linux-kernel - Re: [PATCH 3/3] mm, lru_gen: try to prefetch next page when canning LRU

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Message-ID: <CAOUHufZmwaos=6reZSbs53e5TM8nbK-u=1Q_god1fWPz-o_wLw@mail.gmail.com>
Date: Sun, 24 Dec 2023 23:54:35 -0700
From: Yu Zhao <yuzhao@...gle.com>
To: Kairui Song <kasong@...cent.com>, Matthew Wilcox <willy@...radead.org>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm, lru_gen: try to prefetch next page when canning LRU

On Sun, Dec 24, 2023 at 11:41 PM Yu Zhao <yuzhao@...gle.com> wrote:
>
> On Fri, Dec 22, 2023 at 3:24 AM Kairui Song <ryncsn@...il.com> wrote:
> >
> > From: Kairui Song <kasong@...cent.com>
> >
> > Prefetch for inactive/active LRU have been long exiting, apply the same
> > optimization for MGLRU.
>
> I seriously doubt that prefetch helps in this case.
>
> Willy, any thoughts on this? Thanks.
>
> > Tested in a 4G memcg on a EPYC 7K62 with:
> >
> >   memcached -u nobody -m 16384 -s /tmp/memcached.socket \
> >     -a 0766 -t 16 -B binary &
> >
> >   memtier_benchmark -S /tmp/memcached.socket \
> >     -P memcache_binary -n allkeys \
> >     --key-minimum=1 --key-maximum=16000000 -d 1024 \
> >     --ratio=1:0 --key-pattern=P:P -c 2 -t 16 --pipeline 8 -x 6
> >
> > Average result of 18 test runs:
> >
> > Before:           44017.78 Ops/sec
> > After patch 1-3:  44890.50 Ops/sec (+1.8%)

This patch itself only brought a 0.17% "improvement", which I'm
99.999% sure is just noise.