On Fri, 21 Jan 2011, Tao Ma wrote:
> From: Tao Ma <boyu.mt@xxxxxxxxxx>
>
> When we trim some free blocks in a group of ext4, 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
> isn't appropriate.
>
> 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: "Theodore Ts'o" <tytso@xxxxxxx>
> Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
> ---
> fs/ext4/mballoc.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 851f49b..970e471 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4737,7 +4737,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> ext4_grpblk_t start, ext4_grpblk_t max, ext4_grpblk_t minblocks)
> {
> void *bitmap;
> - ext4_grpblk_t next, count = 0;
> + ext4_grpblk_t next, count = 0, free_count = 0;
> ext4_group_t group;
> int ret = 0;
>
> @@ -4762,6 +4762,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> break;
> count += next - start;
> }
> + free_count += next - start;
> start = next + 1;
>
> if (fatal_signal_pending(current)) {
> @@ -4775,7 +4776,7 @@ ext4_grpblk_t ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> ext4_lock_group(sb, group);
> }
>
> - if ((e4b->bd_info->bb_free - count) < minblocks)
> + if ((e4b->bd_info->bb_free - free_count) < minblocks)
> break;
> }
> ext4_unlock_group(sb, group);
>
Looks good, thanks.
-Lukas
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