linux-kernel - Re: [v9 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority

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Message-ID: <CALvZod5B+JZT2WK=_fKH7tfpXG=NLhwhN=Y83y4+HmsG8TT2LA@mail.gmail.com>
Date:   Wed, 10 Mar 2021 14:40:59 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Roman Gushchin <guro@...com>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Chinner <david@...morbit.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v9 PATCH 13/13] mm: vmscan: shrink deferred objects proportional
 to priority

On Wed, Mar 10, 2021 at 1:41 PM Yang Shi <shy828301@...il.com> wrote:
>
> On Wed, Mar 10, 2021 at 1:08 PM Shakeel Butt <shakeelb@...gle.com> wrote:
> >
> > On Wed, Mar 10, 2021 at 10:54 AM Yang Shi <shy828301@...il.com> wrote:
> > >
> > > On Wed, Mar 10, 2021 at 10:24 AM Shakeel Butt <shakeelb@...gle.com> wrote:
> > > >
> > > > On Wed, Mar 10, 2021 at 9:46 AM Yang Shi <shy828301@...il.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.