Re: [linus:master] [mm] f822a9a81a: stress-ng.bigheap.realloc_calls_per_sec 37.3% regression

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Aug 07, 2025 at 05:10:17PM +0100, Lorenzo Stoakes wrote:
> On Thu, Aug 07, 2025 at 09:36:38PM +0530, Dev Jain wrote:
>
> > > > > commit:
> > > > >    94dab12d86 ("mm: call pointers to ptes as ptep")
> > > > >    f822a9a81a ("mm: optimize mremap() by PTE batching")
> > > > >
> > > > > 94dab12d86cf77ff f822a9a81a31311d67f260aea96
> > > > > ---------------- ---------------------------
> > > > >           %stddev     %change         %stddev
> > > > >               \          |                \
> > > > >       13777 ± 37%     +45.0%      19979 ± 27%
> > > > > numa-vmstat.node1.nr_slab_reclaimable
> > > > >      367205            +2.3%     375703 vmstat.system.in
> > > > >       55106 ± 37%     +45.1%      79971 ± 27%
> > > > > numa-meminfo.node1.KReclaimable
> > > > >       55106 ± 37%     +45.1%      79971 ± 27%
> > > > > numa-meminfo.node1.SReclaimable
> > > > >      559381           -37.3%     350757
> > > > > stress-ng.bigheap.realloc_calls_per_sec
> > > > >       11468            +1.2%      11603 stress-ng.time.system_time
> > > > >      296.25            +4.5%     309.70 stress-ng.time.user_time
> > > > >        0.81 ±187%    -100.0%       0.00 perf-sched.sch_delay.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
> > > > >        9.36 ±165%    -100.0%       0.00 perf-sched.sch_delay.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
> > > > >        0.81 ±187%    -100.0%       0.00 perf-sched.wait_time.avg.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
> > > > >        9.36 ±165%    -100.0%       0.00 perf-sched.wait_time.max.ms.__cond_resched.zap_pte_range.zap_pmd_range.isra.0
>
> Hm is lack of zap some kind of clue here?
>
> > > > >        5.50 ± 17%    +390.9%      27.00 ± 56% perf-c2c.DRAM.local
> > > > >      388.50 ± 10%    +114.7%     834.17 ± 33% perf-c2c.DRAM.remote
> > > > >        1214 ± 13%    +107.3%       2517 ± 31% perf-c2c.HITM.local
> > > > >      135.00 ± 19%    +130.9%     311.67 ± 32% perf-c2c.HITM.remote
> > > > >        1349 ± 13%    +109.6%       2829 ± 31% perf-c2c.HITM.total
> > > >
> > > > Yeah this also looks pretty consistent too...
> > >
> > > It almost looks like some kind of NUMA effects?
> > >
> > > I would have expected that it's the overhead of the vm_normal_folio(),
> > > but not sure how that corresponds to the SLAB + local vs. remote stats.
> > > Maybe they are just noise?
> > Is there any way of making the robot test again? As you said, the only
> > suspect is vm_normal_folio(), nothing seems to pop up...
> >
>
> Not sure there's much point in that, these tests are run repeatedly and
> statistical analysis taken from them so what would another run accomplish unless
> there's something very consistently wrong with the box that happens only to
> trigger at your commit?
>
> Cheers, Lorenzo

Let me play around on my test box roughly and see if I can repro