Re: [PATCH v5 02/16] mm: introduce kmem_cache_alloc_lru

[Muchun Song <songmuchun@bytedance.com>]

On Fri, Jan 7, 2022 at 11:05 AM Roman Gushchin <guro@fb.com> wrote:
>
[...]
> >  /*
> >   * struct kmem_cache related prototypes
> > @@ -425,6 +426,8 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
> >
> >  void *__kmalloc(size_t size, gfp_t flags) __assume_kmalloc_alignment __alloc_size(1);
> >  void *kmem_cache_alloc(struct kmem_cache *s, gfp_t flags) __assume_slab_alignment __malloc;
> > +void *kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> > +                        gfp_t gfpflags) __assume_slab_alignment __malloc;
>
> I'm not a big fan of this patch: I don't see why preparing the lru
> infrastructure has to be integrated that deep into the slab code.
>
> Why can't kmem_cache_alloc_lru() be a simple wrapper like (pseudo-code):
>   void *kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>                            gfp_t gfpflags) {
>         if (necessarily)
>            prepare_lru_infra();
>         return kmem_cache_alloc();
>   }

Hi Roman,

Actually, it can. But there is going to be some redundant code similar
like memcg_slab_pre_alloc_hook() does to detect the necessity of
prepare_lru_infra() in the new scheme of kmem_cache_alloc_lru().
I just want to reduce the redundant overhead.

Thanks.