linux-kernel - Re: [PATCH 8/8] mm: Remove PG

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Message-ID: <CAOUHufY+BViSYS14tfN8EOhuE05KneG2syHhVCyFPppkmDH=aQ@mail.gmail.com>
Date: Tue, 14 Jan 2025 10:01:52 -0700
From: Yu Zhao <yuzhao@...gle.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Matthew Wilcox <willy@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jens Axboe <axboe@...nel.dk>, "Jason A. Donenfeld" <Jason@...c4.com>, 
	Andi Shyti <andi.shyti@...ux.intel.com>, Chengming Zhou <chengming.zhou@...ux.dev>, 
	Christian Brauner <brauner@...nel.org>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Dan Carpenter <dan.carpenter@...aro.org>, David Airlie <airlied@...il.com>, 
	David Hildenbrand <david@...hat.com>, Hao Ge <gehao@...inos.cn>, 
	Jani Nikula <jani.nikula@...ux.intel.com>, Johannes Weiner <hannes@...xchg.org>, 
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Josef Bacik <josef@...icpanda.com>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Miklos Szeredi <miklos@...redi.hu>, Nhat Pham <nphamcs@...il.com>, 
	Oscar Salvador <osalvador@...e.de>, Ran Xiaokai <ran.xiaokai@....com.cn>, 
	Rodrigo Vivi <rodrigo.vivi@...el.com>, Simona Vetter <simona@...ll.ch>, 
	Steven Rostedt <rostedt@...dmis.org>, Tvrtko Ursulin <tursulin@...ulin.net>, 
	Vlastimil Babka <vbabka@...e.cz>, Yosry Ahmed <yosryahmed@...gle.com>, intel-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 8/8] mm: Remove PG_reclaim

On Tue, Jan 14, 2025 at 1:30 AM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> On Mon, Jan 13, 2025 at 03:28:43PM +0000, Matthew Wilcox wrote:
> > On Mon, Jan 13, 2025 at 11:34:53AM +0200, Kirill A. Shutemov wrote:
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index caadbe393aa2..beba72da5e33 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -686,6 +686,8 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
> > >             folio_set_young(newfolio);
> > >     if (folio_test_idle(folio))
> > >             folio_set_idle(newfolio);
> > > +   if (folio_test_readahead(folio))
> > > +           folio_set_readahead(newfolio);
> > >
> > >     folio_migrate_refs(newfolio, folio);
> > >     /*
> >
> > Not a problem with this patch ... but aren't we missing a
> > test_dropbehind / set_dropbehind pair in this function?  Or are we
> > prohibited from migrating a folio with the dropbehind flag set
> > somewhere?
>
> Hm. Good catch.
>
> We might want to drop clean dropbehind pages instead migrating them.
>
> But I am not sure about dirty ones. With slow backing storage it might be
> better for the system to migrate them instead of keeping them in the old
> place for potentially long time.
>
> Any opinions?
>
> > > +++ b/mm/swap.c
> > > @@ -221,22 +221,6 @@ static void lru_move_tail(struct lruvec *lruvec, struct folio *folio)
> > >     __count_vm_events(PGROTATED, folio_nr_pages(folio));
> > >  }
> > >
> > > -/*
> > > - * Writeback is about to end against a folio which has been marked for
> > > - * immediate reclaim.  If it still appears to be reclaimable, move it
> > > - * to the tail of the inactive list.
> > > - *
> > > - * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
> > > - */
> > > -void folio_rotate_reclaimable(struct folio *folio)
> > > -{
> > > -   if (folio_test_locked(folio) || folio_test_dirty(folio) ||
> > > -       folio_test_unevictable(folio))
> > > -           return;
> > > -
> > > -   folio_batch_add_and_move(folio, lru_move_tail, true);
> > > -}
> >
> > I think this is the last caller of lru_move_tail(), which means we can
> > get rid of fbatches->lru_move_tail and the local_lock that protects it.
> > Or did I miss something?
>
> I see lru_move_tail() being used by lru_add_drain_cpu().

That can be deleted too, since you've already removed the producer to
fbatches->lru_move_tail.