linux-kernel - Re: [PATCH 2/3] mm, lru_gen: move pages in bulk when aging

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Date: Mon, 25 Dec 2023 15:01:57 +0800
From: Kairui Song <ryncsn@...il.com>
To: Yu Zhao <yuzhao@...gle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm, lru_gen: move pages in bulk when aging

Yu Zhao <yuzhao@...gle.com> 于2023年12月25日周一 14:58写道：
>
> On Fri, Dec 22, 2023 at 3:24 AM Kairui Song <ryncsn@...il.com> wrote:
> >
> > From: Kairui Song <kasong@...cent.com>
> >
> > Another overhead of aging is page moving. Actually, in most cases,
> > pages are being moved to the same gen after folio_inc_gen is called,
> > especially the protected pages.  So it's better to move them in bulk.
> >
> > This also has a good effect on LRU ordering. Currently when MGLRU
> > ages, it walks the LRU backward, and the protected pages are moved to
> > the tail of newer gen one by one, which reverses the order of pages in
> > LRU. Moving them in batches can help keep their order, only in a small
> > scope though due to the scan limit of MAX_LRU_BATCH pages.
> >
> > After this commit, we can see a performance gain:
> >
> > 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 1-2:  44810.01 Ops/sec (+1.8%)
>
> Was it tested with CONFIG_DEBUG_LIST=y?
>

Hi, CONFIG_DEBUG_LIST is disabled here.

> Also, the (44810.01-44687.08)/44687.08=0.0027 improvement also sounded
> like a noise to me.
>