On Wed, Apr 26, 2023 at 05:10:14PM +0200, Vlastimil Babka wrote:
> 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.
>
Yes, I've prototyped the fix against 6.3-rc7 and the revert is at the
end but the revert on its own has the potential for causing problems. The
series needs to be rebased, retested and posted. What I last tested
should show up shortly at
https://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git/ mm-follupfastmigrate-v1r1
--
Mel Gorman
SUSE Labs
