linux-kernel - Re: [PATCH v8 1/6] list_lru: allows explicit memcg and NUMA node selection

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Message-ID: <CAKEwX=MV-F50i_=sZ0unfbgjrdxSTio00c4xTM19113BAN3-wA@mail.gmail.com>
Date:   Thu, 30 Nov 2023 12:07:41 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        cerasuolodomenico@...il.com, yosryahmed@...gle.com,
        sjenning@...hat.com, ddstreet@...e.org, vitaly.wool@...sulko.com,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH v8 1/6] list_lru: allows explicit memcg and NUMA node selection

On Thu, Nov 30, 2023 at 11:57 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Thu, Nov 30, 2023 at 11:40:18AM -0800, Nhat Pham wrote:
> > This patch changes list_lru interface so that the caller must explicitly
> > specify numa node and memcg when adding and removing objects. The old
> > list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and
> > list_lru_del_obj(), respectively.
>
> Wouldn't it be better to add list_lru_add_memcg() and
> list_lru_del_memcg() and have:
>
> +bool list_lru_del(struct list_lru *lru, struct list_head *item)
> +{
> +       int nid = page_to_nid(virt_to_page(item));
> +       struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
> +               mem_cgroup_from_slab_obj(item) : NULL;
> +
> +       return list_lru_del_memcg(lru, item, nid, memcg);
> +}
>
> Seems like _most_ callers will want the original versions and only
> a few will want the explicit memcg/nid versions.  No?
>

I actually did something along that line in earlier iterations of this
patch series (albeit with poorer naming - __list_lru_add() instead of
list_lru_add_memcg()). The consensus after some back and forth was
that the original list_lru_add() was not a very good design (the
better one was this new version that allows for explicit numa/memcg
selection). So I agreed to fix it everywhere as a prep patch.

I don't have strong opinions here to be completely honest, but I do
think this new API makes more sense (at the cost of quite a bit of
elbow grease to fix every callsites and extra reviewing).