Support sync buffered writes for io-uring

PATCH Superseded Stefan Roesch 4 participants 34 messages Feb 14, 2022 – Feb 16, 2022

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Stefan Roesch

author

2022-02-14 17:44 UTC #0 lore raw

cover Support sync buffered writes for io-uring

This patch series adds support for async buffered writes. Currently io-uring only supports buffered writes in the slow path, by processing them in the io workers. With this patch series it is now possible to support buffered writes in the fast path. To be able to use the fast path the required pages must be in the page cache or they can be loaded with noio. Otherwise they still get punted to the slow path.

If a buffered write request requires more than one page, it is possible that only part of the request can use the fast path, the resst will be completed by the io workers.

Support for async buffered writes:
Patch 1: fs: Add flags parameter to __block_write_begin_int
Add a flag parameter to the function __block_write_begin_int to allow specifying a nowait parameter.

Patch 2: mm: Introduce do_generic_perform_write
Introduce a new do_generic_perform_write function. The function is split off from the existing generic_perform_write() function. It allows to specify an additional flag parameter. This parameter is used to specify the nowait flag.

Patch 3: mm: add noio support in filemap_get_pages
This allows to allocate pages with noio, if a page for async buffered writes is not yet loaded in the page cache.

Patch 4: mm: Add support for async buffered writes
For async buffered writes allocate pages without blocking on the allocation.

Patch 5: fs: split off __alloc_page_buffers function
Split off __alloc_page_buffers() function with new gfp_t parameter.

Patch 6: fs: split off __create_empty_buffers function
Split off __create_empty_buffers() function with new gfp_t parameter.

Patch 7: fs: Add aop_flags parameter to create_page_buffers()
Add aop_flags to create_page_buffers() function. Use atomic allocation for async buffered writes.

Patch 8: fs: add support for async buffered writes
Return -EAGAIN instead of -ENOMEM for async buffered writes. This will cause the write request to be processed by an io worker.

Patch 9: io_uring: add support for async buffered writes
This enables the async buffered writes for block devices in io_uring. Buffered writes are enabled for blocks that are already in the page cache or can be acquired with noio.

Patch 10: io_uring: Add tracepoint for short writes

Support for write throttling of async buffered writes:
Patch 11: sched: add new fields to task_struct
Add two new fields to the task_struct. These fields store the deadline after which writes are no longer throttled.

Patch 12: mm: support write throttling for async buffered writes
This changes the balance_dirty_pages function to take an additonal parameter. When nowait is specified the write throttling code no longer waits synchronously for the deadline to expire. Instead it sets the fields in task_struct. Once the deadline expires the fields are reset.

Patch 13: io_uring: support write throttling for async buffered writes
Adds support to io_uring for write throttling. When the writes are throttled, the write requests are added to the pending io list. Once the write throttling deadline expires, the writes are submitted.

Enable async buffered write support
Patch 14: fs: add flag to support async buffered writes
This sets the flags that enables async buffered writes for block devices.

Testing:
This patch has been tested with xfstests and fio.

Peformance results:
For fio the following results have been obtained with a queue depth of 1 and 4k block size (runtime 600 secs):

sequential writes:
without patch with patch
throughput: 329 Mib/s 1032Mib/s
iops: 82k 264k
slat (nsec) 2332 3340
clat (nsec) 9017 60

CPU util%: 37% 78%

random writes:
without patch with patch
throughput: 307 Mib/s 909Mib/s
iops: 76k 227k
slat (nsec) 2419 3780
clat (nsec) 9934 59

CPU util%: 57% 88%

For an io depth of 1, the new patch improves throughput by close to 3 times and also the latency is considerably reduced. To achieve the same or better performance with the exisiting code an io depth of 4 is required.

Especially for mixed workloads this is a considerable improvement.

Stefan Roesch (14):
fs: Add flags parameter to __block_write_begin_int
mm: Introduce do_generic_perform_write
mm: add noio support in filemap_get_pages
mm: Add support for async buffered writes
fs: split off __alloc_page_buffers function
fs: split off __create_empty_buffers function
fs: Add aop_flags parameter to create_page_buffers()
fs: add support for async buffered writes
io_uring: add support for async buffered writes
io_uring: Add tracepoint for short writes
sched: add new fields to task_struct
mm: support write throttling for async buffered writes
io_uring: support write throttling for async buffered writes
block: enable async buffered writes for block devices.

 block/fops.c                    |   5 +-
 fs/buffer.c                     | 103 ++++++++++++++++---------
 fs/internal.h                   |   3 +-
 fs/io_uring.c                   | 130 +++++++++++++++++++++++++++++---
 fs/iomap/buffered-io.c          |   4 +-
 fs/read_write.c                 |   3 +-
 include/linux/fs.h              |   4 +
 include/linux/sched.h           |   3 +
 include/linux/writeback.h       |   1 +
 include/trace/events/io_uring.h |  25 ++++++
 kernel/fork.c                   |   1 +
 mm/filemap.c                    |  34 +++++++--
 mm/folio-compat.c               |   4 +
 mm/page-writeback.c             |  54 +++++++++----
 14 files changed, 298 insertions(+), 76 deletions(-)

base-commit: f1baf68e1383f6ed93eb9cff2866d46562607a43

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #1 lore raw

PATCH 1/14 fs: Add flags parameter to __block_write_begin_int

This adds a flags parameter to the __begin_write_begin_int() function. This allows to pass flags down the stack.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c            | 7 ++++---
 fs/internal.h          | 3 ++-
 fs/iomap/buffered-io.c | 4 ++--
 3 files changed, 8 insertions(+), 6 deletions(-)

fs/buffer.c +4 -3

index 8e112b6bd371..6e6a69a12eed 100644
@@ -1970,7 +1970,8 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 }
 
 int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
-		get_block_t *get_block, const struct iomap *iomap)
+			get_block_t *get_block, const struct iomap *iomap,
+			unsigned int flags)
 {
 	unsigned from = pos & (PAGE_SIZE - 1);
 	unsigned to = from + len;

@@ -2058,7 +2059,7 @@ int __block_write_begin(struct page *page, loff_t pos, unsigned len,
 		get_block_t *get_block)
 {
 	return __block_write_begin_int(page_folio(page), pos, len, get_block,
-				       NULL);
+				       NULL, 0);
 }
 EXPORT_SYMBOL(__block_write_begin);

@@ -2118,7 +2119,7 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
 	if (!page)
 		return -ENOMEM;
 
-	status = __block_write_begin(page, pos, len, get_block);
+	status = __block_write_begin_int(page_folio(page), pos, len, get_block, NULL, flags);
 	if (unlikely(status)) {
 		unlock_page(page);
 		put_page(page);

fs/internal.h +2 -1

index 8590c973c2f4..7432df23f3ce 100644
@@ -38,7 +38,8 @@ static inline int emergency_thaw_bdev(struct super_block *sb)
  * buffer.c
  */
 int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
-		get_block_t *get_block, const struct iomap *iomap);
+			get_block_t *get_block, const struct iomap *iomap,
+			unsigned int flags);
 
 /*
  * char_dev.c

fs/iomap/buffered-io.c +2 -2

index 6c51a75d0be6..47c519952725 100644
@@ -646,7 +646,7 @@ static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 	if (srcmap->type == IOMAP_INLINE)
 		status = iomap_write_begin_inline(iter, folio);
 	else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
-		status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
+		status = __block_write_begin_int(folio, pos, len, NULL, srcmap, 0);
 	else
 		status = __iomap_write_begin(iter, pos, len, folio);

@@ -979,7 +979,7 @@ static loff_t iomap_folio_mkwrite_iter(struct iomap_iter *iter,
 
 	if (iter->iomap.flags & IOMAP_F_BUFFER_HEAD) {
 		ret = __block_write_begin_int(folio, iter->pos, length, NULL,
-					      &iter->iomap);
+					      &iter->iomap, 0);
 		if (ret)
 			return ret;
 		block_commit_write(&folio->page, 0, length);

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-14 20:56 UTC #2 lore raw

Re: [PATCH v1 01/14] fs: Add flags parameter to __block_write_begin_int

Quoted 2 lines · Stefan Roesch

This adds a flags parameter to the __begin_write_begin_int() function. This allows to pass flags down the stack.

In general, I am not in favour of more AOP_FLAG uses. I'd prefer to remove the two that we do have (reiserfs is the only user of AOP_FLAG_CONT_EXPAND and AOP_FLAG_NOFS can usually be replaced by passing in gfp_t flags).

Stefan Roesch

author

2022-02-16 18:31 UTC #3 lore raw

Re: [PATCH v1 01/14] fs: Add flags parameter to __block_write_begin_int

I don't think that gfp flags are a great fit here. We only want to pass in a nowait flag and this does not map nicely to a gfp flag.

Instead of passing in a flag parameter we can also pass in a bool parameter, however that has its limitations as it can't be extended in the future.

Quoted 8 lines · Matthew Wilcox

Quoted 2 lines · Stefan Roesch
This adds a flags parameter to the __begin_write_begin_int() function. This allows to pass flags down the stack.
In general, I am not in favour of more AOP_FLAG uses. I'd prefer to remove the two that we do have (reiserfs is the only user of AOP_FLAG_CONT_EXPAND and AOP_FLAG_NOFS can usually be replaced by passing in gfp_t flags).

Matthew Wilcox

maintainer

2022-02-16 18:35 UTC #4 lore raw

Re: [PATCH v1 01/14] fs: Add flags parameter to __block_write_begin_int

Quoted 5 lines · Stefan Roesch

I don't think that gfp flags are a great fit here. We only want to pass in a nowait flag and this does not map nicely to a gfp flag.
Instead of passing in a flag parameter we can also pass in a bool parameter, however that has its limitations as it can't be extended in the future.

if you're just going to copy and paste this inanity into every reply to me, let's just say hard NAK to every patch from you for now on?

Stefan Roesch

author

2022-02-14 17:44 UTC #5 lore raw

PATCH 2/14 mm: Introduce do_generic_perform_write

In reply to Stefan Roesch

This splits off the do generic_perform_write() function, so an additional flags parameter can be specified. It uses the new flag parameter to support async buffered writes.

Signed-off-by Stefan Roesch <[email protected]>

---
 include/linux/fs.h |  1 +
 mm/filemap.c       | 20 +++++++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

include/linux/fs.h +1 -0

index e2d892b201b0..e62dba6ed453 100644
@@ -278,6 +278,7 @@ enum positive_aop_returns {
 #define AOP_FLAG_NOFS			0x0002 /* used by filesystem to direct
 						* helper code (eg buffer layer)
 						* to clear GFP_FS from alloc */
+#define AOP_FLAGS_NOWAIT		0x0004 /* async nowait buffered writes */
 
 /*
  * oh the beauties of C type declarations.

mm/filemap.c +15 -5

index ad8c39d90bf9..d2fb817c0845 100644
@@ -3725,14 +3725,13 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
 }
 EXPORT_SYMBOL(generic_file_direct_write);
 
-ssize_t generic_perform_write(struct file *file,
-				struct iov_iter *i, loff_t pos)
+static ssize_t do_generic_perform_write(struct file *file, struct iov_iter *i,
+					loff_t pos, int flags)
 {
 	struct address_space *mapping = file->f_mapping;
 	const struct address_space_operations *a_ops = mapping->a_ops;
 	long status = 0;
 	ssize_t written = 0;
-	unsigned int flags = 0;
 
 	do {
 		struct page *page;

@@ -3801,6 +3800,12 @@ ssize_t generic_perform_write(struct file *file,
 
 	return written ? written : status;
 }
+
+ssize_t generic_perform_write(struct file *file,
+				struct iov_iter *i, loff_t pos)
+{
+	return do_generic_perform_write(file, i, pos, 0);
+}
 EXPORT_SYMBOL(generic_perform_write);
 
 /**

@@ -3832,6 +3837,10 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	ssize_t		written = 0;
 	ssize_t		err;
 	ssize_t		status;
+	int             flags = 0;
+
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		flags |= AOP_FLAGS_NOWAIT;
 
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = inode_to_bdi(inode);

@@ -3857,7 +3866,8 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
 			goto out;
 
-		status = generic_perform_write(file, from, pos = iocb->ki_pos);
+		status = do_generic_perform_write(file, from, pos = iocb->ki_pos, flags);
+
 		/*
 		 * If generic_perform_write() returned a synchronous error
 		 * then we want to return the number of bytes which were

@@ -3889,7 +3899,7 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			 */
 		}
 	} else {
-		written = generic_perform_write(file, from, iocb->ki_pos);
+		written = do_generic_perform_write(file, from, iocb->ki_pos, flags);
 		if (likely(written > 0))
 			iocb->ki_pos += written;
 	}

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-14 20:56 UTC #6 lore raw

Re: [PATCH v1 02/14] mm: Introduce do_generic_perform_write

Quoted 3 lines · Stefan Roesch

This splits off the do generic_perform_write() function, so an additional flags parameter can be specified. It uses the new flag parameter to support async buffered writes.

It would seem simpler to pass the iocb pointer to generic_perform_write() (in place of the struct file pointer) instead of inventing a new flag.

Stefan Roesch

author

2022-02-14 17:44 UTC #7 lore raw

PATCH 3/14 mm: add noio support in filemap_get_pages

In reply to Stefan Roesch

This adds noio support for async buffered writes in filemap_get_pages. The idea is to handle the failure gracefully and return -EAGAIN if we can't get the memory quickly.

Signed-off-by Stefan Roesch <[email protected]>

---
 mm/filemap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

mm/filemap.c +6 -1

index d2fb817c0845..0ff4278c3961 100644
@@ -2591,10 +2591,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 		filemap_get_read_batch(mapping, index, last_index, fbatch);
 	}
 	if (!folio_batch_count(fbatch)) {
+		unsigned int pflags;
+
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
-			return -EAGAIN;
+			pflags = memalloc_noio_save();
 		err = filemap_create_folio(filp, mapping,
 				iocb->ki_pos >> PAGE_SHIFT, fbatch);
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
+			memalloc_noio_restore(pflags);
+
 		if (err == AOP_TRUNCATED_PAGE)
 			goto retry;
 		return err;

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-14 18:08 UTC #8 lore raw

Re: [PATCH v1 03/14] mm: add noio support in filemap_get_pages

Quoted 3 lines · Stefan Roesch

This adds noio support for async buffered writes in filemap_get_pages. The idea is to handle the failure gracefully and return -EAGAIN if we can't get the memory quickly.

But it doesn't return -EAGAIN?

        folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
        if (!folio)
                return -ENOMEM;

Quoted 16 lines

Signed-off-by Stefan Roesch <[email protected]>

---
 mm/filemap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

mm/filemap.c +2 -0

index d2fb817c0845..0ff4278c3961 100644
@@ -2591,10 +2591,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 		filemap_get_read_batch(mapping, index, last_index, fbatch);
 	}
 	if (!folio_batch_count(fbatch)) {
+		unsigned int pflags;
+
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))

mm/filemap.c static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, · line 2605

Quoted 10 lines

mm/filemap.c +4 -1

-			return -EAGAIN;
+			pflags = memalloc_noio_save();
 		err = filemap_create_folio(filp, mapping,
 				iocb->ki_pos >> PAGE_SHIFT, fbatch);
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
+			memalloc_noio_restore(pflags);
+
 		if (err == AOP_TRUNCATED_PAGE)
 			goto retry;
 		return err;

I would also not expect the memalloc_noio_save/restore calls to be here. Surely they should be at the top of the call chain where IOCB_NOWAIT/IOCB_WAITQ are set?

Stefan Roesch

author

2022-02-16 18:27 UTC #9 lore raw

Re: [PATCH v1 03/14] mm: add noio support in filemap_get_pages

Quoted 33 lines · Matthew Wilcox

Quoted 3 lines · Stefan Roesch

This adds noio support for async buffered writes in filemap_get_pages. The idea is to handle the failure gracefully and return -EAGAIN if we can't get the memory quickly.

But it doesn't return -EAGAIN?

        folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
        if (!folio)
                return -ENOMEM;

Quoted 22 lines

Signed-off-by Stefan Roesch <[email protected]>

---
 mm/filemap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

mm/filemap.c +5 -1

index d2fb817c0845..0ff4278c3961 100644
@@ -2591,10 +2591,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 		filemap_get_read_batch(mapping, index, last_index, fbatch);
 	}
 	if (!folio_batch_count(fbatch)) {
+		unsigned int pflags;
+
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
-			return -EAGAIN;
+			pflags = memalloc_noio_save();
 		err = filemap_create_folio(filp, mapping,
 				iocb->ki_pos >> PAGE_SHIFT, fbatch);
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
+			memalloc_noio_restore(pflags);

Quoted 8 lines

mm/filemap.c static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, · line 2605
Quoted 4 lines
mm/filemap.c +1 -0
+
 		if (err == AOP_TRUNCATED_PAGE)
 			goto retry;
 		return err;
I would also not expect the memalloc_noio_save/restore calls to be here. Surely they should be at the top of the call chain where IOCB_NOWAIT/IOCB_WAITQ are set?

This patch will be removed from the next version of the patch series.

Matthew Wilcox

maintainer

2022-02-14 20:57 UTC #10 lore raw

Re: [PATCH v1 03/14] mm: add noio support in filemap_get_pages

In reply to Stefan Roesch

Quoted 3 lines · Stefan Roesch

This adds noio support for async buffered writes in filemap_get_pages. The idea is to handle the failure gracefully and return -EAGAIN if we can't get the memory quickly.

I don't understand why this helps you. filemap_get_pages() is for reads, not writes.

Stefan Roesch

author

2022-02-16 18:26 UTC #11 lore raw

Re: [PATCH v1 03/14] mm: add noio support in filemap_get_pages

This patch will be removed from the next version.

Quoted 7 lines · Matthew Wilcox

Quoted 3 lines · Stefan Roesch
This adds noio support for async buffered writes in filemap_get_pages. The idea is to handle the failure gracefully and return -EAGAIN if we can't get the memory quickly.
I don't understand why this helps you. filemap_get_pages() is for reads, not writes.

Stefan Roesch

author

2022-02-14 17:44 UTC #12 lore raw

PATCH 4/14 mm: Add support for async buffered writes

In reply to Stefan Roesch

This adds support for async buffered writes in the mm layer. When the AOP_FLAGS_BUF_WASYNC flag is set, if the page is not already loaded, the page gets created without blocking on the allocation.

Signed-off-by Stefan Roesch <[email protected]>

---
 mm/filemap.c      | 5 +++++
 mm/folio-compat.c | 4 ++++
 2 files changed, 9 insertions(+)

mm/filemap.c +5 -0

index 0ff4278c3961..19065ad95a4c 100644
@@ -42,6 +42,7 @@
 #include <linux/ramfs.h>
 #include <linux/page_idle.h>
 #include <linux/migrate.h>
+#include <linux/sched/mm.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 #include "internal.h"

@@ -1986,6 +1987,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			gfp |= __GFP_WRITE;
 		if (fgp_flags & FGP_NOFS)
 			gfp &= ~__GFP_FS;
+		if (fgp_flags & FGP_NOWAIT) {
+			gfp |= GFP_ATOMIC;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		}
 
 		folio = filemap_alloc_folio(gfp, 0);
 		if (!folio)

mm/folio-compat.c +4 -0

index 749555a232a8..a1d05509b29f 100644
@@ -136,6 +136,10 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 
 	if (flags & AOP_FLAG_NOFS)
 		fgp_flags |= FGP_NOFS;
+
+	if (flags & AOP_FLAGS_NOWAIT)
+		fgp_flags |= FGP_NOWAIT;
+
 	return pagecache_get_page(mapping, index, fgp_flags,
 			mapping_gfp_mask(mapping));
 }

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-14 20:53 UTC #13 lore raw

Re: [PATCH v1 04/14] mm: Add support for async buffered writes

mm/filemap.c struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index, · line 1995

Quoted 10 lines · Stefan Roesch

mm/filemap.c +4 -0

@@ -1986,6 +1987,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			gfp |= __GFP_WRITE;
 		if (fgp_flags & FGP_NOFS)
 			gfp &= ~__GFP_FS;
+		if (fgp_flags & FGP_NOWAIT) {
+			gfp |= GFP_ATOMIC;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		}
 
 		folio = filemap_alloc_folio(gfp, 0);

No. FGP_NOWAIT means "Don't block on page lock". You can't redefine it to mean "Use GFP_ATOMIC" without changing all the existing callers. (Do not change the existing callers).

__filemap_get_folio() already takes a gfp_t. There's no need for this.

Stefan Roesch

author

2022-02-14 17:44 UTC #14 lore raw

PATCH 5/14 fs: split off __alloc_page_buffers function

In reply to Stefan Roesch

This splits off the __alloc_page_buffers() function from the alloc_page_buffers_function(). In addition it adds a gfp_t parameter, so the caller can specify the allocation flags.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

fs/buffer.c +22 ~~-15~~

index 6e6a69a12eed..a1986f95a39a 100644
@@ -802,26 +802,13 @@ int remove_inode_buffers(struct inode *inode)
 	return ret;
 }
 
-/*
- * Create the appropriate buffers when given a page for data area and
- * the size of each buffer.. Use the bh->b_this_page linked list to
- * follow the buffers created.  Return NULL if unable to create more
- * buffers.
- *
- * The retry flag is used to differentiate async IO (paging, swapping)
- * which may not fail from ordinary buffer allocations.
- */
-struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
-		bool retry)
+struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
+		gfp_t gfp)
 {
 	struct buffer_head *bh, *head;
-	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
 	long offset;
 	struct mem_cgroup *memcg, *old_memcg;
 
-	if (retry)
-		gfp |= __GFP_NOFAIL;
-
 	/* The page lock pins the memcg */
 	memcg = page_memcg(page);
 	old_memcg = set_active_memcg(memcg);

@@ -859,6 +846,26 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 
 	goto out;
 }
+
+/*
+ * Create the appropriate buffers when given a page for data area and
+ * the size of each buffer.. Use the bh->b_this_page linked list to
+ * follow the buffers created.  Return NULL if unable to create more
+ * buffers.
+ *
+ * The retry flag is used to differentiate async IO (paging, swapping)
+ * which may not fail from ordinary buffer allocations.
+ */
+struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
+		bool retry)
+{
+	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+	if (retry)
+		gfp |= __GFP_NOFAIL;
+
+	return __alloc_page_buffers(page, size, gfp);
+}
 EXPORT_SYMBOL_GPL(alloc_page_buffers);
 
 static inline void

Signature · 1 line

2.30.2

kernel test robot

build bot

2022-02-14 22:46 UTC #15 lore raw

Re: [PATCH v1 05/14] fs: split off __alloc_page_buffers function

Thank you for the patch! Perhaps something to improve:

Hi Stefan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on f1baf68e1383f6ed93eb9cff2866d46562607a43]

url:    https://github.com/0day-ci/linux/commits/Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908
base:   f1baf68e1383f6ed93eb9cff2866d46562607a43
config: i386-randconfig-a016-20220214 (https://download.01.org/0day-ci/archive/20220215/202202150646.hLANces3-lkp(a)intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

reproduce (this is a W=1 build):
# https://github.com/0day-ci/linux/commit/e8b24c1ab111c127cbe1daaac3b607c626fb03a8
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908 git checkout e8b24c1ab111c127cbe1daaac3b607c626fb03a8
# save the config file to linux build tree
mkdir build_dir
make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate

Reported-by kernel test robot <[email protected]>

All warnings (new ones prefixed by >>):

>> fs/buffer.c:805:21: warning: no previous prototype for '__alloc_page_buffers' [-Wmissing-prototypes]

805 | struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
| ^~~~~~~~~~~~~~~~~~~~

vim +/__alloc_page_buffers +805 fs/buffer.c

804

 > 805	struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,

806 gfp_t gfp)
807 {
808 struct buffer_head *bh, *head;
809 long offset;
810 struct mem_cgroup *memcg, *old_memcg;
811
812 /* The page lock pins the memcg */
813 memcg = page_memcg(page);
814 old_memcg = set_active_memcg(memcg);
815
816 head = NULL;
817 offset = PAGE_SIZE;
818 while ((offset -= size) >= 0) {
819 bh = alloc_buffer_head(gfp);
820 if (!bh)
821 goto no_grow;
822
823 bh->b_this_page = head;
824 bh->b_blocknr = -1;
825 head = bh;
826
827 bh->b_size = size;
828
829 /* Link the buffer to its page */
830 set_bh_page(bh, page, offset);
831 }
832 out:
833 set_active_memcg(old_memcg);
834 return head;
835 /*
836 * In case anything failed, we just free everything we got.
837 */
838 no_grow:
839 if (head) {
840 do {
841 bh = head;
842 head = head->b_this_page;
843 free_buffer_head(bh);
844 } while (head);
845 }
846
847 goto out;
848 }
849

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

kernel test robot

build bot

2022-02-14 23:27 UTC #16 lore raw

Re: [PATCH v1 05/14] fs: split off __alloc_page_buffers function

In reply to Stefan Roesch

Thank you for the patch! Perhaps something to improve:

Hi Stefan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on f1baf68e1383f6ed93eb9cff2866d46562607a43]

url:    https://github.com/0day-ci/linux/commits/Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908
base:   f1baf68e1383f6ed93eb9cff2866d46562607a43
config: arm-s5pv210_defconfig (https://download.01.org/0day-ci/archive/20220215/202202150743.R5ymlf5z-lkp(a)intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project ea071884b0cc7210b3cc5fe858f0e892a779a23b)

reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
# install arm cross compiling tool for clang build
# apt-get install binutils-arm-linux-gnueabi
# https://github.com/0day-ci/linux/commit/e8b24c1ab111c127cbe1daaac3b607c626fb03a8
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908 git checkout e8b24c1ab111c127cbe1daaac3b607c626fb03a8
# save the config file to linux build tree
mkdir build_dir
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate

Reported-by kernel test robot <[email protected]>

All warnings (new ones prefixed by >>):

>> fs/buffer.c:805:21: warning: no previous prototype for function '__alloc_page_buffers' [-Wmissing-prototypes]
   struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
                       ^

fs/buffer.c:805:1: note: declare 'static' if the function is not intended to be used outside of this translation unit struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
^
static
1 warning generated.

vim +/__alloc_page_buffers +805 fs/buffer.c

804

 > 805	struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

kernel test robot

build bot

2022-02-15 02:40 UTC #17 lore raw

[RFC PATCH] fs: __alloc_page_buffers() can be static

In reply to Stefan Roesch

fs/buffer.c:805:20: warning: symbol '__alloc_page_buffers' was not declared. Should it be static?

fs/buffer.c:805:20: warning: symbol '__alloc_page_buffers' was not declared. Should it be static?

Reported-by kernel test robot <[email protected]>

Signed-off-by kernel test robot <[email protected]>

---
 fs/buffer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

fs/buffer.c +1 -1

index a1986f95a39a0..19a4ab1f61686 100644
@@ -802,7 +802,7 @@ int remove_inode_buffers(struct inode *inode)
 	return ret;
 }
 
-struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
+static struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
 		gfp_t gfp)
 {
 	struct buffer_head *bh, *head;

kernel test robot

build bot

2022-02-15 02:41 UTC #18 lore raw

Re: [PATCH v1 05/14] fs: split off __alloc_page_buffers function

In reply to Stefan Roesch

Thank you for the patch! Perhaps something to improve:

Hi Stefan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on f1baf68e1383f6ed93eb9cff2866d46562607a43]

url:    https://github.com/0day-ci/linux/commits/Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908
base:   f1baf68e1383f6ed93eb9cff2866d46562607a43
config: i386-randconfig-s002-20220214 (https://download.01.org/0day-ci/archive/20220215/202202151030.Z3rVrN17-lkp(a)intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-dirty
        # https://github.com/0day-ci/linux/commit/e8b24c1ab111c127cbe1daaac3b607c626fb03a8
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Stefan-Roesch/Support-sync-buffered-writes-for-io-uring/20220215-014908
        git checkout e8b24c1ab111c127cbe1daaac3b607c626fb03a8
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate

Reported-by kernel test robot <[email protected]>

sparse warnings: (new ones prefixed by >>)

>> fs/buffer.c:805:20: sparse: sparse: symbol '__alloc_page_buffers' was not declared. Should it be static?

Please review and possibly fold the followup patch.

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

Stefan Roesch

author

2022-02-14 17:44 UTC #19 lore raw

PATCH 6/14 fs: split off __create_empty_buffers function

In reply to Stefan Roesch

This splits off the function __create_empty_buffers() from the function create_empty_buffers. The __create_empty_buffers has an additional gfp parameter. This allows the caller to specify the allocation properties.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

fs/buffer.c +14 -8

index a1986f95a39a..948505480b43 100644
@@ -1554,17 +1554,12 @@ void block_invalidatepage(struct page *page, unsigned int offset,
 EXPORT_SYMBOL(block_invalidatepage);
 
 
-/*
- * We attach and possibly dirty the buffers atomically wrt
- * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
- * is already excluded via the page lock.
- */
-void create_empty_buffers(struct page *page,
-			unsigned long blocksize, unsigned long b_state)
+static void __create_empty_buffers(struct page *page, unsigned long blocksize,
+				unsigned long b_state, gfp_t gfp)
 {
 	struct buffer_head *bh, *head, *tail;
 
-	head = alloc_page_buffers(page, blocksize, true);
+	head = __alloc_page_buffers(page, blocksize, gfp);
 	bh = head;
 	do {
 		bh->b_state |= b_state;

@@ -1587,6 +1582,17 @@ void create_empty_buffers(struct page *page,
 	attach_page_private(page, head);
 	spin_unlock(&page->mapping->private_lock);
 }
+/*
+ * We attach and possibly dirty the buffers atomically wrt
+ * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
+ * is already excluded via the page lock.
+ */
+void create_empty_buffers(struct page *page,
+			unsigned long blocksize, unsigned long b_state)
+{
+	return __create_empty_buffers(page, blocksize, b_state,
+				GFP_NOFS | __GFP_ACCOUNT | __GFP_NOFAIL);
+}
 EXPORT_SYMBOL(create_empty_buffers);
 
 /**

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #20 lore raw

PATCH 7/14 fs: Add aop_flags parameter to create_page_buffers()

In reply to Stefan Roesch

This adds the aop_flags parameter to the create_page_buffers function. When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are enabled.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

fs/buffer.c +21 -7

index 948505480b43..5e3067173580 100644
@@ -1682,13 +1682,27 @@ static inline int block_size_bits(unsigned int blocksize)
 	return ilog2(blocksize);
 }
 
-static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+static struct buffer_head *create_page_buffers(struct page *page,
+					struct inode *inode,
+					unsigned int b_state,
+					unsigned int aop_flags)
 {
 	BUG_ON(!PageLocked(page));
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
-				     b_state);
+	if (!page_has_buffers(page)) {
+		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+		if (aop_flags & AOP_FLAGS_NOWAIT) {
+			gfp |= GFP_ATOMIC | __GFP_NOWARN;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		} else {
+			gfp |= __GFP_NOFAIL;
+		}
+
+		__create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
+				     b_state, gfp);
+	}
+
 	return page_buffers(page);
 }

@@ -1734,7 +1748,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 	int write_flags = wbc_to_write_flags(wbc);
 
 	head = create_page_buffers(page, inode,
-					(1 << BH_Dirty)|(1 << BH_Uptodate));
+					(1 << BH_Dirty)|(1 << BH_Uptodate), 0);
 
 	/*
 	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers

@@ -2000,7 +2014,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 	BUG_ON(to > PAGE_SIZE);
 	BUG_ON(from > to);
 
-	head = create_page_buffers(&folio->page, inode, 0);
+	head = create_page_buffers(&folio->page, inode, 0, flags);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

@@ -2280,7 +2294,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
 	int nr, i;
 	int fully_mapped = 1;
 
-	head = create_page_buffers(page, inode, 0);
+	head = create_page_buffers(page, inode, 0, 0);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-14 18:14 UTC #21 lore raw

Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

Quoted 4 lines · Stefan Roesch

This adds the aop_flags parameter to the create_page_buffers function. When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are enabled.

Why is this better than passing in gfp flags directly?

Quoted 71 lines

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

fs/buffer.c +21 -7

index 948505480b43..5e3067173580 100644
@@ -1682,13 +1682,27 @@ static inline int block_size_bits(unsigned int blocksize)
 	return ilog2(blocksize);
 }
 
-static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+static struct buffer_head *create_page_buffers(struct page *page,
+					struct inode *inode,
+					unsigned int b_state,
+					unsigned int aop_flags)
 {
 	BUG_ON(!PageLocked(page));
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
-				     b_state);
+	if (!page_has_buffers(page)) {
+		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+		if (aop_flags & AOP_FLAGS_NOWAIT) {
+			gfp |= GFP_ATOMIC | __GFP_NOWARN;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		} else {
+			gfp |= __GFP_NOFAIL;
+		}
+
+		__create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
+				     b_state, gfp);
+	}
+
 	return page_buffers(page);
 }

@@ -1734,7 +1748,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 	int write_flags = wbc_to_write_flags(wbc);
 
 	head = create_page_buffers(page, inode,
-					(1 << BH_Dirty)|(1 << BH_Uptodate));
+					(1 << BH_Dirty)|(1 << BH_Uptodate), 0);
 
 	/*
 	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers

@@ -2000,7 +2014,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 	BUG_ON(to > PAGE_SIZE);
 	BUG_ON(from > to);
 
-	head = create_page_buffers(&folio->page, inode, 0);
+	head = create_page_buffers(&folio->page, inode, 0, flags);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

@@ -2280,7 +2294,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
 	int nr, i;
 	int fully_mapped = 1;
 
-	head = create_page_buffers(page, inode, 0);
+	head = create_page_buffers(page, inode, 0, 0);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-16 18:31 UTC #22 lore raw

Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

Quoted 8 lines · Matthew Wilcox

Quoted 4 lines · Stefan Roesch
This adds the aop_flags parameter to the create_page_buffers function. When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are enabled.
Why is this better than passing in gfp flags directly?

I don't think that gfp flags are a great fit here. We only want to pass in a nowait flag and this does not map nicely to a gfp flag.

Instead of passing in a flag parameter we can also pass in a bool parameter, however that has its limitations as it can't be extended in the future.

Quoted 71 lines

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

fs/buffer.c +21 -7

index 948505480b43..5e3067173580 100644
@@ -1682,13 +1682,27 @@ static inline int block_size_bits(unsigned int blocksize)
 	return ilog2(blocksize);
 }
 
-static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+static struct buffer_head *create_page_buffers(struct page *page,
+					struct inode *inode,
+					unsigned int b_state,
+					unsigned int aop_flags)
 {
 	BUG_ON(!PageLocked(page));
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
-				     b_state);
+	if (!page_has_buffers(page)) {
+		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+		if (aop_flags & AOP_FLAGS_NOWAIT) {
+			gfp |= GFP_ATOMIC | __GFP_NOWARN;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		} else {
+			gfp |= __GFP_NOFAIL;
+		}
+
+		__create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
+				     b_state, gfp);
+	}
+
 	return page_buffers(page);
 }

@@ -1734,7 +1748,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 	int write_flags = wbc_to_write_flags(wbc);
 
 	head = create_page_buffers(page, inode,
-					(1 << BH_Dirty)|(1 << BH_Uptodate));
+					(1 << BH_Dirty)|(1 << BH_Uptodate), 0);
 
 	/*
 	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers

@@ -2000,7 +2014,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 	BUG_ON(to > PAGE_SIZE);
 	BUG_ON(from > to);
 
-	head = create_page_buffers(&folio->page, inode, 0);
+	head = create_page_buffers(&folio->page, inode, 0, flags);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

@@ -2280,7 +2294,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
 	int nr, i;
 	int fully_mapped = 1;
 
-	head = create_page_buffers(page, inode, 0);
+	head = create_page_buffers(page, inode, 0, 0);
 	blocksize = head->b_size;
 	bbits = block_size_bits(blocksize);

Signature · 1 line

2.30.2

Matthew Wilcox

maintainer

2022-02-16 18:34 UTC #23 lore raw

Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

Quoted 7 lines · Stefan Roesch

Quoted 6 lines · Matthew Wilcox
Quoted 4 lines · Stefan Roesch
This adds the aop_flags parameter to the create_page_buffers function. When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are enabled.

Quoted 5 lines

Quoted 2 lines
Why is this better than passing in gfp flags directly?
I don't think that gfp flags are a great fit here. We only want to pass in a nowait flag and this does not map nicely to a gfp flag.

... what? The only thing you do with this flag is use it to choose some gfp flags. Pass those gfp flags in directly.

Quoted 8 lines

Quoted 8 lines
fs/buffer.c static inline int block_size_bits(unsigned int blocksize) · line 1700
Quoted 8 lines
fs/buffer.c +8 -0
+		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+		if (aop_flags & AOP_FLAGS_NOWAIT) {
+			gfp |= GFP_ATOMIC | __GFP_NOWARN;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		} else {
+			gfp |= __GFP_NOFAIL;
+		}

The flags you've chosen here are also bonkers, but I'm not sure that it's worth explaining to you why if you're this resistant to making obvious corrections to your patches.

Stefan Roesch

author

2022-02-16 18:35 UTC #24 lore raw

Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

Quoted 17 lines · Matthew Wilcox

Quoted 7 lines · Stefan Roesch
Quoted 6 lines · Matthew Wilcox
Quoted 4 lines · Stefan Roesch
This adds the aop_flags parameter to the create_page_buffers function. When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are enabled.
Quoted 5 lines
Quoted 2 lines
Why is this better than passing in gfp flags directly?
I don't think that gfp flags are a great fit here. We only want to pass in a nowait flag and this does not map nicely to a gfp flag.
... what? The only thing you do with this flag is use it to choose some gfp flags. Pass those gfp flags in directly.

Quoted 12 lines

Quoted 8 lines
Quoted 8 lines
fs/buffer.c static inline int block_size_bits(unsigned int blocksize) · line 1700
Quoted 8 lines
fs/buffer.c +8 -0
+		gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+		if (aop_flags & AOP_FLAGS_NOWAIT) {
+			gfp |= GFP_ATOMIC | __GFP_NOWARN;
+			gfp &= ~__GFP_DIRECT_RECLAIM;
+		} else {
+			gfp |= __GFP_NOFAIL;
+		}
The flags you've chosen here are also bonkers, but I'm not sure that it's worth explaining to you why if you're this resistant to making obvious corrections to your patches.

Sorry my comment was for patch 1 not patch 7.

Stefan Roesch

author

2022-02-14 17:44 UTC #25 lore raw

PATCH 8/14 fs: add support for async buffered writes

In reply to Stefan Roesch

This adds support for the AOP_FLAGS_BUF_WASYNC flag to the fs layer. If a page that is required for writing is not in the page cache, it returns EAGAIN instead of ENOMEM.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/buffer.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

fs/buffer.c +8 -1

index 5e3067173580..140f57c1cbdd 100644
@@ -2069,6 +2069,10 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 			*wait_bh++=bh;
 		}
 	}
+
+	/* No wait specified, don't wait for reads to complete. */
+	if (!err && wait_bh > wait && (flags & AOP_FLAGS_NOWAIT))
+		return -EAGAIN;
 	/*
 	 * If we issued read requests - let them complete.
 	 */

@@ -2143,8 +2147,11 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
 	int status;
 
 	page = grab_cache_page_write_begin(mapping, index, flags);
-	if (!page)
+	if (!page) {
+		if (flags & AOP_FLAGS_NOWAIT)
+			return -EAGAIN;
 		return -ENOMEM;
+	}
 
 	status = __block_write_begin_int(page_folio(page), pos, len, get_block, NULL, flags);
 	if (unlikely(status)) {

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #26 lore raw

PATCH 9/14 io_uring: add support for async buffered writes

In reply to Stefan Roesch

This enables the async buffered writes for block devices in io_uring. Buffered writes are enabled for blocks that are already in the page cache or can be acquired with noio.

It is possible that a write request cannot be completely fullfilled (short write). In that case the request is punted and sent to the io workers to be completed. Before submitting the request to the io workers, the request is updated with how much has already been written.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/io_uring.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

fs/io_uring.c +24 -5

index 2e04f718319d..76b1ff602470 100644
@@ -3615,7 +3615,7 @@ static inline int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
 		return -EINVAL;
 }
 
-static bool need_read_all(struct io_kiocb *req)
+static bool need_complete_io(struct io_kiocb *req)
 {
 	return req->flags & REQ_F_ISREG ||
 		S_ISBLK(file_inode(req->file)->i_mode);

@@ -3679,7 +3679,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 	} else if (ret == -EIOCBQUEUED) {
 		goto out_free;
 	} else if (ret == req->result || ret <= 0 || !force_nonblock ||
-		   (req->flags & REQ_F_NOWAIT) || !need_read_all(req)) {
+		   (req->flags & REQ_F_NOWAIT) || !need_complete_io(req)) {
 		/* read all, failed, already did sync or don't want to retry */
 		goto done;
 	}

@@ -3777,9 +3777,10 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		if (unlikely(!io_file_supports_nowait(req)))
 			goto copy_iov;
 
-		/* file path doesn't support NOWAIT for non-direct_IO */
-		if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT) &&
-		    (req->flags & REQ_F_ISREG))
+		/* File path supports NOWAIT for non-direct_IO only for block devices. */
+		if (!(kiocb->ki_flags & IOCB_DIRECT) &&
+			!(kiocb->ki_filp->f_mode & FMODE_BUF_WASYNC) &&
+			(req->flags & REQ_F_ISREG))
 			goto copy_iov;
 
 		kiocb->ki_flags |= IOCB_NOWAIT;

@@ -3831,6 +3832,24 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		/* IOPOLL retry should happen for io-wq threads */
 		if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
 			goto copy_iov;
+
+		if (ret2 != req->result && ret2 >= 0 && need_complete_io(req)) {
+			struct io_async_rw *rw;
+
+			/* This is a partial write. The file pos has already been
+			 * updated, setup the async struct to complete the request
+			 * in the worker. Also update bytes_done to account for
+			 * the bytes already written.
+			 */
+			iov_iter_save_state(&s->iter, &s->iter_state);
+			ret = io_setup_async_rw(req, iovec, s, true);
+
+			rw = req->async_data;
+			if (rw)
+				rw->bytes_done += ret2;
+
+			return ret ? ret : -EAGAIN;
+		}
 done:
 		kiocb_done(req, ret2, issue_flags);
 	} else {

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #27 lore raw

PATCH 10/14 io_uring: Add tracepoint for short writes

In reply to Stefan Roesch

This adds the io_uring_short_write tracepoint to io_uring. A short write is issued if not all pages that are required for a write are in the page cache and the async buffered writes have to return EAGAIN.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/io_uring.c                   |  3 +++
 include/trace/events/io_uring.h | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

fs/io_uring.c +3 -0

index 76b1ff602470..507f28b5b2bb 100644
@@ -3836,6 +3836,9 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		if (ret2 != req->result && ret2 >= 0 && need_complete_io(req)) {
 			struct io_async_rw *rw;
 
+			trace_io_uring_short_write(req->ctx, kiocb->ki_pos - ret2,
+						req->result, ret2);
+
 			/* This is a partial write. The file pos has already been
 			 * updated, setup the async struct to complete the request
 			 * in the worker. Also update bytes_done to account for

include/trace/events/io_uring.h +25 -0

index 7346f0164cf4..ce1cfdf4b015 100644
@@ -558,6 +558,31 @@ TRACE_EVENT(io_uring_req_failed,
 		  (unsigned long long) __entry->pad2, __entry->error)
 );
 
+TRACE_EVENT(io_uring_short_write,
+
+	TP_PROTO(void *ctx, u64 fpos, u64 wanted, u64 got),
+
+	TP_ARGS(ctx, fpos, wanted, got),
+
+	TP_STRUCT__entry(
+		__field(void *,	ctx)
+		__field(u64,	fpos)
+		__field(u64,	wanted)
+		__field(u64,	got)
+	),
+
+	TP_fast_assign(
+		__entry->ctx	= ctx;
+		__entry->fpos	= fpos;
+		__entry->wanted	= wanted;
+		__entry->got	= got;
+	),
+
+	TP_printk("ring %p, fpos %lld, wanted %lld, got %lld",
+			  __entry->ctx, __entry->fpos,
+			  __entry->wanted, __entry->got)
+);
+
 #endif /* _TRACE_IO_URING_H */
 
 /* This part must be outside protection */

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #28 lore raw

PATCH 11/14 sched: add new fields to task_struct

In reply to Stefan Roesch

Add two new fields to the task_struct to support async write throttling.

- One field to store how long writes are throttled: bdp_pause
- The other field to store the number of dirtied pages:
bdp_nr_dirtied_pause

Signed-off-by Stefan Roesch <[email protected]>

---
 include/linux/sched.h | 3 +++
 kernel/fork.c         | 1 +
 2 files changed, 4 insertions(+)

include/linux/sched.h +3 -0

index 75ba8aa60248..97146b7539c5 100644
@@ -1324,6 +1324,9 @@ struct task_struct {
 	/* Start of a write-and-pause period: */
 	unsigned long			dirty_paused_when;
 
+	unsigned long			bdp_pause;
+	int				bdp_nr_dirtied_pause;
+
 #ifdef CONFIG_LATENCYTOP
 	int				latency_record_count;
 	struct latency_record		latency_record[LT_SAVECOUNT];

kernel/fork.c +1 -0

index d75a528f7b21..d34c9c00baea 100644
@@ -2246,6 +2246,7 @@ static __latent_entropy struct task_struct *copy_process(
 	p->nr_dirtied = 0;
 	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
 	p->dirty_paused_when = 0;
+	p->bdp_nr_dirtied_pause = -1;
 
 	p->pdeath_signal = 0;
 	INIT_LIST_HEAD(&p->thread_group);

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #29 lore raw

PATCH 12/14 mm: support write throttling for async buffered writes

In reply to Stefan Roesch

This change adds support for async write throttling in the function balance_dirty_pages(). So far if throttling was required, the code was waiting synchronously as long as the writes were throttled. This change introduces asynchronous throttling. Instead of waiting in the function balance_dirty_pages(), the timeout is set in the task_struct field bdp_pause. Once the timeout has expired, the writes are no longer throttled.

- Add a new parameter to the balance_dirty_pages() function
- This allows the caller to pass in the nowait flag
- When the nowait flag is specified, the code does not wait in balance_dirty_pages(), but instead stores the wait expiration in the new task_struct field bdp_pause.

- The function balance_dirty_pages_ratelimited() resets the new values in the task_struct, once the timeout has expired

This change is required to support write throttling for the async buffered writes. While the writes are throttled, io_uring still can make progress with processing other requests.

Signed-off-by Stefan Roesch <[email protected]>

---
 include/linux/writeback.h |  1 +
 mm/filemap.c              |  2 +-
 mm/page-writeback.c       | 54 ++++++++++++++++++++++++++++-----------
 3 files changed, 41 insertions(+), 16 deletions(-)

include/linux/writeback.h +1 -0

index fec248ab1fec..48176a8047db 100644
@@ -373,6 +373,7 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
 
 void wb_update_bandwidth(struct bdi_writeback *wb);
 void balance_dirty_pages_ratelimited(struct address_space *mapping);
+void  balance_dirty_pages_ratelimited_flags(struct address_space *mapping, bool is_async);
 bool wb_over_bg_thresh(struct bdi_writeback *wb);
 
 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,

mm/filemap.c +1 -1

index 19065ad95a4c..aa51ff1a0e8f 100644
@@ -3805,7 +3805,7 @@ static ssize_t do_generic_perform_write(struct file *file, struct iov_iter *i,
 		pos += status;
 		written += status;
 
-		balance_dirty_pages_ratelimited(mapping);
+		balance_dirty_pages_ratelimited_flags(mapping, flags & AOP_FLAGS_NOWAIT);
 	} while (iov_iter_count(i));
 
 	return written ? written : status;

mm/page-writeback.c +39 ~~-15~~

93 lines not on this page · raw message

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #30 lore raw

PATCH 13/14 io_uring: support write throttling for async buffered writes

In reply to Stefan Roesch

This adds the process-level throttling for the block layer for async buffered writes to io-uring.In io_write the code now checks if the write needs to be throttled. If this is required, it adds the request to the list of pending io requests and starts a timer. After the timer expires, it submits the list of pending writes.

- Add new list called pending_ios for delayed writes (throttled writes) to struct io_uring_task. The list is protected by the task_lock spin lock.
- Add new timer to struct io_uring_task.

Signed-off-by Stefan Roesch <[email protected]>

---
 fs/io_uring.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 91 insertions(+), 7 deletions(-)

fs/io_uring.c +91 -7

index 507f28b5b2bb..7bb77700ffac 100644
@@ -461,6 +461,11 @@ struct io_ring_ctx {
 	};
 };
 
+struct pending_list {
+	struct list_head list;
+	struct io_kiocb *req;
+};
+
 struct io_uring_task {
 	/* submission side */
 	int			cached_refs;

@@ -477,6 +482,9 @@ struct io_uring_task {
 	struct io_wq_work_list	prior_task_list;
 	struct callback_head	task_work;
 	bool			task_running;
+
+	struct pending_list	pending_ios;
+	struct timer_list	timer;
 };
 
 /*

@@ -1134,13 +1142,14 @@ static void io_rsrc_put_work(struct work_struct *work);
 
 static void io_req_task_queue(struct io_kiocb *req);
 static void __io_submit_flush_completions(struct io_ring_ctx *ctx);
-static int io_req_prep_async(struct io_kiocb *req);
+static int io_req_prep_async(struct io_kiocb *req, bool force);
 
 static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 				 unsigned int issue_flags, u32 slot_index);
 static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
 
 static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
+static void delayed_write_fn(struct timer_list *tmr);
 
 static struct kmem_cache *req_cachep;

@@ -2462,6 +2471,31 @@ static void io_req_task_queue_reissue(struct io_kiocb *req)
 	io_req_task_work_add(req, false);
 }
 
+static int io_req_task_queue_reissue_delayed(struct io_kiocb *req)
+{
+	struct io_uring_task *tctx = req->task->io_uring;
+	struct pending_list *pending = kmalloc(sizeof(struct pending_list), GFP_KERNEL);
+	bool empty;
+
+	if (!pending)
+		return -ENOMEM;
+	pending->req = req;
+
+	spin_lock_irq(&tctx->task_lock);
+	empty = list_empty(&tctx->pending_ios.list);
+	list_add_tail(&pending->list, &tctx->pending_ios.list);
+
+	if (empty) {
+		timer_setup(&tctx->timer, delayed_write_fn, 0);
+
+		tctx->timer.expires = current->bdp_pause;
+		add_timer(&tctx->timer);
+	}
+	spin_unlock_irq(&tctx->task_lock);
+
+	return 0;
+}
+
 static inline void io_queue_next(struct io_kiocb *req)
 {
 	struct io_kiocb *nxt = io_req_find_next(req);

@@ -2770,7 +2804,7 @@ static bool io_resubmit_prep(struct io_kiocb *req)
 	struct io_async_rw *rw = req->async_data;
 
 	if (!req_has_async_data(req))
-		return !io_req_prep_async(req);
+		return !io_req_prep_async(req, false);
 	iov_iter_restore(&rw->s.iter, &rw->s.iter_state);
 	return true;
 }

@@ -3751,6 +3785,38 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return io_prep_rw(req, sqe);
 }
 
+static inline unsigned long write_delay(void)
+{
+	if (likely(current->bdp_nr_dirtied_pause == -1 ||
+			!time_before(jiffies, current->bdp_pause)))
+		return 0;
+
+	return current->bdp_pause;
+}
+
+static void delayed_write_fn(struct timer_list *tmr)
+{
+	struct io_uring_task *tctx = from_timer(tctx, tmr, timer);
+	struct list_head *curr;
+	struct list_head *next;
+	LIST_HEAD(pending_ios);
+
+	/* Move list to temporary list. */
+	spin_lock_irq(&tctx->task_lock);
+	list_splice_init(&tctx->pending_ios.list, &pending_ios);
+	spin_unlock_irq(&tctx->task_lock);
+
+	list_for_each_safe(curr, next, &pending_ios) {
+		struct pending_list *io;
+
+		io = list_entry(curr, struct pending_list, list);
+		io_req_task_queue_reissue(io->req);
+
+		list_del(curr);
+		kfree(io);
+	}
+}
+
 static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_rw_state __s, *s = &__s;

@@ -3759,6 +3825,18 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
 	ssize_t ret, ret2;
 
+	/* Write throttling active? */
+	if (unlikely(write_delay()) && !(kiocb->ki_flags & IOCB_DIRECT)) {
+		int ret = io_req_prep_async(req, true);
+
+		if (unlikely(ret))
+			io_req_complete_failed(req, ret);
+		else
+			ret = io_req_task_queue_reissue_delayed(req);
+
+		return ret;
+	}
+
 	if (!req_has_async_data(req)) {
 		ret = io_import_iovec(WRITE, req, &iovec, s, issue_flags);
 		if (unlikely(ret < 0))

@@ -6597,9 +6675,9 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return -EINVAL;
 }
 
-static int io_req_prep_async(struct io_kiocb *req)
+static int io_req_prep_async(struct io_kiocb *req, bool force)
 {
-	if (!io_op_defs[req->opcode].needs_async_setup)
+	if (!force && !io_op_defs[req->opcode].needs_async_setup)
 		return 0;
 	if (WARN_ON_ONCE(req_has_async_data(req)))
 		return -EFAULT;

@@ -6609,6 +6687,10 @@ static int io_req_prep_async(struct io_kiocb *req)
 	switch (req->opcode) {
 	case IORING_OP_READV:
 		return io_rw_prep_async(req, READ);
+	case IORING_OP_WRITE:
+		if (!force)
+			break;
+		fallthrough;
 	case IORING_OP_WRITEV:
 		return io_rw_prep_async(req, WRITE);
 	case IORING_OP_SENDMSG:

@@ -6618,6 +6700,7 @@ static int io_req_prep_async(struct io_kiocb *req)
 	case IORING_OP_CONNECT:
 		return io_connect_prep_async(req);
 	}
+
 	printk_once(KERN_WARNING "io_uring: prep_async() bad opcode %d\n",
 		    req->opcode);
 	return -EFAULT;

@@ -6651,7 +6734,7 @@ static __cold void io_drain_req(struct io_kiocb *req)
 	}
 	spin_unlock(&ctx->completion_lock);
 
-	ret = io_req_prep_async(req);
+	ret = io_req_prep_async(req, false);
 	if (ret) {
 fail:
 		io_req_complete_failed(req, ret);

@@ -7146,7 +7229,7 @@ static void io_queue_sqe_fallback(struct io_kiocb *req)
 	} else if (unlikely(req->ctx->drain_active)) {
 		io_drain_req(req);
 	} else {
-		int ret = io_req_prep_async(req);
+		int ret = io_req_prep_async(req, false);
 
 		if (unlikely(ret))
 			io_req_complete_failed(req, ret);

@@ -7345,7 +7428,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		struct io_kiocb *head = link->head;
 
 		if (!(req->flags & REQ_F_FAIL)) {
-			ret = io_req_prep_async(req);
+			ret = io_req_prep_async(req, false);
 			if (unlikely(ret)) {
 				req_fail_link_node(req, ret);
 				if (!(head->flags & REQ_F_FAIL))

@@ -8785,6 +8868,7 @@ static __cold int io_uring_alloc_task_context(struct task_struct *task,
 	INIT_WQ_LIST(&tctx->task_list);
 	INIT_WQ_LIST(&tctx->prior_task_list);
 	init_task_work(&tctx->task_work, tctx_task_work);
+	INIT_LIST_HEAD(&tctx->pending_ios.list);
 	return 0;
 }

Signature · 1 line

2.30.2

Stefan Roesch

author

2022-02-14 17:44 UTC #31 lore raw

PATCH 14/14 block: enable async buffered writes for block devices.

In reply to Stefan Roesch

This introduces the flag FMODE_BUF_WASYNC. If devices support async buffered writes, this flag can be set. It also enables async buffered writes for block devices.

Signed-off-by Stefan Roesch <[email protected]>

---
 block/fops.c       | 5 +----
 fs/read_write.c    | 3 ++-
 include/linux/fs.h | 3 +++
 3 files changed, 6 insertions(+), 5 deletions(-)

block/fops.c +1 -4

index 4f59e0f5bf30..75b36f8b5e71 100644
@@ -489,7 +489,7 @@ static int blkdev_open(struct inode *inode, struct file *filp)
 	 * during an unstable branch.
 	 */
 	filp->f_flags |= O_LARGEFILE;
-	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC;
+	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC | FMODE_BUF_WASYNC;
 
 	if (filp->f_flags & O_NDELAY)
 		filp->f_mode |= FMODE_NDELAY;

@@ -544,9 +544,6 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (iocb->ki_pos >= size)
 		return -ENOSPC;
 
-	if ((iocb->ki_flags & (IOCB_NOWAIT | IOCB_DIRECT)) == IOCB_NOWAIT)
-		return -EOPNOTSUPP;
-
 	size -= iocb->ki_pos;
 	if (iov_iter_count(from) > size) {
 		shorted = iov_iter_count(from) - size;

fs/read_write.c +2 -1

index 0074afa7ecb3..58233844a9d8 100644
@@ -1641,7 +1641,8 @@ ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	if (iocb->ki_flags & IOCB_APPEND)
 		iocb->ki_pos = i_size_read(inode);
 
-	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+	if ((iocb->ki_flags & IOCB_NOWAIT) &&
+		(!(iocb->ki_flags & IOCB_DIRECT) && !(file->f_mode & FMODE_BUF_WASYNC)))
 		return -EINVAL;
 
 	count = iov_iter_count(from);

include/linux/fs.h +3 -0

index e62dba6ed453..a19c7903e031 100644
@@ -176,6 +176,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File supports async buffered reads */
 #define FMODE_BUF_RASYNC	((__force fmode_t)0x40000000)
 
+/* File supports async nowait buffered writes */
+#define FMODE_BUF_WASYNC	((__force fmode_t)0x80000000)
+
 /*
  * Attribute flags.  These should be or-ed together to figure out what
  * has been changed!

Signature · 1 line

2.30.2

Hao Xu

2022-02-15 03:59 UTC #32 lore raw

In reply to Stefan Roesch

Quoted 144 lines · Stefan Roesch

This patch series adds support for async buffered writes. Currently io-uring only supports buffered writes in the slow path, by processing them in the io workers. With this patch series it is now possible to support buffered writes in the fast path. To be able to use the fast path the required pages must be in the page cache or they can be loaded with noio. Otherwise they still get punted to the slow path.
If a buffered write request requires more than one page, it is possible that only part of the request can use the fast path, the resst will be completed by the io workers.
Support for async buffered writes:
Patch 1: fs: Add flags parameter to __block_write_begin_int
Add a flag parameter to the function __block_write_begin_int to allow specifying a nowait parameter.
Patch 2: mm: Introduce do_generic_perform_write
Introduce a new do_generic_perform_write function. The function is split off from the existing generic_perform_write() function. It allows to specify an additional flag parameter. This parameter is used to specify the nowait flag.
Patch 3: mm: add noio support in filemap_get_pages
This allows to allocate pages with noio, if a page for async buffered writes is not yet loaded in the page cache.
Patch 4: mm: Add support for async buffered writes
For async buffered writes allocate pages without blocking on the allocation.
Patch 5: fs: split off __alloc_page_buffers function
Split off __alloc_page_buffers() function with new gfp_t parameter.
Patch 6: fs: split off __create_empty_buffers function
Split off __create_empty_buffers() function with new gfp_t parameter.
Patch 7: fs: Add aop_flags parameter to create_page_buffers()
Add aop_flags to create_page_buffers() function. Use atomic allocation for async buffered writes.
Patch 8: fs: add support for async buffered writes
Return -EAGAIN instead of -ENOMEM for async buffered writes. This will cause the write request to be processed by an io worker.
Patch 9: io_uring: add support for async buffered writes
This enables the async buffered writes for block devices in io_uring. Buffered writes are enabled for blocks that are already in the page cache or can be acquired with noio.
Patch 10: io_uring: Add tracepoint for short writes
Support for write throttling of async buffered writes:
Patch 11: sched: add new fields to task_struct
Add two new fields to the task_struct. These fields store the deadline after which writes are no longer throttled.
Patch 12: mm: support write throttling for async buffered writes
This changes the balance_dirty_pages function to take an additonal parameter. When nowait is specified the write throttling code no longer waits synchronously for the deadline to expire. Instead it sets the fields in task_struct. Once the deadline expires the fields are reset.
Patch 13: io_uring: support write throttling for async buffered writes
Adds support to io_uring for write throttling. When the writes are throttled, the write requests are added to the pending io list. Once the write throttling deadline expires, the writes are submitted.
Enable async buffered write support
Patch 14: fs: add flag to support async buffered writes
This sets the flags that enables async buffered writes for block devices.
Testing:
This patch has been tested with xfstests and fio.
Peformance results:
For fio the following results have been obtained with a queue depth of 1 and 4k block size (runtime 600 secs):
sequential writes:
without patch with patch
throughput: 329 Mib/s 1032Mib/s
iops: 82k 264k
slat (nsec) 2332 3340
clat (nsec) 9017 60
CPU util%: 37% 78%
random writes:
without patch with patch
throughput: 307 Mib/s 909Mib/s
iops: 76k 227k
slat (nsec) 2419 3780
clat (nsec) 9934 59
CPU util%: 57% 88%
For an io depth of 1, the new patch improves throughput by close to 3 times and also the latency is considerably reduced. To achieve the same or better performance with the exisiting code an io depth of 4 is required.
Especially for mixed workloads this is a considerable improvement.
Stefan Roesch (14):
fs: Add flags parameter to __block_write_begin_int
mm: Introduce do_generic_perform_write
mm: add noio support in filemap_get_pages
mm: Add support for async buffered writes
fs: split off __alloc_page_buffers function
fs: split off __create_empty_buffers function
fs: Add aop_flags parameter to create_page_buffers()
fs: add support for async buffered writes
io_uring: add support for async buffered writes
io_uring: Add tracepoint for short writes
sched: add new fields to task_struct
mm: support write throttling for async buffered writes
io_uring: support write throttling for async buffered writes
block: enable async buffered writes for block devices.
  block/fops.c                    |   5 +-
  fs/buffer.c                     | 103 ++++++++++++++++---------
  fs/internal.h                   |   3 +-
  fs/io_uring.c                   | 130 +++++++++++++++++++++++++++++---
  fs/iomap/buffered-io.c          |   4 +-
  fs/read_write.c                 |   3 +-
  include/linux/fs.h              |   4 +
  include/linux/sched.h           |   3 +
  include/linux/writeback.h       |   1 +
  include/trace/events/io_uring.h |  25 ++++++
  kernel/fork.c                   |   1 +
  mm/filemap.c                    |  34 +++++++--
  mm/folio-compat.c               |   4 +
  mm/page-writeback.c             |  54 +++++++++----
  14 files changed, 298 insertions(+), 76 deletions(-)

Quoted 2 lines

base-commit: f1baf68e1383f6ed93eb9cff2866d46562607a43

It's a little bit different between buffered read and buffered write, there may be block points in detail filesystems due to journal operations for the latter.

Stefan Roesch

author

2022-02-15 17:38 UTC #33 lore raw

Quoted 139 lines · Hao Xu

Quoted 138 lines · Stefan Roesch
This patch series adds support for async buffered writes. Currently io-uring only supports buffered writes in the slow path, by processing them in the io workers. With this patch series it is now possible to support buffered writes in the fast path. To be able to use the fast path the required pages must be in the page cache or they can be loaded with noio. Otherwise they still get punted to the slow path.
If a buffered write request requires more than one page, it is possible that only part of the request can use the fast path, the resst will be completed by the io workers.
Support for async buffered writes:
   Patch 1: fs: Add flags parameter to __block_write_begin_int Add a flag parameter to the function __block_write_begin_int to allow specifying a nowait parameter.
        Patch 2: mm: Introduce do_generic_perform_write Introduce a new do_generic_perform_write function. The function is split off from the existing generic_perform_write() function. It allows to specify an additional flag parameter. This parameter is used to specify the nowait flag.
        Patch 3: mm: add noio support in filemap_get_pages This allows to allocate pages with noio, if a page for async buffered writes is not yet loaded in the page cache. Patch 4: mm: Add support for async buffered writes For async buffered writes allocate pages without blocking on the allocation.
   Patch 5: fs: split off __alloc_page_buffers function Split off __alloc_page_buffers() function with new gfp_t parameter.
   Patch 6: fs: split off __create_empty_buffers function Split off __create_empty_buffers() function with new gfp_t parameter.
   Patch 7: fs: Add aop_flags parameter to create_page_buffers() Add aop_flags to create_page_buffers() function. Use atomic allocation for async buffered writes.
   Patch 8: fs: add support for async buffered writes Return -EAGAIN instead of -ENOMEM for async buffered writes. This will cause the write request to be processed by an io worker.
   Patch 9: io_uring: add support for async buffered writes This enables the async buffered writes for block devices in io_uring. Buffered writes are enabled for blocks that are already in the page cache or can be acquired with noio.
   Patch 10: io_uring: Add tracepoint for short writes
Support for write throttling of async buffered writes:
   Patch 11: sched: add new fields to task_struct
     Add two new fields to the task_struct. These fields store the deadline after which writes are no longer throttled.
   Patch 12: mm: support write throttling for async buffered writes This changes the balance_dirty_pages function to take an additonal parameter. When nowait is specified the write throttling code no longer waits synchronously for the deadline to expire. Instead it sets the fields in task_struct. Once the deadline expires the fields are reset.
        Patch 13: io_uring: support write throttling for async buffered writes Adds support to io_uring for write throttling. When the writes are throttled, the write requests are added to the pending io list. Once the write throttling deadline expires, the writes are submitted. Enable async buffered write support
   Patch 14: fs: add flag to support async buffered writes
     This sets the flags that enables async buffered writes for block devices.
Testing:
   This patch has been tested with xfstests and fio.
Peformance results:
   For fio the following results have been obtained with a queue depth of 1 and 4k block size (runtime 600 secs):
                  sequential writes:
                  without patch                 with patch throughput:       329 Mib/s                    1032Mib/s iops:              82k                          264k
   slat (nsec)      2332                          3340
   clat (nsec)      9017                            60
                       CPU util%:         37%                          78%
                  random writes:
                  without patch                 with patch throughput:       307 Mib/s                    909Mib/s iops:              76k                         227k slat (nsec)      2419                         3780 clat (nsec)      9934                           59
   CPU util%:         57%                          88%
For an io depth of 1, the new patch improves throughput by close to 3 times and also the latency is considerably reduced. To achieve the same or better performance with the exisiting code an io depth of 4 is required.
Especially for mixed workloads this is a considerable improvement.
Stefan Roesch (14):
   fs: Add flags parameter to __block_write_begin_int
   mm: Introduce do_generic_perform_write
   mm: add noio support in filemap_get_pages
   mm: Add support for async buffered writes
   fs: split off __alloc_page_buffers function
   fs: split off __create_empty_buffers function
   fs: Add aop_flags parameter to create_page_buffers()
   fs: add support for async buffered writes
   io_uring: add support for async buffered writes
   io_uring: Add tracepoint for short writes
   sched: add new fields to task_struct
   mm: support write throttling for async buffered writes
   io_uring: support write throttling for async buffered writes
   block: enable async buffered writes for block devices.
block/fops.c                    |   5 +-
fs/buffer.c                     | 103 ++++++++++++++++--------- fs/internal.h                   |   3 +-
fs/io_uring.c                   | 130 +++++++++++++++++++++++++++++--- fs/iomap/buffered-io.c          |   4 +-
fs/read_write.c                 |   3 +- include/linux/fs.h              |   4 + include/linux/sched.h           |   3 + include/linux/writeback.h       |   1 + include/trace/events/io_uring.h | 25 ++++++
kernel/fork.c                   |   1 +
mm/filemap.c                    | 34 +++++++-- mm/folio-compat.c               |   4 + mm/page-writeback.c             | 54 +++++++++----
  14 files changed, 298 insertions(+), 76 deletions(-)

Quoted 6 lines

Quoted 2 lines
base-commit: f1baf68e1383f6ed93eb9cff2866d46562607a43
It's a little bit different between buffered read and buffered write, there may be block points in detail filesystems due to journal operations for the latter.

This patch series only adds support for async buffered writes for block devices, not filesystems.