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References: <20220331084151.2600229-1-yosryahmed@google.com> <874k3d6vuq.fsf@vajain21.in.ibm.com>
In-Reply-To: <874k3d6vuq.fsf@vajain21.in.ibm.com>
From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Fri, 1 Apr 2022 02:23:33 -0700
Message-ID: <CAJD7tka1UstKYBVrie-_1CgvtaLtVD1uwgzfk5SifxW4FQbOVw@mail.gmail.com>
Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface
To:     Vaibhav Jain <vaibhav@linux.ibm.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
        Jonathan Corbet <corbet@lwn.net>, Yu Zhao <yuzhao@google.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>
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On Fri, Apr 1, 2022 at 1:39 AM Vaibhav Jain <vaibhav@linux.ibm.com> wrote:
>
>
> Yosry Ahmed <yosryahmed@google.com> writes:
> > From: Shakeel Butt <shakeelb@google.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