linux-kernel - Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation

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Message-ID: <YliFs3NOHeo2LeXl@google.com>
Date:   Thu, 14 Apr 2022 14:36:03 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Barry Song <21cnbao@...il.com>
Cc:     Stephen Rothwell <sfr@...hwell.id.au>,
        Linux-MM <linux-mm@...ck.org>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aneesh Kumar <aneesh.kumar@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Michael Larabel <Michael@...haellarabel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Will Deacon <will@...nel.org>,
        Ying Huang <ying.huang@...el.com>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Page Reclaim v2 <page-reclaim@...gle.com>,
        x86 <x86@...nel.org>, Brian Geffon <bgeffon@...gle.com>,
        Jan Alexander Steffens <heftig@...hlinux.org>,
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        Shuang Zhai <szhai2@...rochester.edu>,
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        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation

On Thu, Apr 14, 2022 at 06:03:10PM +1200, Barry Song wrote:
> 
> On Thu, Apr 7, 2022 at 3:16 PM Yu Zhao <yuzhao@...gle.com> wrote:
> >
> > +
> > +static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
> > +                         int *type_scanned, struct list_head *list)
> > +{
> > +       int i;
> > +       int type;
> > +       int scanned;
> > +       int tier = -1;
> > +       DEFINE_MIN_SEQ(lruvec);
> > +
> > +       VM_BUG_ON(!seq_is_valid(lruvec));
> > +
> > +       /*
> > +        * Try to make the obvious choice first. When anon and file are both
> > +        * available from the same generation, interpret swappiness 1 as file
> > +        * first and 200 as anon first.
> > +        */
> 
> Has this changed the ABI of swapiness?

No.

> or it is only something
> meaningful for the internal code?

This is how swappiness is interpreted.

> if so, can we rename it to
> something else? otherwise, it is quite confusing.

Feel free to suggest something.

> it seems 1 is set internally as a magic number here:
> +static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct
> scan_control *sc)
> +{
> + ...
> + else if (!cgroup_reclaim(sc) && get_swappiness(lruvec, sc))
> + swappiness = 1;
> + else
> + swappiness = 0;
> + }
> obviously this swappiness is neither /proc/sys/vm/swappiness  nor
> /sys/fs/cgroup/memory/<group>/>memory.swappiness, right?

Right.

> > @@ -3928,6 +4726,11 @@ static void age_active_anon(struct pglist_data *pgdat,
> >         struct mem_cgroup *memcg;
> >         struct lruvec *lruvec;
> >
> > +       if (lru_gen_enabled()) {
> > +               lru_gen_age_node(pgdat, sc);
> > +               return;
> > +       }
> 
> is it really a good place for  lru_gen_age_node() since the function
> is named age_active_anon()
> but here you are doing aging for both anon and file pages?

Yes.

> obviously
> lru_gen_age_node() is not
> doing "age active anon".

We can rename it if you have something in mind.