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

Jon Hunter
2026-04-09T20:11:19Z

On 08/04/2026 15:31, Harry Yoo (Oracle) wrote:
> On Wed, Apr 08, 2026 at 02:04:54PM +0100, Jon Hunter wrote:
>> Hi Vlastimil,
>
> Hi Jon,
>
>> 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?
>
> As far as I remember we didn't get to fully recovering the performance
> yet. Interestingly even when most of allocations go through the fastpath
> it didn't fully recover [1].
>
> [1] https://lore.kernel.org/all/abI9DKxuwl_4Gasj@hyeyoo
>
> I was suspecting it's probably because of:
> - false sharing on something (sheaves, obj metadata, etc.), or
> - suboptimal NUMA placement, or
> - something outside slab involved
>
> But I don't have enough data to back up any of these theories yet.
>
>> If there are any more patches available I will be happy to test.
>
> Thanks!
>
> Before diving deeper, could you please share the NUMA topology from
> `numactl -H` on your machine?
>
> It's probably a NUMA machine? (and hopefully not memoryless ones!)

This is not a NUMA machine, this is a Tegra234 Jetson AGX Orin board [0] ...

$ numactl -H
available: 1 nodes (0)
node 0 cpus: 0 1 2 3 4 5 6 7
node 0 size: 30517 MB
node 0 free: 29263 MB
node distances:
node 0
0: 10

Jon

[0]
https://www.nvidia.com/en-gb/autonomous-machines/embedded-systems/jetson-orin/

--
nvpublic