Keep "prefetch_grp" and "nr" consistent to avoid to call
ext4_mb_prefetch_fini with non-prefetched groups.
When we step into next criteria, "prefetch_grp" is set to prefetch start
of new criteria while "nr" is number of the prefetched group in previous
criteria. If previous criteria and next criteria are both inexpensive
(< CR_GOAL_LEN_SLOW) and prefetch_ios reachs sbi->s_mb_prefetch_limit
in previous criteria, "prefetch_grp" and "nr" will be inconsistent and
may introduce unexpected cost to do ext4_mb_init_group for non-prefetched
groups.
Reset "nr" to 0 when we reset "prefetch_grp" to start of prefech in next
criteria to ensure "prefetch_grp" and "nr" are consistent.
Signed-off-by: Kemeng Shi <[email protected]>
---
fs/ext4/mballoc.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 12b3f196010b..a61fc52956b2 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2856,6 +2856,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
group = ac->ac_g_ex.fe_group;
ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
prefetch_grp = group;
+ nr = 0;
for (i = 0, new_cr = cr; i < ngroups; i++,
ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
--
2.30.0
On Wed 27-03-24 05:38:19, Kemeng Shi wrote:
> Keep "prefetch_grp" and "nr" consistent to avoid to call
> ext4_mb_prefetch_fini with non-prefetched groups.
> When we step into next criteria, "prefetch_grp" is set to prefetch start
> of new criteria while "nr" is number of the prefetched group in previous
> criteria. If previous criteria and next criteria are both inexpensive
> (< CR_GOAL_LEN_SLOW) and prefetch_ios reachs sbi->s_mb_prefetch_limit
> in previous criteria, "prefetch_grp" and "nr" will be inconsistent and
> may introduce unexpected cost to do ext4_mb_init_group for non-prefetched
> groups.
> Reset "nr" to 0 when we reset "prefetch_grp" to start of prefech in next
> criteria to ensure "prefetch_grp" and "nr" are consistent.
>
> Signed-off-by: Kemeng Shi <[email protected]>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <[email protected]>
Honza
> ---
> fs/ext4/mballoc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 12b3f196010b..a61fc52956b2 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2856,6 +2856,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> group = ac->ac_g_ex.fe_group;
> ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
> prefetch_grp = group;
> + nr = 0;
>
> for (i = 0, new_cr = cr; i < ngroups; i++,
> ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
> --
> 2.30.0
>
--
Jan Kara <[email protected]>
SUSE Labs, CR