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

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Message-ID: <25268fbedb82a06ba0c13e2c490b164846ef508b@linux.dev>
Date: Thu, 13 Feb 2025 02:57:28 +0000
From: "Yosry Ahmed" <yosry.ahmed@...ux.dev>
To: "Sergey Senozhatsky" <senozhatsky@...omium.org>
Cc: "Sergey Senozhatsky" <senozhatsky@...omium.org>, "Andrew Morton"
 <akpm@...ux-foundation.org>, "Minchan Kim" <minchan@...nel.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, "Kairui Song"
 <ryncsn@...il.com>
Subject: Re: [PATCHv4 14/17] zsmalloc: make zspage lock preemptible

February 12, 2025 at 6:18 PM, "Sergey Senozhatsky" <senozhatsky@...omium.org> 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.