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>

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 647cd88..da8bdea 100644 (file)
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -132,6 +132,7 @@ static void ext2_put_super (struct super_block * sb)
        percpu_counter_destroy(&sbi->s_dirs_counter);
        brelse (sbi->s_sbh);
        sb->s_fs_info = NULL;
+       kfree(sbi->s_blockgroup_lock);
        kfree(sbi);
 
        return;
@@ -756,6 +757,13 @@ static int ext2_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_sb_block = sb_block;
 
@@ -983,7 +991,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
                printk ("EXT2-fs: not enough memory\n");
                goto failed_mount;
        }
-       bgl_lock_init(&sbi->s_blockgroup_lock);
+       bgl_lock_init(sbi->s_blockgroup_lock);
        sbi->s_debts = kcalloc(sbi->s_groups_count, sizeof(*sbi->s_debts), GFP_KERNEL);
        if (!sbi->s_debts) {
                printk ("EXT2-fs: not enough memory\n");

diff --git a/include/linux/ext2_fs_sb.h b/include/linux/ext2_fs_sb.h
index dc541f3..1cdb663 100644 (file)
--- 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 */