linux-kernel - Re: [PATCH v5 00/11] Use obj_cgroup APIs to charge the LRU pages

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Message-ID: <YpWBfPviP0TTSF4d@carbon>
Date:   Mon, 30 May 2022 19:46:20 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Muchun Song <songmuchun@...edance.com>, hannes@...xchg.org,
        mhocko@...nel.org, shakeelb@...gle.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com, longman@...hat.com
Subject: Re: [PATCH v5 00/11] Use obj_cgroup APIs to charge the LRU pages

On Mon, May 30, 2022 at 02:17:11PM -0700, Andrew Morton wrote:
> On Mon, 30 May 2022 15:49:08 +0800 Muchun Song <songmuchun@...edance.com> wrote:
> 
> > This version is rebased on v5.18.
> 
> Not a great choice of base, really.  mm-stable or mm-unstable or
> linux-next or even linus-of-the-day are all much more up to date.
> 
> Although the memcg reviewer tags are pretty thin, I was going to give
> it a run.  But after fixing a bunch of conflicts I got about halfway
> through then gave up on a big snarl in get_obj_cgroup_from_current().
> 
> > RFC v1: https://lore.kernel.org/all/20210330101531.82752-1-songmuchun@bytedance.com/
> 
> Surprising, that was over a year ago.  Why has is taken so long?

It's partially my fault: I was thinking (and to some extent still are)
that using objcg is not the best choice long-term and was pushing on the
idea to used per-memcg lru vectors as intermediate objects instead.
But it looks like I underestimated the complexity and a potential overhead
of this solution.

The objcg-based approach can solve the problem right now and it shouldn't
bring any long-term issues. So I asked Muchun to revive the patchset.

Thanks!