ext2: allocate ->s_blockgroup_lock separately

As spotted by kmemtrace, struct ext2_sb_info is 17024 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 ext2_sb_info
enough to fit a 1 KB slab cache so now we allocate 16 KB + 1 KB instead of
32 KB saving 15 KB of memory.

Acked-by: Andreas Dilger <adilger@sun.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/ext2_fs_sb.h b/include/linux/ext2_fs_sb.h
index dc541f3653d1..1cdb66367c98 100644
--- a/include/linux/ext2_fs_sb.h
+++ b/include/linux/ext2_fs_sb.h
@@ -101,7 +101,7 @@ struct ext2_sb_info {
         struct percpu_counter s_freeblocks_counter;
         struct percpu_counter s_freeinodes_counter;
         struct percpu_counter s_dirs_counter;
-        struct blockgroup_lock s_blockgroup_lock;
+        struct blockgroup_lock *s_blockgroup_lock;
         /* root of the per fs reservation window tree */
         spinlock_t s_rsv_window_lock;
         struct rb_root s_rsv_window_root;
@@ -111,7 +111,7 @@ struct ext2_sb_info {
 static inline spinlock_t *
 sb_bgl_lock(struct ext2_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  /* _LINUX_EXT2_FS_SB */