linux-kernel - Re: [PATCH v5 02/16] mm: introduce kmem_cache_alloc

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Message-ID: <CAMZfGtWmwTLHdO6acx9_+nR68j-v9SKjMsq-0v4ZDeQORgaQ=w@mail.gmail.com>
Date:   Sun, 9 Jan 2022 14:21:22 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Roman Gushchin <guro@...com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yang Shi <shy828301@...il.com>, Alex Shi <alexs@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>,
        Dave Chinner <david@...morbit.com>,
        trond.myklebust@...merspace.com, anna.schumaker@...app.com,
        jaegeuk@...nel.org, chao@...nel.org,
        Kari Argillander <kari.argillander@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-nfs@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        Fam Zheng <fam.zheng@...edance.com>,
        Muchun Song <smuchun@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v5 02/16] mm: introduce kmem_cache_alloc_lru

On Fri, Jan 7, 2022 at 11:05 AM Roman Gushchin <guro@...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.