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From: Kairui Song <ryncsn@gmail.com>
Date: Wed, 27 Dec 2023 18:22:46 +0800
Message-ID: <CAMgjq7Dzf48pu5mJQFdqLxW9c=1N0jC4u53xY3fALBvv9Yrq1g@mail.gmail.com>
Subject: Re: [PATCH 1/3] mm, lru_gen: batch update counters on againg
To: Chris Li <chrisl@kernel.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, 
	Yu Zhao <yuzhao@google.com>, linux-kernel@vger.kernel.org
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Chris Li <chrisl@kernel.org> =E4=BA=8E2023=E5=B9=B412=E6=9C=8827=E6=97=A5=
=E5=91=A8=E4=B8=89 07:43=E5=86=99=E9=81=93=EF=BC=9A
>
> Hi Kairui,
>
> Some early feedback on your patch. I am still working  my way through
> your patches.
> Might have more questions.

Hi Chris,

Thanks for the review.

> On Fri, Dec 22, 2023 at 2:24=E2=80=AFAM Kairui Song <ryncsn@gmail.com> wr=
ote:
> >
> > From: Kairui Song <kasong@tencent.com>
> >
> > When lru_gen is aging, it will update mm counters page by page,
> > which causes a higher overhead if age happens frequently or there
> > are a lot of pages in one generation getting moved.
> > Optimize this by doing the counter update in batch.
> >
> > Although most __mod_*_state has its own caches the overhead
> > is still observable.
> >
> > 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=3D1 --key-maximum=3D16000000 -d 1024 \
> >     --ratio=3D1:0 --key-pattern=3DP:P -c 2 -t 16 --pipeline 8 -x 6
> >
> > Average result of 18 test runs:
> >
> > Before: 44017.78 Ops/sec
> > After:  44687.08 Ops/sec (+1.5%)
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
> > ---
> >  mm/vmscan.c | 64 +++++++++++++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 55 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index b4ca3563bcf4..e3b4797b9729 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -3095,9 +3095,47 @@ static int folio_update_gen(struct folio *folio,=
 int gen)
> >         return ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> >  }
> >
> > +/*
> > + * Update LRU gen in batch for each lru_gen LRU list. The batch is lim=
ited to
> > + * each gen / type / zone level LRU. Batch is applied after finished o=
r aborted
> > + * scanning one LRU list.
> > + */
> > +struct gen_update_batch {
> > +       int delta[MAX_NR_GENS];
> > +};
> > +
> > +static void lru_gen_update_batch(struct lruvec *lruvec, bool type, int=
 zone,
> "type" need to be int, it is either  LRU_GEN_FILE or LRU_GEN_ANON.

Yes, I'll update it with some more test results later.