Re: [PATCH v2 1/2] mm, slab: move memcg charging to post-alloc hook

[Vlastimil Babka]

On 4/3/24 1:39 PM, Aishwarya TCV wrote:
> 
> 
> On 25/03/2024 08:20, Vlastimil Babka wrote:
>> The MEMCG_KMEM integration with slab currently relies on two hooks
>> during allocation. memcg_slab_pre_alloc_hook() determines the objcg and
>> charges it, and memcg_slab_post_alloc_hook() assigns the objcg pointer
>> to the allocated object(s).
>> 
>> As Linus pointed out, this is unnecessarily complex. Failing to charge
>> due to memcg limits should be rare, so we can optimistically allocate
>> the object(s) and do the charging together with assigning the objcg
>> pointer in a single post_alloc hook. In the rare case the charging
>> fails, we can free the object(s) back.
>> 
>> This simplifies the code (no need to pass around the objcg pointer) and
>> potentially allows to separate charging from allocation in cases where
>> it's common that the allocation would be immediately freed, and the
>> memcg handling overhead could be saved.
>> 
>> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> Link: https://lore.kernel.org/all/CAHk-=whYOOdM7jWy5jdrAm8LxcgCMFyk2bt8fYYvZzM4U-zAQA@xxxxxxxxxxxxxx/
>> Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
>> Reviewed-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>
>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>> ---
>>  mm/slub.c | 180 +++++++++++++++++++++++++++-----------------------------------
>>  1 file changed, 77 insertions(+), 103 deletions(-)
> 
> Hi Vlastimil,
> 
> When running the LTP test "memcg_limit_in_bytes" against next-master
> (next-20240402) kernel with Arm64 on JUNO, oops is observed in our CI. I
> can send the full logs if required. It is observed to work fine on
> softiron-overdrive-3000.
> 
> A bisect identified 11bb2d9d91627935c63ea3e6a031fd238c846e1 as the first
> bad commit. Bisected it on the tag "next-20240402" at repo
> "https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git";.
> 
> This works fine on  Linux version v6.9-rc2

Oops, sorry, can you verify that this fixes it?
Thanks.

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