ext3: speed up group trim with the right free block count.

When we trim some free blocks in a group of ext3, we should
calculate the free blocks properly and check whether there are
enough freed blocks left for us to trim. Current solution will
only calculate free spaces if they are large for a trim which
is wrong.

Let us see a small example:
a group has 1.5M free which are 300k, 300k, 300k, 300k, 300k.
And minblocks is 1M. With current solution, we have to iterate
the whole group since these 300k will never be subtracted from
1.5M. But actually we should exit after we find the first 2
free spaces since the left 3 chunks only sum up to 900K if we
subtract the first 600K although they can't be trimed.

Cc: Jan Kara <jack@suse.cz>
Cc: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
index 5b8344fab79d5f9ec4794faa95b24a9b76ac6639..db1906b4e39cff78ac59d9326e96605b0ab73025 100644 (file)
--- a/fs/ext3/balloc.c
+++ b/fs/ext3/balloc.c
@@ -1991,6 +1991,7 @@ ext3_grpblk_t ext3_trim_all_free(struct super_block *sb, unsigned int group,
                spin_unlock(sb_bgl_lock(sbi, group));
                percpu_counter_sub(&sbi->s_freeblocks_counter, next - start);
 
+               free_blocks -= next - start;
                /* Do not issue a TRIM on extents smaller than minblocks */
                if ((next - start) < minblocks)
                        goto free_extent;
@@ -2040,7 +2041,7 @@ free_extent:
                cond_resched();
 
                /* No more suitable extents */
-               if ((free_blocks - count) < minblocks)
+               if (free_blocks < minblocks)
                        break;
        }