Re: [PATCH mm-unstable v2] mm/memcontrol: batch memcg charging in __memcg_slab_post_alloc_hook

["teawater" <hui.zhu@linux.dev>]

> 
> On Fri, 20 Mar 2026 10:07:45 +0800 Hui Zhu <hui.zhu@linux.dev> wrote:
> 
> > 
> > When kmem_cache_alloc_bulk() allocates multiple objects, the post-alloc
> >  hook __memcg_slab_post_alloc_hook() previously charged memcg one object
> >  at a time, even though consecutive objects may reside on slabs backed by
> >  the same pgdat node.
> >  
> >  Batch the memcg charging by scanning ahead from the current position to
> >  find a contiguous run of objects whose slabs share the same pgdat, then
> >  issue a single __obj_cgroup_charge() / __consume_obj_stock() call for
> >  the entire run. The per-object obj_ext assignment loop is preserved as-is
> >  since it cannot be further collapsed.
> >  
> >  This implements the TODO comment left in commit bc730030f956 ("memcg:
> >  combine slab obj stock charging and accounting").
> >  
> >  The existing error-recovery contract is unchanged: if size == 1 then
> >  memcg_alloc_abort_single() will free the sole object, and for larger
> >  bulk allocations kmem_cache_free_bulk() will uncharge any objects that
> >  were already charged before the failure.
> >  
> >  Benchmark using kmem_cache_alloc_bulk() with SLAB_ACCOUNT
> >  (iters=100000):
> >  
> >  bulk=32 before: 215 ns/object after: 174 ns/object (-19%)
> >  bulk=1 before: 344 ns/object after: 335 ns/object ( ~)
> >  
> >  No measurable regression for bulk=1, as expected.
> > 

Hi Andrew,

> I noticed that the AI review of your v1 patch reported a few potential
> issues:
>  https://sashiko.dev/#/patchset/20260316084839.1342163-1-hui.zhu@linux.dev
> 
> Can you please take a look, see if any of this is valid for v2?
> 
> Unfortunately the bot wasn't able to check v2 because it couldn't get
> the patch to apply. I've checked that this patch does apply cleanly to
> current mm-stable, which is on the bot's try-to-apply list. So if you
> wish to get checking of the latest patch, please send us a v3 and that
> will trigger a retry.

I will send a v3 to make sure the patch is OK.

Best,
Hui

>