On Fri, 21 Jan 2011, Tao Ma wrote:
> From: Tao Ma <boyu.mt@xxxxxxxxxx>
>
> 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@xxxxxxx>
> Cc: Lukas Czerner <lczerner@xxxxxxxxxx>
> Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
> ---
> fs/ext3/balloc.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
> index 045995c..971e1bd 100644
> --- a/fs/ext3/balloc.c
> +++ b/fs/ext3/balloc.c
> @@ -1922,7 +1922,7 @@ ext3_grpblk_t ext3_trim_all_free(struct super_block *sb, unsigned int group,
> ext3_grpblk_t minblocks)
> {
> handle_t *handle;
> - ext3_grpblk_t next, free_blocks, bit, freed, count = 0;
> + ext3_grpblk_t next, free_blocks, bit, freed, count = 0, free_count = 0;
> ext3_fsblk_t discard_block;
> struct ext3_sb_info *sbi;
> struct buffer_head *gdp_bh, *bitmap_bh = NULL;
> @@ -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_count += 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 - free_count) < minblocks)
> break;
> }
>
>
Nice catch, do you plan to do the same for ext4 ? Btw, I do not think
there is a need for new variable (free_count), you can as well do :
free_blocks -= next - start;
...
if (free_blocks < minblocks)
break;
Thanks!
-Lukas
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