f2fs: merge two uchar variable in struct node_info to reduce memory cost

This patch moves one member of struct nat_entry: _flag_ to struct node_info, so _version_ in struct node_info and _flag_ with unsigned char type will merge to one 32-bit space in register/memory. Then the size of nat_entry will reduce its size from 28 bytes to 24 bytes and slab memory using by f2fs will be reduced.

changes from v1:
o introduce inline copy_node_info() to copy valid data from node info suggested by Jaegeuk Kim, it can avoid bug.

Signed-off-by Chao Yu <[email protected]>

---
 fs/f2fs/node.c |  4 ++--
 fs/f2fs/node.h | 33 ++++++++++++++++++++++-----------
 2 files changed, 24 insertions(+), 13 deletions(-)

fs/f2fs/node.c +2 -2

index f83326c..5aa54a0 100644
@@ -268,7 +268,7 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
        e = __lookup_nat_cache(nm_i, ni->nid);
        if (!e) {
                e = grab_nat_entry(nm_i, ni->nid);
-               e->ni = *ni;
+               copy_node_info(&e->ni, ni);
                f2fs_bug_on(sbi, ni->blk_addr == NEW_ADDR);
        } else if (new_blkaddr == NEW_ADDR) {
                /*

@@ -276,7 +276,7 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
                 * previous nat entry can be remained in nat cache.
                 * So, reinitialize it with new information.
                 */
-               e->ni = *ni;
+               copy_node_info(&e->ni, ni);
                f2fs_bug_on(sbi, ni->blk_addr != NULL_ADDR);
        }
 

fs/f2fs/node.h +22 -12

index d10b644..eb59167 100644
@@ -29,6 +29,14 @@
 /* return value for read_node_page */
 #define LOCKED_PAGE    1
 
+/* For flag in struct node_info */
+enum {
+       IS_CHECKPOINTED,        /* is it checkpointed before? */
+       HAS_FSYNCED_INODE,      /* is the inode fsynced before? */
+       HAS_LAST_FSYNC,         /* has the latest node fsync mark? */
+       IS_DIRTY,               /* this nat entry is dirty? */
+};
+
 /*
  * For node information
  */

@@ -37,18 +45,11 @@ struct node_info {
        nid_t ino;              /* inode number of the node's owner */
        block_t blk_addr;       /* block address of the node */
        unsigned char version;  /* version of the node */
-};
-
-enum {
-       IS_CHECKPOINTED,        /* is it checkpointed before? */
-       HAS_FSYNCED_INODE,      /* is the inode fsynced before? */
-       HAS_LAST_FSYNC,         /* has the latest node fsync mark? */
-       IS_DIRTY,               /* this nat entry is dirty? */
+       unsigned char flag;     /* for node information bits */
 };
 
 struct nat_entry {
        struct list_head list;  /* for clean or dirty nat list */
-       unsigned char flag;     /* for node information bits */
        struct node_info ni;    /* in-memory node information */
 };
 

@@ -63,20 +64,30 @@ struct nat_entry {
 
 #define inc_node_version(version)      (++version)
 
+static inline void copy_node_info(struct node_info *dst,
+                                               struct node_info *src)
+{
+       dst->nid = src->nid;
+       dst->ino = src->ino;
+       dst->blk_addr = src->blk_addr;
+       dst->version = src->version;
+       /* should not copy flag here */
+}
+
 static inline void set_nat_flag(struct nat_entry *ne,
                                unsigned int type, bool set)
 {
        unsigned char mask = 0x01 << type;
        if (set)
-               ne->flag |= mask;
+               ne->ni.flag |= mask;
        else
-               ne->flag &= ~mask;
+               ne->ni.flag &= ~mask;
 }
 
 static inline bool get_nat_flag(struct nat_entry *ne, unsigned int type)
 {
        unsigned char mask = 0x01 << type;
-       return ne->flag & mask;
+       return ne->ni.flag & mask;
 }
 
 static inline void nat_reset_flag(struct nat_entry *ne)
--

2.1.2

------------------------------------------------------------------------------
Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE
http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
_______________________________________________
Linux-f2fs-devel mailing list [email protected]
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

-----Original Message-----
From: Changman Lee [mailto:[email protected]]
Sent: Wednesday, December 17, 2014 11:09 PM
To: Chao Yu
Cc: Jaegeuk Kim; Changman Lee; [email protected]; [email protected]; [email protected]
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: merge two uchar variable in struct node_info to reduce memory cost

Hi Yu,

This patch is effective only in 32 bit machine. In case of 64 bit machine, nat_entry will be aligned in 8 bytes due to pointer variable (i.e. struct list_head). So it can't get any benefit to reduce memory usage. In the case of node_info, however, it will be gain in terms of memory usage.
Hence, I think it's not correct for commit log to describe this patch.

Thanks,

Reviewed-by Changman Lee <[email protected]>

Hi Changman,

Quoted 9 lines

-----Original Message-----
From: Changman Lee [mailto:[email protected]]
Sent: Wednesday, December 17, 2014 11:09 PM
To: Chao Yu
Cc: Jaegeuk Kim; Changman Lee; [email protected]; [email protected]; [email protected]
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: merge two uchar variable in struct node_info to reduce memory cost

Quoted 9 lines

Hi Yu,

This patch is effective only in 32 bit machine. In case of 64 bit machine, nat_entry will be aligned in 8 bytes due to pointer variable (i.e. struct list_head). So it can't get any benefit to reduce memory usage. In the case of node_info, however, it will be gain in terms of memory usage.
Hence, I think it's not correct for commit log to describe this patch.

Thanks for your review! :)

AFFIK, in 64 bit machine, size of struct nat_entry is 40 bytes before this patch apply, the reason is that our compiler will fill 3 bytes pads after flag as nid's offset should align to type size of nid, and then fill 7 byte pads after version as size of structure should align to 64 bits when the struct size is bigger than 64 bits.
layout of struct nat_entry:

|-----8 bytes-----|
|list.next        |
|list.prev        |
|flag    |nid     |
|ino     |blk_addr|
|version          |

After we apply this patch, size of struct nat_entry will be reduced to 32 bytes. Please correct me if I'm wrong.

Anyway, I agreed that commit log should be uptodate.

Thanks,
Yu

Quoted 4 lines

Thanks,

Reviewed-by Changman Lee <[email protected]>