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From:   Joonsoo Kim <js1304@gmail.com>
Date:   Tue, 3 Mar 2020 08:31:25 +0900
Message-ID: <CAAmzW4MCi9xqMCvFVRT6=SUjJgzprOoFhZe4BdXa7wH6jPYqBg@mail.gmail.com>
Subject: Re: [PATCH v2 0/9] workingset protection/detection on the anonymous
 LRU list
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>, kernel-team@lge.com,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
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2020=EB=85=84 2=EC=9B=94 28=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 8:36, A=
ndrew Morton <akpm@linux-foundation.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=
=B1:
>
> On Thu, 27 Feb 2020 08:48:06 -0500 Johannes Weiner <hannes@cmpxchg.org> w=
rote:
>
> > > It sounds like the above simple aging changes provide most of the
> > > improvement, and that the workingset changes are less beneficial and =
a
> > > bit more risky/speculative?
> > >
> > > If so, would it be best for us to concentrate on the aging changes
> > > first, let that settle in and spread out and then turn attention to t=
he
> > > workingset changes?
> >
> > Those two patches work well for some workloads (like the benchmark),
> > but not for others. The full patchset makes sure both types work well.
> >
> > Specifically, the existing aging strategy for anon assumes that most
> > anon pages allocated are hot. That's why they all start active and we
> > then do second-chance with the small inactive LRU to filter out the
> > few cold ones to swap out. This is true for many common workloads.
> >
> > The benchmark creates a larger-than-memory set of anon pages with a
> > flat access profile - to the VM a flood of one-off pages. Joonsoo's
> > first two patches allow the VM to usher those pages in and out of
> > memory very quickly, which explains the throughput boost. But it comes
> > at the cost of reducing space available to hot anon pages, which will
> > regress others.
> >
> > Joonsoo's full patchset makes the VM support both types of workloads
> > well: by putting everything on the inactive list first, one-off pages
> > can move through the system without disturbing the hot pages. And by
> > supplementing the inactive list with non-resident information, he can
> > keep it tiny without the risk of one-off pages drowning out new hot
> > pages. He can retain today's level of active page protection and
> > detection, while allowing one-off pages to move through quickly.
>
> Helpful, thanks.
>
> At v2 with no evident review input I'd normally take a pass at this
> stage.  But given all the potential benefits, perhaps I should be more
> aggressive here?

I hope so. It would boost the review. :)

Thanks.