linux-kernel - Re: [PATCH resend] memcg: introduce per-memcg reclaim interface

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Date:   Fri, 1 Apr 2022 02:23:33 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Vaibhav Jain <vaibhav@...ux.ibm.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        Jonathan Corbet <corbet@....net>, Yu Zhao <yuzhao@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface

On Fri, Apr 1, 2022 at 1:39 AM Vaibhav Jain <vaibhav@...ux.ibm.com> wrote:
>
>
> Yosry Ahmed <yosryahmed@...gle.com> writes:
> > From: Shakeel Butt <shakeelb@...gle.com>
> >
> > Introduce an memcg interface to trigger memory reclaim on a memory cgroup.
> <snip>
>
> > +
> > +     while (nr_reclaimed < nr_to_reclaim) {
> > +             unsigned long reclaimed;
> > +
> > +             if (signal_pending(current))
> > +                     break;
> > +
> > +             reclaimed = try_to_free_mem_cgroup_pages(memcg,
> > +                                             nr_to_reclaim - nr_reclaimed,
> > +                                             GFP_KERNEL, true);
> > +
> > +             if (!reclaimed && !nr_retries--)
> > +                     break;
> > +
> > +             nr_reclaimed += reclaimed;
>
> I think there should be a cond_resched() in this loop before
> try_to_free_mem_cgroup_pages() to have better chances of reclaim
> succeding early.
>
Thanks for taking the time to look at this!

I believe this loop is modeled after the loop in memory_high_write()
for the memory.high interface. Is there a reason why it should be
needed here but not there?

> <snip>
>
> --
> Cheers
> ~ Vaibhav