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From:   Yang Shi <shy828301@gmail.com>
Date:   Wed, 10 Mar 2021 15:01:20 -0800
Message-ID: <CAHbLzkrju=bYk3mrBUxhL8uq9Q=H0Nw4dqD3sDx8G7AJY-n=Wg@mail.gmail.com>
Subject: Re: [v9 PATCH 13/13] mm: vmscan: shrink deferred objects proportional
 to priority
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Roman Gushchin <guro@fb.com>, Kirill Tkhai <ktkhai@virtuozzo.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Dave Chinner <david@fromorbit.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Mar 10, 2021 at 2:41 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Wed, Mar 10, 2021 at 1:41 PM Yang Shi <shy828301@gmail.com> wrote:
> >
> > On Wed, Mar 10, 2021 at 1:08 PM Shakeel Butt <shakeelb@google.com> wrote:
> > >
> > > On Wed, Mar 10, 2021 at 10:54 AM Yang Shi <shy828301@gmail.com> wrote:
> > > >
> > > > On Wed, Mar 10, 2021 at 10:24 AM Shakeel Butt <shakeelb@google.com> wrote:
> > > > >
> > > > > On Wed, Mar 10, 2021 at 9:46 AM Yang Shi <shy828301@gmail.com> wrote:
> > > > > >
> > > > > > The number of deferred objects might get windup to an absurd number, and it
> > > > > > results in clamp of slab objects.  It is undesirable for sustaining workingset.
> > > > > >
> > > > > > So shrink deferred objects proportional to priority and cap nr_deferred to twice
> > > > > > of cache items.
> > > > > >
> > > > > > The idea is borrowed from Dave Chinner's patch:
> > > > > > https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.com/
> > > > > >
> > > > > > Tested with kernel build and vfs metadata heavy workload in our production
> > > > > > environment, no regression is spotted so far.
> > > > >
> > > > > Did you run both of these workloads in the same cgroup or separate cgroups?
> > > >
> > > > Both are covered.
> > > >
> > >
> > > Have you tried just this patch i.e. without the first 12 patches?
> >
> > No. It could be applied without the first 12 patches, but I didn't
> > test this combination specifically since I don't think it would have
> > any difference from with the first 12 patches. I tested running the
> > test case under root memcg, it seems equal to w/o the first 12 patches
> > and the only difference is where to get nr_deferred.
>
> I am trying to measure the impact of this patch independently. One
> point I can think of is the global reclaim. The first 12 patches do
> not aim to improve the global reclaim but this patch will. I am just
> wondering what would be negative if any of this patch.

Feel free to do so. More tests from more workloads are definitely
appreciated. That could give us more confidence about this patch or
catch regression sooner.