Re: [PATCH 0/3] slab: support memoryless nodes with sheaves

[Jon Hunter]

On 08/04/2026 15:06, Hao Li wrote:
> On Wed, Apr 08, 2026 at 02:04:54PM +0100, Jon Hunter wrote:
> > Hi Vlastimil,
> >
> > On 11/03/2026 17:22, Vlastimil Babka (SUSE) wrote:
> > > On 3/11/26 10:49, Ming Lei wrote:
> > > > On Wed, Mar 11, 2026 at 09:25:54AM +0100, Vlastimil Babka (SUSE) wrote:
> > > > > This is the draft patch from [1] turned into a proper series with
> > > > > incremental changes. It's based on v7.0-rc3. It's too intrusive for a
> > > > > 7.0 hotfix, so we'll only be able to fix/reduce the regression in 7.1. I
> > > > > hope it's acceptable given it's a non-standard configuration, 7.0 is not
> > > > > a LTS, and it's a perf regression, not functionality.
> > > > >
> > > > > Ming can you please retest this on top of v7.0-rc3, which already has
> > > > > fb1091febd66 ("mm/slab: allow sheaf refill if blocking is not
> > > > > allowed"). Separate data point for v7.0-rc3 could be also useful.
> > > > >
> > > > > [1] https://lore.kernel.org/all/c6a01f7e-c6eb-454b-9b9e-734526dd659d@xxxxxxxxxx/
> > > > >
> > > > > Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
> > > > > ---
> > > > > Vlastimil Babka (SUSE) (3):
> > > > >         slab: decouple pointer to barn from kmem_cache_node
> > > > >         slab: create barns for online memoryless nodes
> > > > >         slab: free remote objects to sheaves on memoryless nodes
> > > >
> > > > Hi Vlastimil and Guys,
> > > >
> > > > I re-run the test case used in https://lore.kernel.org/all/aZ0SbIqaIkwoW2mB@fedora/
> > > >
> > > > - v6.19-rc5: 34M
> > > >
> > > > - 815c8e35511d Merge branch 'slab/for-7.0/sheaves' into slab/for-next: 13M
> > > >
> > > > - v7.0-rc3: 13M
> > >
> > > Thanks, that's in line with your previous testing of "mm/slab: allow sheaf
> > > refill if blocking is not allowed" making no difference here. At least we
> > > just learned it helps other benchmarks :)
> > >
> > > > - v7.0-rc3 + the three patches: 24M
> > >
> > > OK. So now it might be really the total per-cpu caching capacity difference.
> >
> >
> > I have also observed a performance regresssion for Linux v7.0-rc for some
> > graphics related tests we run. I bisected to ...
> >
> > # first bad commit: [e47c897a29491ade20b27612fdd3107c39a07357] slab: add
> > sheaves to most caches
>
> Hi, Jon
>
> Thanks for the reporting.
> This first bad commit is surprising. In theory, this commit seems couldn't hurt
> performance.
> Could you possibly manually switch commits to verify this bad commit again,
> without using git bisect?

So I went back and checked out commit 
e47c897a29491ade20b27612fdd3107c39a07357 ("slab: add
sheaves to most caches") confirmed that the problem exists there and 
then reverted that and confirmed that I no longer see the problem.

Jon

--
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