Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

From: Yosry Ahmed
Date: Wed Feb 12 2025 - 21:57:41 EST


February 12, 2025 at 6:18 PM, "Sergey Senozhatsky" <senozhatsky@xxxxxxxxxxxx> wrote:



>
> On (25/02/12 15:35), Yosry Ahmed wrote:
>
> >
> > Difference at 95.0% confidence
> >
> > -1.03219e+08 +/- 55308.7
> >
> > -27.9705% +/- 0.0149878%
> >
> > (Student's t, pooled s = 58864.4)
> >
> >
> >
> > Thanks for sharing these results, but I wonder if this will capture
> >
> > regressions from locking changes (e.g. a lock being preemtible)? IIUC
> >
> > this is counting the instructions executed in these paths, and that
> >
> > won't change if the task gets preempted. Lock contention may be captured
> >
> > as extra instructions, but I am not sure we'll directly see its effect
> >
> > in terms of serialization and delays.
> >
>
> Yeah..
>
> >
> > I think we also need some high level testing (e.g. concurrent
> >
> > swapins/swapouts) to find that out. I think that's what Kairui's testing
> >
> > covers.
> >
>
> I do a fair amount of high-level testing: heavy parallel (make -j36 and
>
> parallel dd) workloads (multiple zram devices configuration - zram0 ext4,
>
> zram1 writeback device, zram2 swap) w/ and w/o lockdep. In addition I also
>
> run these workloads under heavy memory pressure (a 4GB VM), when oom-killer
>
> starts to run around with a pair of scissors. But it's mostly regression
>
> testing.
>

If we can get some numbers from these parallel workloads that would be better than the perf stats imo.