec                    ( +-  1.46% )
                24      cpu-migrations            #    0.004 K/sec                    ( +-  6.27% )
            15,916      page-faults               #    0.003 M/sec                    ( +-  0.04% )
    17,583,197,041      cycles                    #    3.211 GHz                      ( +-  0.11% ) [83.33%]
    12,352,657,985      stalled-cycles-frontend   #   70.25% frontend cycles idle     ( +-  0.16% ) [83.33%]
     8,173,164,212      stalled-cycles-backend    #   46.48% backend  cycles idle     ( +-  0.19% ) [66.70%]
    11,780,176,340      instructions              #    0.67  insns per cycle        
                                                  #    1.05  stalled cycles per insn  ( +-  0.05% ) [83.36%]
     2,506,722,383      branches                  #  457.823 M/sec                    ( +-  0.06% ) [83.35%]
        18,436,877      branch-misses             #    0.74% of all branches          ( +-  0.18% ) [83.32%]

1.686877512 seconds time elapsed ( +- 0.43% )

srcu is better as 2.3%

Srcu is better than down_read but I don't believe either because when I did perf record, [up|down]_read and srcu_read_[lock|unlock] is really minor (about 0.5%) so that I think it's really marginal. (for example, if we removes srcu_read_[un]lock totally, we just enhance about 1%) So, I don't think it's worth.

Okay, if you concerns on the data still, how about this? Even, it would be smaller instructions than [up|down]_read so I guess it could remove your performance concern. But I don't believe it could make significant difference, either.
Hope it addresses your concern.

Thanks.

Hello Minchan,
excellent analysis!

Completely agree.
Shame on me. gotten so used to iozone (iozone uses same data pattern 0xA5, this is +Z option what for), so I didn't even think about data pattern in fio. sorry.

hm, interesting. I'll re-check.

I'm not so upset to lose 0.6234187%. my concerns were about iozone's 10% different (which looks a bit worse).

I'll review your patch. Thanks for your effort.

I see. I never test it with `make' anyway, only iozone +Z.

	-ss

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Hello Minchan,

the idea looks good and this is something I was trying to do, except that I used kref.

some review nitpicks are below. I also posted modified version of your patch so that will save some time.

 drivers/block/zram/zram_drv.c | 82 ++++++++++++++++++++++++++++++-------------
 drivers/block/zram/zram_drv.h | 17 ++++-----
 2 files changed, 66 insertions(+), 33 deletions(-)

index aa5a4c5..6916790 100644
@@ -44,7 +44,7 @@ static const char *default_compressor = "lzo";
 static unsigned int num_devices = 1;
 
 #define ZRAM_ATTR_RO(name)						\
-static ssize_t name##_show(struct device *d,		\
+static ssize_t name##_show(struct device *d,				\
 				struct device_attribute *attr, char *b)	\
 {									\
 	struct zram *zram = dev_to_zram(d);				\

@@ -55,7 +55,7 @@ static DEVICE_ATTR_RO(name);
 
 static inline int init_done(struct zram *zram)
 {
-	return zram->meta != NULL;
+	return atomic_read(&zram->refcount);
 }
 
 static inline struct zram *dev_to_zram(struct device *dev)

@@ -358,6 +358,23 @@ out_error:
 	return NULL;
 }
 
+static inline bool zram_get(struct zram *zram)
+{
+	if (atomic_inc_not_zero(&zram->refcount))
+		return true;
+	return false;
+}
+
+/*
+ * We want to free zram_meta in process context to avoid
+ * deadlock between reclaim path and any other locks
+ */
+static inline void zram_put(struct zram *zram)
+{
+	if (atomic_dec_and_test(&zram->refcount))
+		complete(&zram->io_done);
+}
+
 static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
 {
 	if (*offset + bvec->bv_len >= PAGE_SIZE)

@@ -719,6 +736,9 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 
 static void zram_reset_device(struct zram *zram, bool reset_capacity)
 {
+	struct zram_meta *meta;
+	struct zcomp *comp;
+
 	down_write(&zram->init_lock);
 
 	zram->limit_pages = 0;

@@ -728,14 +748,21 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 		return;
 	}
 
-	zcomp_destroy(zram->comp);
-	zram->max_comp_streams = 1;
-	zram_meta_free(zram->meta, zram->disksize);
-	zram->meta = NULL;
+	meta = zram->meta;
+	comp = zram->comp;
+	/* ->refcount will go down to 0 eventually */
+	zram_put(zram);
+
+	wait_for_completion(&zram->io_done);
+	/* I/O operation under all of CPU are done so let's free */
+	zram_meta_free(meta, disksize);
+	zcomp_destroy(comp);
+
 	/* Reset stats */
 	memset(&zram->stats, 0, sizeof(zram->stats));
-
 	zram->disksize = 0;
+	zram->max_comp_streams = 1;
+
 	if (reset_capacity)
 		set_capacity(zram->disk, 0);
 

@@ -783,6 +810,8 @@ static ssize_t disksize_store(struct device *dev,
 		goto out_destroy_comp;
 	}
 
+	init_completion(&zram->io_done);
+	atomic_set(&zram->refcount, 1);
 	zram->meta = meta;
 	zram->comp = comp;
 	zram->disksize = disksize;

@@ -795,7 +824,6 @@ static ssize_t disksize_store(struct device *dev,
 	 * so that revalidate_disk always sees up-to-date capacity.
 	 */
 	revalidate_disk(zram->disk);
-
 	return len;
 
 out_destroy_comp:

@@ -908,23 +936,24 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
-	down_read(&zram->init_lock);
-	if (unlikely(!init_done(zram)))
+	if (unlikely(!zram_get(zram)))
 		goto error;
 
+	if (unlikely(!init_done(zram)))
+		goto put_zram;
+
 	if (!valid_io_request(zram, bio->bi_iter.bi_sector,
 					bio->bi_iter.bi_size)) {
 		atomic64_inc(&zram->stats.invalid_io);
-		goto error;
+		goto put_zram;
 	}
 
 	__zram_make_request(zram, bio);
-	up_read(&zram->init_lock);
-
+	zram_put(zram);
 	return;
-
+put_zram:
+	zram_put(zram);
 error:
-	up_read(&zram->init_lock);
 	bio_io_error(bio);
 }
 

@@ -946,21 +975,22 @@ static void zram_slot_free_notify(struct block_device *bdev,
 static int zram_rw_page(struct block_device *bdev, sector_t sector,
 		       struct page *page, int rw)
 {
-	int offset, err;
+	int offset, err = -EIO;
 	u32 index;
 	struct zram *zram;
 	struct bio_vec bv;
 
 	zram = bdev->bd_disk->private_data;
+	if (unlikely(!zram_get(zram)))
+		goto out;
+
+	if (unlikely(!init_done(zram)))
+		goto put_zram;
+
 	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
 		atomic64_inc(&zram->stats.invalid_io);
-		return -EINVAL;
-	}
-
-	down_read(&zram->init_lock);
-	if (unlikely(!init_done(zram))) {
-		err = -EIO;
-		goto out_unlock;
+		err = -EINVAL;
+		goto put_zram;
 	}
 
 	index = sector >> SECTORS_PER_PAGE_SHIFT;

@@ -971,8 +1001,9 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 	bv.bv_offset = 0;
 
 	err = zram_bvec_rw(zram, &bv, index, offset, rw);
-out_unlock:
-	up_read(&zram->init_lock);
+put_zram:
+	zram_put(zram);
+out:
 	/*
 	 * If I/O fails, just return error(ie, non-zero) without
 	 * calling page_endio.

@@ -1041,6 +1072,7 @@ static int create_device(struct zram *zram, int device_id)
 	int ret = -ENOMEM;
 
 	init_rwsem(&zram->init_lock);
+	atomic_set(&zram->refcount, 0);
 
 	zram->queue = blk_alloc_queue(GFP_KERNEL);
 	if (!zram->queue) {

index b05a816..7138c82 100644
@@ -100,24 +100,25 @@ struct zram_meta {
 
 struct zram {
 	struct zram_meta *meta;
+	struct zcomp *comp;
 	struct request_queue *queue;
 	struct gendisk *disk;
-	struct zcomp *comp;
-
 	/* Prevent concurrent execution of device init, reset and R/W request */
 	struct rw_semaphore init_lock;
 	/*
-	 * This is the limit on amount of *uncompressed* worth of data
-	 * we can store in a disk.
+	 * the number of pages zram can consume for storing compressed data
 	 */
-	u64 disksize;	/* bytes */
+	unsigned long limit_pages;
+	atomic_t refcount;
 	int max_comp_streams;
+
 	struct zram_stats stats;
+	struct completion io_done; /* notify IO under all of cpu are done */
 	/*
-	 * the number of pages zram can consume for storing compressed data
+	 * This is the limit on amount of *uncompressed* worth of data
+	 * we can store in a disk.
 	 */
-	unsigned long limit_pages;
-
+	u64 disksize;	/* bytes */
 	char compressor[10];
 };
 #endif

Sorry, guys! my bad. the patch I sent to you is incomplete. pelase review this one.

 drivers/block/zram/zram_drv.c | 84 +++++++++++++++++++++++++++++--------------
 drivers/block/zram/zram_drv.h | 17 ++++-----
 2 files changed, 67 insertions(+), 34 deletions(-)

index aa5a4c5..c0b612d 100644
@@ -44,7 +44,7 @@ static const char *default_compressor = "lzo";
 static unsigned int num_devices = 1;
 
 #define ZRAM_ATTR_RO(name)						\
-static ssize_t name##_show(struct device *d,		\
+static ssize_t name##_show(struct device *d,				\
 				struct device_attribute *attr, char *b)	\
 {									\
 	struct zram *zram = dev_to_zram(d);				\

@@ -55,7 +55,7 @@ static DEVICE_ATTR_RO(name);
 
 static inline int init_done(struct zram *zram)
 {
-	return zram->meta != NULL;
+	return atomic_read(&zram->refcount);
 }
 
 static inline struct zram *dev_to_zram(struct device *dev)

@@ -358,6 +358,23 @@ out_error:
 	return NULL;
 }
 
+static inline bool zram_get(struct zram *zram)
+{
+	if (atomic_inc_not_zero(&zram->refcount))
+		return true;
+	return false;
+}
+
+/*
+ * We want to free zram_meta in process context to avoid
+ * deadlock between reclaim path and any other locks
+ */
+static inline void zram_put(struct zram *zram)
+{
+	if (atomic_dec_and_test(&zram->refcount))
+		complete(&zram->io_done);
+}
+
 static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
 {
 	if (*offset + bvec->bv_len >= PAGE_SIZE)

@@ -719,6 +736,10 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 
 static void zram_reset_device(struct zram *zram, bool reset_capacity)
 {
+	struct zram_meta *meta;
+	struct zcomp *comp;
+	u64 disksize;
+
 	down_write(&zram->init_lock);
 
 	zram->limit_pages = 0;

@@ -728,19 +749,25 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 		return;
 	}
 
-	zcomp_destroy(zram->comp);
-	zram->max_comp_streams = 1;
-	zram_meta_free(zram->meta, zram->disksize);
-	zram->meta = NULL;
+	meta = zram->meta;
+	comp = zram->comp;
+	disksize = zram->disksize;
+	/* ->refcount will go down to 0 eventually */
+	zram_put(zram);
+	wait_for_completion(&zram->io_done);
+
 	/* Reset stats */
 	memset(&zram->stats, 0, sizeof(zram->stats));
-
 	zram->disksize = 0;
+	zram->max_comp_streams = 1;
+
 	if (reset_capacity)
 		set_capacity(zram->disk, 0);
 
 	up_write(&zram->init_lock);
-
+	/* I/O operation under all of CPU are done so let's free */
+	zram_meta_free(meta, disksize);
+	zcomp_destroy(comp);
 	/*
 	 * Revalidate disk out of the init_lock to avoid lockdep splat.
 	 * It's okay because disk's capacity is protected by init_lock

@@ -783,6 +810,8 @@ static ssize_t disksize_store(struct device *dev,
 		goto out_destroy_comp;
 	}
 
+	init_completion(&zram->io_done);
+	atomic_set(&zram->refcount, 1);
 	zram->meta = meta;
 	zram->comp = comp;
 	zram->disksize = disksize;

@@ -795,7 +824,6 @@ static ssize_t disksize_store(struct device *dev,
 	 * so that revalidate_disk always sees up-to-date capacity.
 	 */
 	revalidate_disk(zram->disk);
-
 	return len;
 
 out_destroy_comp:

@@ -908,23 +936,24 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
-	down_read(&zram->init_lock);
-	if (unlikely(!init_done(zram)))
+	if (unlikely(!zram_get(zram)))
 		goto error;
 
+	if (unlikely(!init_done(zram)))
+		goto put_zram;
+
 	if (!valid_io_request(zram, bio->bi_iter.bi_sector,
 					bio->bi_iter.bi_size)) {
 		atomic64_inc(&zram->stats.invalid_io);
-		goto error;
+		goto put_zram;
 	}
 
 	__zram_make_request(zram, bio);
-	up_read(&zram->init_lock);
-
+	zram_put(zram);
 	return;
-
+put_zram:
+	zram_put(zram);
 error:
-	up_read(&zram->init_lock);
 	bio_io_error(bio);
 }
 

@@ -946,21 +975,22 @@ static void zram_slot_free_notify(struct block_device *bdev,
 static int zram_rw_page(struct block_device *bdev, sector_t sector,
 		       struct page *page, int rw)
 {
-	int offset, err;
+	int offset, err = -EIO;
 	u32 index;
 	struct zram *zram;
 	struct bio_vec bv;
 
 	zram = bdev->bd_disk->private_data;
+	if (unlikely(!zram_get(zram)))
+		goto out;
+
+	if (unlikely(!init_done(zram)))
+		goto put_zram;
+
 	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
 		atomic64_inc(&zram->stats.invalid_io);
-		return -EINVAL;
-	}
-
-	down_read(&zram->init_lock);
-	if (unlikely(!init_done(zram))) {
-		err = -EIO;
-		goto out_unlock;
+		err = -EINVAL;
+		goto put_zram;
 	}
 
 	index = sector >> SECTORS_PER_PAGE_SHIFT;

@@ -971,8 +1001,9 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 	bv.bv_offset = 0;
 
 	err = zram_bvec_rw(zram, &bv, index, offset, rw);
-out_unlock:
-	up_read(&zram->init_lock);
+put_zram:
+	zram_put(zram);
+out:
 	/*
 	 * If I/O fails, just return error(ie, non-zero) without
 	 * calling page_endio.

@@ -1041,6 +1072,7 @@ static int create_device(struct zram *zram, int device_id)
 	int ret = -ENOMEM;
 
 	init_rwsem(&zram->init_lock);
+	atomic_set(&zram->refcount, 0);
 
 	zram->queue = blk_alloc_queue(GFP_KERNEL);
 	if (!zram->queue) {

index b05a816..7138c82 100644
@@ -100,24 +100,25 @@ struct zram_meta {
 
 struct zram {
 	struct zram_meta *meta;
+	struct zcomp *comp;
 	struct request_queue *queue;
 	struct gendisk *disk;
-	struct zcomp *comp;
-
 	/* Prevent concurrent execution of device init, reset and R/W request */
 	struct rw_semaphore init_lock;
 	/*
-	 * This is the limit on amount of *uncompressed* worth of data
-	 * we can store in a disk.
+	 * the number of pages zram can consume for storing compressed data
 	 */
-	u64 disksize;	/* bytes */
+	unsigned long limit_pages;
+	atomic_t refcount;
 	int max_comp_streams;
+
 	struct zram_stats stats;
+	struct completion io_done; /* notify IO under all of cpu are done */
 	/*
-	 * the number of pages zram can consume for storing compressed data
+	 * This is the limit on amount of *uncompressed* worth of data
+	 * we can store in a disk.
 	 */
-	unsigned long limit_pages;
-
+	u64 disksize;	/* bytes */
 	char compressor[10];
 };
 #endif

just as I said in my previous email -- is this live lock really possible? we need to umount device to continue with reset. and umount will kill IOs out of our way.

the other reset caller is __exit zram_exit(). but once again, I don't expect this function being executed on mounted device and module being in use.

yes, I think it can do the trick.

	-ss

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Hey, it's not a trick. It suits for the our goal well. Completion was too much, I think.

Kind regards,
Minchan Kim

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sure :)

	-ss

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Hey Sergey,

Thanks a lot!

There was a reason I didn't use refcount there.
I should have written down it.

We need something to prevent further I/O handling on other CPUs. Otherwise, it's livelock. For example, new 'A' I/O rw path on CPU 1 can see non-zero refcount if another CPU is going on rw. Then, another new 'B' I/O rw path on CPU 2 can see non-zero refcount if A I/O is going on. Then, another new 'C' I/O rw path on CPU 3 can see non-zero refcount if B I/O is going on. Finally, 'A' IO is done on CPU 1 and next I/O 'D' on CPU 1 can see non-zero refcount because 'C' on CPU 3 is going on. Infinite loop.

Thanks!

True.

Yeb.

True.
Actually, it was totally RFC I forgot adding the tag in the night but I can't escape from my shame with the escuse. Thanks!

Good idea but still want to name it as zram_meta_get/put because zram_get naming might confuse struct zram's refcount rather than zram_meta. :)

Kind regards,
Minchan Kim

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Hello Minchan,

sure, I did think about this. and I actually didn't find any reason not to use ->refcount there. if user wants to reset the device, he first should umount it to make bdev->bd_holders check happy. and that's where IOs will be failed. so it makes sense to switch to ->refcount there, IMHO.

no problem at all. you were throwing solutions all week long.

no objections. but I assume we agreed to keep ->io_done completion and ->refcount in zram.

	-ss

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If we use zram as block device itself(not a fs or swap) and open the block device as !FMODE_EXCL, bd_holders will be void.

Another topic: As I didn't see enough fs/block_dev.c bd_holders in zram would be mess. I guess we need to study hotplug of device and implement it for zram reset rather than strange own konb. It should go TODO. :(

Kind regards,
Minchan Kim

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hm.
I don't mind to use ->disksize there, but personally I'd maybe prefer to use ->refcount, which just looks less hacky. zram's most common use cases are coming from ram swap device or ram device with fs. so it looks a bit like we care about some corner case here.

just my opinion, no objections against ->disksize != 0.

I need to check fs/block_dev. can we switch away from ->bd_holders?

ok, need to investigate this later.
let's land current activities first.

	-ss

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Maybe, but I always test zram with dd so it's not a corner case for me. :)

Thanks. It's a draft for v2. Please review.

BTW, you pointed out race between bdev_open/close and reset and it's cleary bug although it's rare in real practice.
So, I want to fix it earlier than this patch and mark it as -stable if we can fix it easily like Ganesh's work.
If it gets landing, we could make this patch rebased on it.

the patch mosly looks good, except for one place:

[..]

	atomic_set(&zram->refcount, 0)

	-ss

Everything are fixed. Ready to send a patch. But before sending, hope we fix umount race issue first.

Thanks a lot, Sergey!

Kind regards,
Minchan Kim

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Thanks a lot, Minchan!

OK, surely I don't mind to fix the umount race first, I just didn't want to interrupt you in the middle of locking rework. the race is hardly possible, but still.

I didn't review Ganesh's patch yet, I'll try to find some time to take a look later this day.

I'm also planning to send a small `struct zram' cleanup patch by the end of this day.

	-ss

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Hello,

fio test (http://manpages.ubuntu.com/manpages/natty/man1/fio.1.html) configs are attached, so we can run fio on different h/w (works against zram with fs mounted at /mnt/)

for i in ./test-fio-*; do fio ./$i; rm bg*; done

in short

randread
BASE READ: io=1600.0MB, aggrb=3747.8MB/s, minb=959250KB/s, maxb=982.82MB/s, mint=407msec, maxt=427msec
SRCU READ: io=1600.0MB, aggrb=3782.6MB/s, minb=968321KB/s, maxb=977.11MB/s, mint=409msec, maxt=423msec

random read/write
BASE READ: io=820304KB, aggrb=1296.3MB/s, minb=331838KB/s, maxb=333456KB/s, mint=615msec, maxt=618msec
SRCU READ: io=820304KB, aggrb=1261.6MB/s, minb=322954KB/s, maxb=335639KB/s, mint=611msec, maxt=635msec
BASE WRITE: io=818096KB, aggrb=1292.8MB/s, minb=330944KB/s, maxb=332559KB/s, mint=615msec, maxt=618msec SRCU WRITE: io=818096KB, aggrb=1258.2MB/s, minb=322085KB/s, maxb=334736KB/s, mint=611msec, maxt=635msec

random write
BASE WRITE: io=1600.0MB, aggrb=692184KB/s, minb=173046KB/s, maxb=174669KB/s, mint=2345msec, maxt=2367msec SRCU WRITE: io=1600.0MB, aggrb=672577KB/s, minb=168144KB/s, maxb=174149KB/s, mint=2352msec, maxt=2436msec

detailed per-process metrics:

************* BASE *************

$ for i in ./test-fio-*; do fio ./$i; rm bg*; done
bgreader: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)

bgreader: (groupid=0, jobs=1): err= 0: pid=10792: Thu Jan 29 19:43:30 2015
read : io=409600KB, bw=959251KB/s, iops=239812, runt= 427msec

    slat (usec): min=2, max=28, avg= 2.43, stdev= 0.62
    clat (usec): min=1, max=151, avg=122.97, stdev= 4.99
     lat (usec): min=4, max=174, avg=125.52, stdev= 5.08
    clat percentiles (usec):
     |  1.00th=[  106],  5.00th=[  116], 10.00th=[  121], 20.00th=[  122],
     | 30.00th=[  122], 40.00th=[  123], 50.00th=[  123], 60.00th=[  124],
     | 70.00th=[  124], 80.00th=[  124], 90.00th=[  125], 95.00th=[  127],
     | 99.00th=[  143], 99.50th=[  143], 99.90th=[  145], 99.95th=[  145],
     | 99.99th=[  147]
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.97%
  cpu          : usr=39.11%, sys=55.04%, ctx=82, majf=0, minf=38
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=10793: Thu Jan 29 19:43:30 2015
  read : io=409600KB, bw=982254KB/s, iops=245563, runt=   417msec
    slat (usec): min=2, max=60, avg= 2.42, stdev= 0.56
    clat (usec): min=1, max=187, avg=123.17, stdev= 4.02
     lat (usec): min=3, max=189, avg=125.71, stdev= 4.09
    clat percentiles (usec):
     |  1.00th=[  105],  5.00th=[  121], 10.00th=[  121], 20.00th=[  122],
     | 30.00th=[  122], 40.00th=[  123], 50.00th=[  123], 60.00th=[  124],
     | 70.00th=[  124], 80.00th=[  125], 90.00th=[  126], 95.00th=[  127],
     | 99.00th=[  133], 99.50th=[  135], 99.90th=[  141], 99.95th=[  175],
     | 99.99th=[  187]
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.97%
  cpu          : usr=40.53%, sys=55.88%, ctx=43, majf=0, minf=39
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=10794: Thu Jan 29 19:43:30 2015
  read : io=409600KB, bw=982.82MB/s, iops=251597, runt=   407msec
    slat (usec): min=2, max=50, avg= 2.43, stdev= 0.58
    clat (usec): min=2, max=174, avg=123.07, stdev= 3.97
     lat (usec): min=5, max=197, avg=125.62, stdev= 4.02
    clat percentiles (usec):
     |  1.00th=[  106],  5.00th=[  120], 10.00th=[  121], 20.00th=[  122],
     | 30.00th=[  122], 40.00th=[  123], 50.00th=[  123], 60.00th=[  123],
     | 70.00th=[  124], 80.00th=[  125], 90.00th=[  126], 95.00th=[  129],
     | 99.00th=[  135], 99.50th=[  137], 99.90th=[  145], 99.95th=[  153],
     | 99.99th=[  169]
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.98%
  cpu          : usr=41.03%, sys=57.74%, ctx=42, majf=0, minf=37
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=10795: Thu Jan 29 19:43:30 2015
  read : io=409600KB, bw=980.41MB/s, iops=250980, runt=   408msec
    slat (usec): min=2, max=357, avg= 2.45, stdev= 1.32
    clat (usec): min=1, max=498, avg=124.23, stdev=12.09
     lat (usec): min=4, max=501, avg=126.80, stdev=12.33
    clat percentiles (usec):
     |  1.00th=[  108],  5.00th=[  121], 10.00th=[  122], 20.00th=[  122],
     | 30.00th=[  123], 40.00th=[  123], 50.00th=[  124], 60.00th=[  124],
     | 70.00th=[  124], 80.00th=[  125], 90.00th=[  126], 95.00th=[  127],
     | 99.00th=[  139], 99.50th=[  141], 99.90th=[  274], 99.95th=[  350],
     | 99.99th=[  498]
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.61%, 500=0.37%
  cpu          : usr=41.18%, sys=58.09%, ctx=86, majf=0, minf=38
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
READ: io=1600.0MB, aggrb=3747.8MB/s, minb=959250KB/s, maxb=982.82MB/s, mint=407msec, maxt=427msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
bgupdater: (g=0): rw=randrw, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)

bgupdater: (groupid=0, jobs=1): err= 0: pid=10803: Thu Jan 29 19:43:33 2015
read : io=205076KB, bw=332916KB/s, iops=83228, runt= 616msec

    slat (usec): min=2, max=38, avg= 2.53, stdev= 0.71
    clat (usec): min=18, max=912, avg=187.23, stdev=18.71
     lat (usec): min=22, max=915, avg=189.88, stdev=18.74
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  183], 50.00th=[  187], 60.00th=[  191],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  203], 95.00th=[  209],
     | 99.00th=[  223], 99.50th=[  233], 99.90th=[  258], 99.95th=[  290],
     | 99.99th=[  908]
    bw (KB  /s): min=332504, max=332504, per=25.05%, avg=332504.00, stdev= 0.00
  write: io=204524KB, bw=332019KB/s, iops=83004, runt=   616msec
    slat (usec): min=4, max=731, avg= 6.21, stdev= 3.42
    clat (usec): min=1, max=910, avg=187.36, stdev=17.80
     lat (usec): min=8, max=918, avg=193.71, stdev=18.16
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  185], 50.00th=[  187], 60.00th=[  191],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  203], 95.00th=[  209],
     | 99.00th=[  223], 99.50th=[  231], 99.90th=[  258], 99.95th=[  282],
     | 99.99th=[  908]
    bw (KB  /s): min=332544, max=332544, per=25.12%, avg=332544.00, stdev= 0.00
    lat (usec) : 2=0.01%, 20=0.01%, 50=0.01%, 100=0.01%, 250=99.80%
    lat (usec) : 500=0.15%, 1000=0.03%
  cpu          : usr=30.36%, sys=68.99%, ctx=185, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=10804: Thu Jan 29 19:43:33 2015
  read : io=205076KB, bw=331838KB/s, iops=82959, runt=   618msec
    slat (usec): min=2, max=99, avg= 2.54, stdev= 0.88
    clat (usec): min=13, max=4676, avg=187.64, stdev=78.01
     lat (usec): min=16, max=4678, avg=190.29, stdev=78.01
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  221], 99.50th=[  239], 99.90th=[  342], 99.95th=[  462],
     | 99.99th=[ 4704]
    bw (KB  /s): min=330248, max=330248, per=24.88%, avg=330248.00, stdev= 0.00
  write: io=204524KB, bw=330945KB/s, iops=82736, runt=   618msec
    slat (usec): min=4, max=4458, avg= 6.24, stdev=19.77
    clat (usec): min=2, max=4673, avg=187.90, stdev=80.44
     lat (usec): min=6, max=4680, avg=194.28, stdev=82.87
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  219], 99.50th=[  233], 99.90th=[  342], 99.95th=[  462],
     | 99.99th=[ 4640]
    bw (KB  /s): min=330328, max=330328, per=24.95%, avg=330328.00, stdev= 0.00
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.67%, 500=0.28%
    lat (msec) : 10=0.03%
  cpu          : usr=30.10%, sys=68.45%, ctx=67, majf=0, minf=10
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=10805: Thu Jan 29 19:43:33 2015
  read : io=205076KB, bw=332916KB/s, iops=83228, runt=   616msec
    slat (usec): min=2, max=4810, avg= 2.63, stdev=21.50
    clat (usec): min=14, max=5018, avg=187.75, stdev=99.05
     lat (usec): min=16, max=5020, avg=190.49, stdev=101.38
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  185], 60.00th=[  189],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  219], 99.50th=[  229], 99.90th=[  262], 99.95th=[  956],
     | 99.99th=[ 5024]
    bw (KB  /s): min=331056, max=331056, per=24.94%, avg=331056.00, stdev= 0.00
  write: io=204524KB, bw=332019KB/s, iops=83004, runt=   616msec
    slat (usec): min=4, max=49, avg= 6.11, stdev= 1.01
    clat (usec): min=2, max=5018, avg=186.97, stdev=70.14
     lat (usec): min=6, max=5024, avg=193.22, stdev=70.15
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  195], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  217], 99.50th=[  227], 99.90th=[  255], 99.95th=[  948],
     | 99.99th=[ 5024]
    bw (KB  /s): min=331320, max=331320, per=25.03%, avg=331320.00, stdev= 0.00
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.83%, 500=0.09%, 1000=0.03%
    lat (msec) : 10=0.03%
  cpu          : usr=30.52%, sys=68.34%, ctx=70, majf=0, minf=8
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=10806: Thu Jan 29 19:43:33 2015
  read : io=205076KB, bw=333457KB/s, iops=83364, runt=   615msec
    slat (usec): min=2, max=40, avg= 2.53, stdev= 0.69
    clat (usec): min=18, max=287, avg=186.73, stdev=12.94
     lat (usec): min=21, max=289, avg=189.38, stdev=12.98
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  203], 95.00th=[  207],
     | 99.00th=[  221], 99.50th=[  229], 99.90th=[  258], 99.95th=[  270],
     | 99.99th=[  286]
    bw (KB  /s): min=332680, max=332680, per=25.06%, avg=332680.00, stdev= 0.00
  write: io=204524KB, bw=332559KB/s, iops=83139, runt=   615msec
    slat (usec): min=4, max=28, avg= 6.17, stdev= 1.02
    clat (usec): min=2, max=285, avg=186.95, stdev=12.80
     lat (usec): min=8, max=294, avg=193.26, stdev=12.89
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  185], 50.00th=[  187], 60.00th=[  191],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  203], 95.00th=[  209],
     | 99.00th=[  221], 99.50th=[  227], 99.90th=[  251], 99.95th=[  262],
     | 99.99th=[  274]
    bw (KB  /s): min=332672, max=332672, per=25.13%, avg=332672.00, stdev= 0.00
    lat (usec) : 4=0.01%, 20=0.01%, 50=0.01%, 100=0.01%, 250=99.85%
    lat (usec) : 500=0.14%
  cpu          : usr=30.73%, sys=69.11%, ctx=63, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
READ: io=820304KB, aggrb=1296.3MB/s, minb=331838KB/s, maxb=333456KB/s, mint=615msec, maxt=618msec
WRITE: io=818096KB, aggrb=1292.8MB/s, minb=330944KB/s, maxb=332559KB/s, mint=615msec, maxt=618msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
bgwriter: (g=0): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
Jobs: 4 (f=4)
bgwriter: (groupid=0, jobs=1): err= 0: pid=10814: Thu Jan 29 19:43:35 2015
write: io=409600KB, bw=174150KB/s, iops=43537, runt= 2352msec

    slat (usec): min=11, max=3866, avg=20.72, stdev=14.58
    clat (usec): min=2, max=5074, avg=712.72, stdev=92.15
     lat (usec): min=20, max=5094, avg=733.63, stdev=93.77
    clat percentiles (usec):
     |  1.00th=[  612],  5.00th=[  676], 10.00th=[  684], 20.00th=[  700],
     | 30.00th=[  700], 40.00th=[  708], 50.00th=[  708], 60.00th=[  716],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  732], 95.00th=[  740],
     | 99.00th=[  820], 99.50th=[ 1004], 99.90th=[ 1640], 99.95th=[ 2128],
     | 99.99th=[ 5088]
    bw (KB  /s): min=170904, max=174808, per=24.97%, avg=172816.00, stdev=1847.92
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.24%
    lat (usec) : 750=96.28%, 1000=2.94%
    lat (msec) : 2=0.46%, 4=0.03%, 10=0.03%
  cpu          : usr=10.67%, sys=88.52%, ctx=267, majf=0, minf=8
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=10815: Thu Jan 29 19:43:35 2015
  write: io=409600KB, bw=173046KB/s, iops=43261, runt=  2367msec
    slat (usec): min=12, max=1459, avg=20.87, stdev=10.16
    clat (usec): min=2, max=2804, avg=717.25, stdev=69.33
     lat (usec): min=22, max=2825, avg=738.31, stdev=70.84
    clat percentiles (usec):
     |  1.00th=[  628],  5.00th=[  676], 10.00th=[  692], 20.00th=[  700],
     | 30.00th=[  708], 40.00th=[  708], 50.00th=[  716], 60.00th=[  716],
     | 70.00th=[  724], 80.00th=[  732], 90.00th=[  740], 95.00th=[  748],
     | 99.00th=[  812], 99.50th=[ 1080], 99.90th=[ 1800], 99.95th=[ 1992],
     | 99.99th=[ 2640]
    bw (KB  /s): min=171160, max=172768, per=24.82%, avg=171786.00, stdev=761.48
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.11%
    lat (usec) : 750=95.99%, 1000=3.25%
    lat (msec) : 2=0.60%, 4=0.04%
  cpu          : usr=10.65%, sys=88.64%, ctx=502, majf=0, minf=9
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=10816: Thu Jan 29 19:43:35 2015
  write: io=409600KB, bw=174224KB/s, iops=43555, runt=  2351msec
    slat (usec): min=12, max=280, avg=20.67, stdev= 2.58
    clat (usec): min=2, max=1116, avg=712.42, stdev=31.10
     lat (usec): min=20, max=1145, avg=733.30, stdev=31.89
    clat percentiles (usec):
     |  1.00th=[  628],  5.00th=[  676], 10.00th=[  684], 20.00th=[  700],
     | 30.00th=[  708], 40.00th=[  708], 50.00th=[  716], 60.00th=[  716],
     | 70.00th=[  724], 80.00th=[  724], 90.00th=[  740], 95.00th=[  748],
     | 99.00th=[  772], 99.50th=[  788], 99.90th=[ 1020], 99.95th=[ 1048],
     | 99.99th=[ 1080]
    bw (KB  /s): min=171632, max=174888, per=25.00%, avg=173026.00, stdev=1359.10
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.11%
    lat (usec) : 750=94.50%, 1000=5.19%
    lat (msec) : 2=0.19%
  cpu          : usr=10.85%, sys=88.77%, ctx=472, majf=0, minf=8
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=10817: Thu Jan 29 19:43:35 2015
  write: io=409600KB, bw=174670KB/s, iops=43667, runt=  2345msec
    slat (usec): min=11, max=6296, avg=20.66, stdev=24.99
    clat (usec): min=2, max=5509, avg=708.98, stdev=90.54
     lat (usec): min=22, max=7099, avg=729.83, stdev=94.22
    clat percentiles (usec):
     |  1.00th=[  604],  5.00th=[  676], 10.00th=[  684], 20.00th=[  700],
     | 30.00th=[  700], 40.00th=[  708], 50.00th=[  708], 60.00th=[  716],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  732], 95.00th=[  740],
     | 99.00th=[  756], 99.50th=[  772], 99.90th=[  940], 99.95th=[ 1912],
     | 99.99th=[ 5536]
    bw (KB  /s): min=170792, max=176064, per=25.05%, avg=173360.00, stdev=2157.10
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.32%
    lat (usec) : 750=97.68%, 1000=1.92%
    lat (msec) : 2=0.03%, 10=0.03%
  cpu          : usr=10.79%, sys=88.53%, ctx=252, majf=0, minf=6
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
WRITE: io=1600.0MB, aggrb=692184KB/s, minb=173046KB/s, maxb=174669KB/s, mint=2345msec, maxt=2367msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%

==========================================================================================================

************* SRCU *************

$ for i in ./test-fio-*; do fio ./$i; rm bg*; done
bgreader: (g=0): rw=randread, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)
bgreader: Laying out IO file(s) (1 file(s) / 400MB)

bgreader: (groupid=0, jobs=1): err= 0: pid=11578: Thu Jan 29 19:45:01 2015
read : io=409600KB, bw=986988KB/s, iops=246746, runt= 415msec

    slat (usec): min=2, max=708, avg= 2.48, stdev= 2.29
    clat (usec): min=2, max=839, avg=124.69, stdev=16.01
     lat (usec): min=4, max=842, avg=127.29, stdev=16.29
    clat percentiles (usec):
     |  1.00th=[  121],  5.00th=[  122], 10.00th=[  122], 20.00th=[  122],
     | 30.00th=[  123], 40.00th=[  123], 50.00th=[  123], 60.00th=[  123],
     | 70.00th=[  124], 80.00th=[  124], 90.00th=[  125], 95.00th=[  131],
     | 99.00th=[  139], 99.50th=[  223], 99.90th=[  243], 99.95th=[  282],
     | 99.99th=[  836]
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.90%, 500=0.05%, 1000=0.03%
  cpu          : usr=40.48%, sys=57.11%, ctx=46, majf=0, minf=39
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=11579: Thu Jan 29 19:45:01 2015
  read : io=409600KB, bw=968322KB/s, iops=242080, runt=   423msec
    slat (usec): min=2, max=88, avg= 2.45, stdev= 0.67
    clat (usec): min=1, max=213, avg=123.41, stdev= 4.23
     lat (usec): min=3, max=216, avg=125.97, stdev= 4.30
    clat percentiles (usec):
     |  1.00th=[  108],  5.00th=[  121], 10.00th=[  122], 20.00th=[  122],
     | 30.00th=[  123], 40.00th=[  123], 50.00th=[  123], 60.00th=[  124],
     | 70.00th=[  124], 80.00th=[  124], 90.00th=[  125], 95.00th=[  126],
     | 99.00th=[  139], 99.50th=[  139], 99.90th=[  145], 99.95th=[  195],
     | 99.99th=[  213]
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.97%
  cpu          : usr=39.24%, sys=55.79%, ctx=85, majf=0, minf=39
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=11580: Thu Jan 29 19:45:01 2015
  read : io=409600KB, bw=984615KB/s, iops=246153, runt=   416msec
    slat (usec): min=2, max=51, avg= 2.42, stdev= 0.63
    clat (usec): min=2, max=171, avg=123.01, stdev= 3.46
     lat (usec): min=4, max=174, avg=125.55, stdev= 3.50
    clat percentiles (usec):
     |  1.00th=[  120],  5.00th=[  121], 10.00th=[  121], 20.00th=[  122],
     | 30.00th=[  122], 40.00th=[  122], 50.00th=[  122], 60.00th=[  123],
     | 70.00th=[  123], 80.00th=[  123], 90.00th=[  124], 95.00th=[  126],
     | 99.00th=[  141], 99.50th=[  143], 99.90th=[  145], 99.95th=[  155],
     | 99.99th=[  171]
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.97%
  cpu          : usr=40.38%, sys=56.25%, ctx=82, majf=0, minf=37
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgreader: (groupid=0, jobs=1): err= 0: pid=11581: Thu Jan 29 19:45:01 2015
  read : io=409600KB, bw=977.11MB/s, iops=250366, runt=   409msec
    slat (usec): min=2, max=236, avg= 2.46, stdev= 0.98
    clat (usec): min=1, max=370, avg=124.55, stdev=11.16
     lat (usec): min=4, max=372, avg=127.12, stdev=11.37
    clat percentiles (usec):
     |  1.00th=[  107],  5.00th=[  121], 10.00th=[  122], 20.00th=[  122],
     | 30.00th=[  123], 40.00th=[  123], 50.00th=[  124], 60.00th=[  124],
     | 70.00th=[  124], 80.00th=[  125], 90.00th=[  125], 95.00th=[  126],
     | 99.00th=[  175], 99.50th=[  223], 99.90th=[  225], 99.95th=[  278],
     | 99.99th=[  370]
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.92%, 500=0.06%
  cpu          : usr=41.56%, sys=57.95%, ctx=48, majf=0, minf=38
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=102400/w=0/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
READ: io=1600.0MB, aggrb=3782.6MB/s, minb=968321KB/s, maxb=977.11MB/s, mint=409msec, maxt=423msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
bgupdater: (g=0): rw=randrw, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)
bgupdater: Laying out IO file(s) (1 file(s) / 400MB)

bgupdater: (groupid=0, jobs=1): err= 0: pid=11592: Thu Jan 29 19:45:04 2015
read : io=205076KB, bw=334545KB/s, iops=83636, runt= 613msec

    slat (usec): min=2, max=73, avg= 2.56, stdev= 0.73
    clat (usec): min=19, max=310, avg=186.14, stdev=13.49
     lat (usec): min=22, max=312, avg=188.81, stdev=13.55
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  229], 99.50th=[  251], 99.90th=[  266], 99.95th=[  274],
     | 99.99th=[  298]
    bw (KB  /s): min=333496, max=333496, per=25.82%, avg=333496.00, stdev= 0.00
  write: io=204524KB, bw=333644KB/s, iops=83411, runt=   613msec
    slat (usec): min=4, max=30, avg= 6.10, stdev= 1.01
    clat (usec): min=2, max=307, avg=186.32, stdev=13.35
     lat (usec): min=8, max=313, avg=192.56, stdev=13.47
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  177],
     | 30.00th=[  181], 40.00th=[  183], 50.00th=[  187], 60.00th=[  189],
     | 70.00th=[  193], 80.00th=[  197], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  227], 99.50th=[  249], 99.90th=[  266], 99.95th=[  274],
     | 99.99th=[  298]
    bw (KB  /s): min=333368, max=333368, per=25.88%, avg=333368.00, stdev= 0.00
    lat (usec) : 4=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=99.47%, 500=0.51%
  cpu          : usr=30.51%, sys=69.00%, ctx=68, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=11593: Thu Jan 29 19:45:04 2015
  read : io=205076KB, bw=334545KB/s, iops=83636, runt=   613msec
    slat (usec): min=2, max=40, avg= 2.53, stdev= 0.65
    clat (usec): min=53, max=3694, avg=186.31, stdev=65.12
     lat (usec): min=55, max=3697, avg=188.96, stdev=65.13
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  181], 50.00th=[  185], 60.00th=[  187],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  201], 95.00th=[  207],
     | 99.00th=[  231], 99.50th=[  249], 99.90th=[  266], 99.95th=[  342],
     | 99.99th=[ 3696]
    bw (KB  /s): min=335528, max=335528, per=25.97%, avg=335528.00, stdev= 0.00
  write: io=204524KB, bw=333644KB/s, iops=83411, runt=   613msec
    slat (usec): min=4, max=160, avg= 6.08, stdev= 1.22
    clat (usec): min=2, max=3693, avg=186.31, stdev=59.38
     lat (usec): min=44, max=3699, avg=192.54, stdev=59.41
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  185], 60.00th=[  189],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  201], 95.00th=[  205],
     | 99.00th=[  225], 99.50th=[  247], 99.90th=[  262], 99.95th=[  346],
     | 99.99th=[ 3696]
    bw (KB  /s): min=335376, max=335376, per=26.03%, avg=335376.00, stdev= 0.00
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=99.55%, 500=0.41%
    lat (msec) : 4=0.03%
  cpu          : usr=30.34%, sys=68.68%, ctx=64, majf=0, minf=9
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=11594: Thu Jan 29 19:45:04 2015
  read : io=205076KB, bw=322954KB/s, iops=80738, runt=   635msec
    slat (usec): min=2, max=9087, avg= 2.75, stdev=41.31
    clat (usec): min=13, max=9287, avg=193.88, stdev=237.09
     lat (usec): min=15, max=9293, avg=196.75, stdev=240.69
    clat percentiles (usec):
     |  1.00th=[  143],  5.00th=[  163], 10.00th=[  169], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  181], 50.00th=[  185], 60.00th=[  189],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  201], 95.00th=[  209],
     | 99.00th=[  255], 99.50th=[  350], 99.90th=[ 3536], 99.95th=[ 8256],
     | 99.99th=[ 9280]
    bw (KB  /s): min=324248, max=324248, per=25.10%, avg=324248.00, stdev= 0.00
  write: io=204524KB, bw=322085KB/s, iops=80521, runt=   635msec
    slat (usec): min=3, max=3360, avg= 6.20, stdev=15.91
    clat (usec): min=1, max=9286, avg=192.34, stdev=210.71
     lat (usec): min=6, max=9293, avg=198.68, stdev=211.36
    clat percentiles (usec):
     |  1.00th=[  145],  5.00th=[  163], 10.00th=[  169], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  185], 60.00th=[  189],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  203], 95.00th=[  209],
     | 99.00th=[  253], 99.50th=[  346], 99.90th=[ 1032], 99.95th=[ 8256],
     | 99.99th=[ 9280]
    bw (KB  /s): min=324656, max=324656, per=25.20%, avg=324656.00, stdev= 0.00
    lat (usec) : 2=0.01%, 10=0.01%, 20=0.01%, 50=0.01%, 100=0.01%
    lat (usec) : 250=98.84%, 500=0.93%, 750=0.05%
    lat (msec) : 2=0.03%, 4=0.06%, 10=0.06%
  cpu          : usr=29.29%, sys=66.14%, ctx=91, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgupdater: (groupid=0, jobs=1): err= 0: pid=11595: Thu Jan 29 19:45:04 2015
  read : io=205076KB, bw=335640KB/s, iops=83909, runt=   611msec
    slat (usec): min=2, max=58, avg= 2.56, stdev= 0.82
    clat (usec): min=17, max=470, avg=185.51, stdev=15.09
     lat (usec): min=20, max=472, avg=188.18, stdev=15.16
    clat percentiles (usec):
     |  1.00th=[  157],  5.00th=[  167], 10.00th=[  171], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  181], 50.00th=[  185], 60.00th=[  187],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  201], 95.00th=[  209],
     | 99.00th=[  233], 99.50th=[  251], 99.90th=[  270], 99.95th=[  330],
     | 99.99th=[  462]
    bw (KB  /s): min=334544, max=334544, per=25.90%, avg=334544.00, stdev= 0.00
  write: io=204524KB, bw=334736KB/s, iops=83684, runt=   611msec
    slat (usec): min=4, max=90, avg= 6.07, stdev= 1.19
    clat (usec): min=2, max=468, avg=185.70, stdev=14.68
     lat (usec): min=8, max=474, avg=191.91, stdev=14.84
    clat percentiles (usec):
     |  1.00th=[  159],  5.00th=[  167], 10.00th=[  171], 20.00th=[  175],
     | 30.00th=[  179], 40.00th=[  183], 50.00th=[  185], 60.00th=[  189],
     | 70.00th=[  191], 80.00th=[  195], 90.00th=[  203], 95.00th=[  209],
     | 99.00th=[  231], 99.50th=[  249], 99.90th=[  266], 99.95th=[  274],
     | 99.99th=[  462]
    bw (KB  /s): min=334440, max=334440, per=25.96%, avg=334440.00, stdev= 0.00
    lat (usec) : 4=0.01%, 20=0.01%, 50=0.01%, 100=0.01%, 250=99.48%
    lat (usec) : 500=0.51%
  cpu          : usr=30.44%, sys=68.58%, ctx=188, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=51269/w=51131/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
READ: io=820304KB, aggrb=1261.6MB/s, minb=322954KB/s, maxb=335639KB/s, mint=611msec, maxt=635msec
WRITE: io=818096KB, aggrb=1258.2MB/s, minb=322085KB/s, maxb=334736KB/s, mint=611msec, maxt=635msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
bgwriter: (g=0): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=libaio, iodepth=32
...
fio-2.2.5
Starting 4 processes
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
bgwriter: Laying out IO file(s) (1 file(s) / 400MB)
Jobs: 4 (f=4)
bgwriter: (groupid=0, jobs=1): err= 0: pid=11605: Thu Jan 29 19:45:06 2015
write: io=409600KB, bw=168144KB/s, iops=42036, runt= 2436msec

    slat (usec): min=10, max=5615, avg=21.50, stdev=37.53
    clat (usec): min=2, max=9808, avg=738.51, stdev=364.25
     lat (usec): min=40, max=9827, avg=760.22, stdev=371.10
    clat percentiles (usec):
     |  1.00th=[  612],  5.00th=[  668], 10.00th=[  684], 20.00th=[  692],
     | 30.00th=[  700], 40.00th=[  700], 50.00th=[  708], 60.00th=[  708],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  732], 95.00th=[  756],
     | 99.00th=[ 1576], 99.50th=[ 3056], 99.90th=[ 6816], 99.95th=[ 9408],
     | 99.99th=[ 9792]
    bw (KB  /s): min=157408, max=176360, per=24.65%, avg=165770.00, stdev=8401.50
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.20%
    lat (usec) : 750=94.24%, 1000=4.14%
    lat (msec) : 2=0.63%, 4=0.45%, 10=0.33%
  cpu          : usr=10.26%, sys=85.22%, ctx=982, majf=0, minf=7
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=11606: Thu Jan 29 19:45:06 2015
  write: io=409600KB, bw=173928KB/s, iops=43481, runt=  2355msec
    slat (usec): min=12, max=1173, avg=20.76, stdev= 7.22
    clat (usec): min=2, max=2247, avg=713.64, stdev=49.05
     lat (usec): min=22, max=2270, avg=734.58, stdev=50.26
    clat percentiles (usec):
     |  1.00th=[  620],  5.00th=[  668], 10.00th=[  684], 20.00th=[  692],
     | 30.00th=[  700], 40.00th=[  708], 50.00th=[  708], 60.00th=[  716],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  740], 95.00th=[  756],
     | 99.00th=[  868], 99.50th=[  924], 99.90th=[ 1368], 99.95th=[ 1608],
     | 99.99th=[ 2192]
    bw (KB  /s): min=170448, max=175504, per=25.63%, avg=172406.00, stdev=2166.56
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.13%
    lat (usec) : 750=92.77%, 1000=6.92%
    lat (msec) : 2=0.17%, 4=0.01%
  cpu          : usr=10.66%, sys=88.66%, ctx=528, majf=0, minf=8
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=11607: Thu Jan 29 19:45:06 2015
  write: io=409600KB, bw=172900KB/s, iops=43224, runt=  2369msec
    slat (usec): min=9, max=3458, avg=20.88, stdev=19.13
    clat (usec): min=2, max=4190, avg=718.03, stdev=114.69
     lat (usec): min=22, max=4210, avg=739.09, stdev=116.47
    clat percentiles (usec):
     |  1.00th=[  620],  5.00th=[  668], 10.00th=[  684], 20.00th=[  692],
     | 30.00th=[  700], 40.00th=[  700], 50.00th=[  708], 60.00th=[  708],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  732], 95.00th=[  756],
     | 99.00th=[ 1064], 99.50th=[ 1080], 99.90th=[ 2024], 99.95th=[ 3952],
     | 99.99th=[ 4192]
    bw (KB  /s): min=168600, max=173752, per=25.49%, avg=171458.00, stdev=2129.26
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.14%
    lat (usec) : 750=94.29%, 1000=2.69%
    lat (msec) : 2=2.74%, 4=0.09%, 10=0.03%
  cpu          : usr=10.55%, sys=87.38%, ctx=373, majf=0, minf=8
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32
bgwriter: (groupid=0, jobs=1): err= 0: pid=11608: Thu Jan 29 19:45:06 2015
  write: io=409600KB, bw=174150KB/s, iops=43537, runt=  2352msec
    slat (usec): min=9, max=5199, avg=20.79, stdev=26.32
    clat (usec): min=2, max=5915, avg=712.94, stdev=149.06
     lat (usec): min=20, max=5936, avg=733.91, stdev=151.50
    clat percentiles (usec):
     |  1.00th=[  628],  5.00th=[  668], 10.00th=[  684], 20.00th=[  692],
     | 30.00th=[  700], 40.00th=[  708], 50.00th=[  708], 60.00th=[  716],
     | 70.00th=[  716], 80.00th=[  724], 90.00th=[  732], 95.00th=[  740],
     | 99.00th=[  780], 99.50th=[  836], 99.90th=[ 2512], 99.95th=[ 5536],
     | 99.99th=[ 5920]
    bw (KB  /s): min=170872, max=174024, per=25.68%, avg=172714.00, stdev=1386.45
    lat (usec) : 4=0.01%, 50=0.01%, 100=0.01%, 250=0.01%, 500=0.10%
    lat (usec) : 750=97.10%, 1000=2.55%
    lat (msec) : 2=0.08%, 4=0.07%, 10=0.09%
  cpu          : usr=10.50%, sys=88.56%, ctx=260, majf=0, minf=6
  IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=100.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=102400/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=32

Run status group 0 (all jobs):
WRITE: io=1600.0MB, aggrb=672577KB/s, minb=168144KB/s, maxb=174149KB/s, mint=2352msec, maxt=2436msec

Disk stats (read/write):
zram0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%

	-ss

[global]
size=400m
directory=/mnt/
ioengine=libaio
iodepth=32
direct=1
invalidate=1
numjobs=4
loops=4

[bgreader]
rw=randread

[global]
size=400m
directory=/mnt/
ioengine=libaio
iodepth=32
direct=1
invalidate=1
numjobs=4
loops=5

[bgupdater]
rw=randrw

[global]
size=400m
directory=/mnt/
ioengine=libaio
iodepth=32
direct=1
invalidate=1
numjobs=4
loops=5

[bgwriter]
rw=randwrite

Hello, Minchan:

2015-01-28 16:15 GMT+08:00 Minchan Kim <[email protected]>:

When I/O operation is running, that means the /dev/zram0 is mounted or swaped on. Then the device could not be reset by below code:

    /* Do not reset an active device! */
    if (bdev->bd_holders) {
        ret = -EBUSY;
        goto out;
    }

So the zram->init_lock in I/O path is to check whether the device has been initialized(echo xxx > /sys/block/zram/disk_size).

Is that right?

I do not know much about the lockdep.

enabled the CONFIG_LOCKDEP, But from the test, there is no warning printed. Could you please tell me how this happened?

Thanks.

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for mounted device (w/fs), we see initial (well, it goes up and down many times while we create device, but this is not interesting here) ->bd_holders increment in:
vfs_kern_mount -> mount_bdev -> blkdev_get_by_path -> blkdev_get

and it goes to zero in:
cleanup_mnt -> deactivate_super -> kill_block_super -> blkdev_put

after umount we still have init device. so, *theoretically*, we can see something like

	CPU0				CPU1

umount
reset_store
bdev->bd_holders == 0 mount
... zram_make_request()
zram_reset_device()

w/o zram->init_lock in both zram_reset_device() and zram_make_request() one of CPUs will be a bit sad.

	-ss

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Hello Sergey

2015-01-29 23:12 GMT+08:00 Sergey Senozhatsky <[email protected]>:

Thanks for your explanation.

What does "w/" mean?

In this example, the data stored in zram will be corrupted. Since CPU0 will free meta while CPU1 is using. right?

what does "w/o" mean?

Thanks

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'with fs'

with out ->init_lock protection in this case we have 'free' vs. 'use' race.

'with out'

	-ss

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2015-01-30 16:08 GMT+08:00 Sergey Senozhatsky
<[email protected]>:

Maybe I did not explain clearly. I send a patch about this issue:

https://patchwork.kernel.org/patch/5754041/

Thanks

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[..]

excuse me? explain to me clearly what? my finding and my analysis?

this is the second time in a week that you hijack someone's work and you don't even bother to give any credit to people.

Minchan moved zram_meta_free(meta) out of init_lock here
https://lkml.org/lkml/2015/1/21/29

I proposed to also move zs_free() of meta->handles here
https://lkml.org/lkml/2015/1/21/384

... so what happened then -- you jumped in and sent a patch.
https://lkml.org/lkml/2015/1/24/50

Minchan sent you a hint https://lkml.org/lkml/2015/1/26/471

"the patch is based on my work"!

now, for the last few days we were discussing init_lock and I first expressed my concerns and spoke about 'free' vs. 'use' problem here (but still didn't have enough spare to submit, besides we are in the middle of reset/init/write rework)

https://lkml.org/lkml/2015/1/27/1029

and later here https://lkml.org/lkml/2015/1/29/645

so what happened next? your patch happened next.
with quite familiar problem description

and now you say that I don't understant something in "your analysis"?

stop doing this. this is not how it works.

	-ss

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Hello, Sergey

2015-01-31 19:07 GMT+08:00 Sergey Senozhatsky <[email protected]>:

Sorry, I missed this mail
https://lkml.org/lkml/2015/1/27/1029

That's why I ask questions in this
https://lkml.org/lkml/2015/1/29/580
after Minchan's description.

I thought you wanted move the code block after

       up_write(&zram->init_lock);

And I found the code block can be even encapsulated in zram_meta_free().

That's why I sent:
https://lkml.org/lkml/2015/1/24/50

Sorry, I did not check this mail.

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	-ss

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Right. I overlooked it. I just want to send my patch[2/2] and I thought it would be better ganesh's patch to merge first although it's orthogonal.

Ganesh, I hope you resend this patch with Sergey's suggestion. If you are busy, please tell me. I will do it instead of you.

Kind regards,
Minchan Kim

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Hello, Minchan

2015-01-29 7:17 GMT+08:00 Minchan Kim <[email protected]>:

OK, I will do it today.
Thanks

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