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

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Date:   Fri, 15 Apr 2022 22:26:07 +1200
From:   Barry Song <21cnbao@...il.com>
To:     Yu Zhao <yuzhao@...gle.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>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Steven Barrett <steven@...uorix.net>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Daniel Byrne <djbyrne@....edu>,
        Donald Carr <d@...os-reins.com>,
        Holger Hoffstätte <holger@...lied-asynchrony.com>,
        Konstantin Kharlamov <Hi-Angel@...dex.ru>,
        Shuang Zhai <szhai2@...rochester.edu>,
        Sofia Trinh <sofia.trinh@....works>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation

On Fri, Apr 15, 2022 at 8:36 AM Yu Zhao <yuzhao@...gle.com> wrote:
>
> 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.

i wonder if we can directly do:

if (lru_gen_enabled())
      lru_gen_age_node(pgdat, sc);
else
     age_active_anon();

rather than:

/*
 * Do some background aging of the anon list, to give
 * pages a chance to be referenced before reclaiming. All
 * pages are rotated regardless of classzone as this is
 * about consistent aging.
 */
age_active_anon()
{
    if (lru_gen_enabled())
          return lru_gen_age_node(pgdat, sc);
}

the comment above makes no sense to lru_gen_age_node(pgdat, sc);

another way is that we can add a wrapper for them as below,
age_node()
{
    if (lru_gen_enabled())
          return lru_gen_age_node(pgdat, sc);
    age_active_anon();
}

Thanks
Barry