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Subject[PATCH 4/4] ext4: allocate ->s_blockgroup_lock separately
From: Pekka Enberg <penberg@cs.helsinki.fi>

As spotted by kmemtrace, struct ext4_sb_info is 17664 bytes on 64-bit which
makes it a very bad fit for SLAB allocators. The culprit of the wasted memory
is ->s_blockgroup_lock which can be as big as 16 KB when NR_CPUS >= 32.

To fix that, allocate ->s_blockgroup_lock, which fits nicely in a order 2 page
in the worst case, separately. This shinks down struct ext4_sb_info enough to
fit a 2 KB slab cache so now we allocate 16 KB + 2 KB instead of 32 KB saving
14 KB of memory.

Cc: Andreas Dilger <adilger@sun.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---
fs/ext4/ext4_sb.h | 4 ++--
fs/ext4/super.c | 10 +++++++++-
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index b21f167..ed3bc9c 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -61,7 +61,7 @@ struct ext4_sb_info {
struct percpu_counter s_freeinodes_counter;
struct percpu_counter s_dirs_counter;
struct percpu_counter s_dirtyblocks_counter;
- struct blockgroup_lock s_blockgroup_lock;
+ struct blockgroup_lock *s_blockgroup_lock;
struct proc_dir_entry *s_proc;

/* root of the per fs reservation window tree */
@@ -149,7 +149,7 @@ struct ext4_sb_info {
static inline spinlock_t *
sb_bgl_lock(struct ext4_sb_info *sbi, unsigned int block_group)
{
- return bgl_lock_ptr(&sbi->s_blockgroup_lock, block_group);
+ return bgl_lock_ptr(sbi->s_blockgroup_lock, block_group);
}

#endif /* _EXT4_SB */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e4a241c..1add517 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -497,6 +497,7 @@ static void ext4_put_super(struct super_block *sb)
ext4_blkdev_remove(sbi);
}
sb->s_fs_info = NULL;
+ kfree(sbi->s_blockgroup_lock);
kfree(sbi);
return;
}
@@ -1883,6 +1884,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
if (!sbi)
return -ENOMEM;
+
+ sbi->s_blockgroup_lock =
+ kzalloc(sizeof(struct blockgroup_lock), GFP_KERNEL);
+ if (!sbi->s_blockgroup_lock) {
+ kfree(sbi);
+ return -ENOMEM;
+ }
sb->s_fs_info = sbi;
sbi->s_mount_opt = 0;
sbi->s_resuid = EXT4_DEF_RESUID;
@@ -2179,7 +2187,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
&sbi->s_inode_readahead_blks);
#endif

- bgl_lock_init(&sbi->s_blockgroup_lock);
+ bgl_lock_init(sbi->s_blockgroup_lock);

for (i = 0; i < db_count; i++) {
block = descriptor_loc(sb, logical_sb_block, i);
--
1.5.4.3


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