Re: [PATCH 2/4] mm/slub: introduce __kmem_cache_free_bulk() without free hooks

[Vlastimil Babka]

On 12/5/23 09:19, Chengming Zhou wrote:
> On 2023/12/5 03:34, Vlastimil Babka wrote:
>> Currently, when __kmem_cache_alloc_bulk() fails, it frees back the
>> objects that were allocated before the failure, using
>> kmem_cache_free_bulk(). Because kmem_cache_free_bulk() calls the free
>> hooks (KASAN etc.) and those expect objects that were processed by the
>> post alloc hooks, slab_post_alloc_hook() is called before
>> kmem_cache_free_bulk().
>> 
>> This is wasteful, although not a big concern in practice for the rare
>> error path. But in order to efficiently handle percpu array batch refill
>> and free in the near future, we will also need a variant of
>> kmem_cache_free_bulk() that avoids the free hooks. So introduce it now
>> and use it for the failure path.
>> 
>> As a consequence, __kmem_cache_alloc_bulk() no longer needs the objcg
>> parameter, remove it.
> 
> The objects may have been charged before, but it seems __kmem_cache_alloc_bulk()
> forget to uncharge them? I can't find "uncharge" in do_slab_free(), or maybe
> the bulk interface won't be used on chargeable slab?

You're right! I missed that the memcg_pre_alloc_hook() already does the
charging, so we need to uncharge. How does this look? Thanks for noticing!

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