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

Jon Hunter
2026-04-09T20:02:41Z

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@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
>
> 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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