ext3: allocate ->s_blockgroup_lock separately

As spotted by kmemtrace, struct ext3_sb_info is 17152 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 ext3_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>

2 files changed, 11 insertions, 3 deletions

diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index c22d01467bd1..01c235bc2054 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -439,6 +439,7 @@ static void ext3_put_super (struct super_block * sb)
                 ext3_blkdev_remove(sbi);
         }
         sb->s_fs_info = NULL;
+        kfree(sbi->s_blockgroup_lock);
         kfree(sbi);
         return;
 }
@@ -1546,6 +1547,13 @@ static int ext3_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 = EXT3_DEF_RESUID;
@@ -1786,7 +1794,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
                 goto failed_mount;
         }
 
-        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, logic_sb_block, i);
diff --git a/include/linux/ext3_fs_sb.h b/include/linux/ext3_fs_sb.h
index e024e38248ff..76fdc0f4b028 100644
--- a/include/linux/ext3_fs_sb.h
+++ b/include/linux/ext3_fs_sb.h
@@ -60,7 +60,7 @@ struct ext3_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;
@@ -86,7 +86,7 @@ struct ext3_sb_info {
 static inline spinlock_t *
 sb_bgl_lock(struct ext3_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_EXT3_FS_SB */