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

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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>
This commit is contained in:
Tao Ma 2011-01-21 22:09:20 +08:00 committed by Jan Kara
parent 4b44dd300d
commit bbac751dc8
1 changed files with 2 additions and 1 deletions
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3
fs/ext3/balloc.c
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@ -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)); spin_unlock(sb_bgl_lock(sbi, group));
percpu_counter_sub(&sbi->s_freeblocks_counter, next - start); percpu_counter_sub(&sbi->s_freeblocks_counter, next - start);
free_blocks -= next - start;
/* Do not issue a TRIM on extents smaller than minblocks */ /* Do not issue a TRIM on extents smaller than minblocks */
if ((next - start) < minblocks) if ((next - start) < minblocks)
goto free_extent; goto free_extent;
@ -2040,7 +2041,7 @@ ext3_grpblk_t ext3_trim_all_free(struct super_block *sb, unsigned int group,
cond_resched(); cond_resched();
/* No more suitable extents */ /* No more suitable extents */
if ((free_blocks - count) < minblocks) if (free_blocks < minblocks)
break; break;
} }