linux-kernel - Re: [PATCH v3 6/8] workingset: memcg: sleep when flushing stats in workingset

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Message-ID: <CAJD7tkZ=o42N_45LxRPg=oOg56Lqn-wqT_0JJUPPoKOB+ig2JQ@mail.gmail.com>
Date:   Wed, 5 Apr 2023 01:02:01 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vasily Averin <vasily.averin@...ux.dev>,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3 6/8] workingset: memcg: sleep when flushing stats in workingset_refault()

On Wed, Apr 5, 2023 at 1:00 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> On Tue, Apr 04, 2023 at 11:09:02AM -0700, Yosry Ahmed <yosryahmed@...gle.com> wrote:
> > IIUC there are multiple places where we can sleep in this path, we can
> > sleep waiting for a page to be read from disk, we can sleep during
> > allocating the page to read into, and IIUC the allocations on the
> > fault path can even run into reclaim, going into the vmscan code. So
> > there are precedents, but I am not sure if that's enough argument.
>
> I expect it'd depend on the proportion of the slow/fast paths.
> OK, let's see how it turns out in wider population.

Agreed. It also depends on the number of memcgs and how much the
periodic flusher is keeping up. I think no amount of testing will
cover all or even most workloads.

>
> Thanks,
> Michal