ext4: allocate ->s_blockgroup_lock separately

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.

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: "Theodore Ts'o" <tytso@mit.edu>

2 files changed, 11 insertions, 3 deletions

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index e318f486cc24..4e4d9cc3f40d 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -62,7 +62,7 @@ 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;
 
         /* Journaling */
@@ -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 f7371a6a923d..a3768709ce05 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -615,6 +615,7 @@ 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;
 }
@@ -2021,6 +2022,13 @@ 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;
@@ -2332,7 +2340,7 @@ 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);