On 4/26/23 17:03, Baolin Wang wrote:
> This reverts commit 95e7a450b8190673675836bfef236262ceff084a.
>
> When I tested thpscale with v6.3 kernel, I found the compaction efficiency
> had a great regression compared to v6.2-rc1 kernel. See below numbers:
> v6.2-rc v6.3
> Percentage huge-3 81.35 ( 0.00%) 32.97 ( -59.47%)
> Percentage huge-5 89.92 ( 0.00%) 41.70 ( -53.63%)
> Percentage huge-7 92.41 ( 0.00%) 34.08 ( -63.12%)
> Percentage huge-12 90.29 ( 0.00%) 41.10 ( -54.49%)
> Percentage huge-18 82.38 ( 0.00%) 41.24 ( -49.95%)
> Percentage huge-24 80.34 ( 0.00%) 35.99 ( -55.20%)
> Percentage huge-30 88.90 ( 0.00%) 44.20 ( -50.28%)
> Percentage huge-32 90.69 ( 0.00%) 79.57 ( -12.25%)
>
> Ops Compaction stalls 113790.00 207099.00
> Ops Compaction success 33983.00 19488.00
> Ops Compaction failures 79807.00 187611.00
> Ops Compaction efficiency 29.86 9.41
>
> After some investigation, I found the commit 95e7a450b819
> ("Revert mm/compaction: fix set skip in fast_find_migrateblock") caused
> the regression. This commit revert the commit 7efc3b726103 ("mm/compaction:
> fix set skip in fast_find_migrateblock") to fix a CPU stalling issue, which
> is caused by compaction stucked in repeating fast_find_migrateblock().
>
> And now the compaction stalling issue is addressed by commit cfccd2e63e7e
> ("mm, compaction: finish pageblocks on complete migration failure"). So
IIRC at that time I was pointing out some scenarios that could make the
problem appear even after that commit, and we wanted to revisit that
when Mel is back.
> we should revert the temporary fix by commit 95e7a450b819, since the
> fast pfn found by fast_find_migrateblock() really can help to isolate
> some migratable pages.
So thanks for the reminder, yet we should make sure the fix is complete
before removing the workaround.
> After reverting the commit, the regression has gone.
> v6.2-rc1 v6.3 v6.3_patched
> Percentage huge-3 81.35 ( 0.00%) 32.97 ( -59.47%) 87.78 ( 7.90%)
> Percentage huge-5 89.92 ( 0.00%) 41.70 ( -53.63%) 89.68 ( -0.27%)
> Percentage huge-7 92.41 ( 0.00%) 34.08 ( -63.12%) 85.89 ( -7.05%)
> Percentage huge-12 90.29 ( 0.00%) 41.10 ( -54.49%) 94.10 ( 4.22%)
> Percentage huge-18 82.38 ( 0.00%) 41.24 ( -49.95%) 85.06 ( 3.25%)
> Percentage huge-24 80.34 ( 0.00%) 35.99 ( -55.20%) 84.38 ( 5.02%)
> Percentage huge-30 88.90 ( 0.00%) 44.20 ( -50.28%) 95.54 ( 7.48%)
> Percentage huge-32 90.69 ( 0.00%) 79.57 ( -12.25%) 92.30 ( 1.78%)
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> mm/compaction.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 33650541bebc..567c8d41d01e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1860,7 +1860,6 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
> pfn = cc->zone->zone_start_pfn;
> cc->fast_search_fail = 0;
> found_block = true;
> - set_pageblock_skip(freepage);
> break;
> }
> }
