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

Jon Hunter
2026-04-08T13:05:10Z

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@kernel.org/
>>>
>>> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
>>> ---
>>> 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

I came across Ming's report and hence, found this series. I have also
tested the 3 patches in this series and it did appear to help with one
test, but overall I am still seeing a ~25% performance regression (the
tests are taking about 25% longer to run). I am not the owner or author
of these specific tests and I have not dived into see exactly what is
taking longer, but I just know they are taking longer to run.

Anyway, I have not seen any recent updates on this, and so I am not sure
if there are any other updates or what the current status of this is?

If there are any more patches available I will be happy to test.

Thanks!
Jon

--
nvpublic