linux-kernel - Re: [PATCH] mm/damon/paddr: fix pin page problem

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Message-ID: <940f661c65e4fed70bd90bc6e4b6723e4f95b11f.camel@mediatek.com>
Date:   Wed, 22 Feb 2023 06:26:18 +0000
From:   Andrew Yang (楊智強) 
        <Andrew.Yang@...iatek.com>
To:     "sj@...nel.org" <sj@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "damon@...ts.linux.dev" <damon@...ts.linux.dev>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Casper Li (李中榮) <casper.li@...iatek.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH] mm/damon/paddr: fix pin page problem

On Tue, 2023-02-21 at 18:35 +0000, SeongJae Park wrote:
> Hi Andrew,
> 
> 
> On Tue, 21 Feb 2023 17:03:13 +0800 Andrew Yang <
> andrew.yang@...iatek.com> wrote:
> 
> > From: "andrew.yang" <andrew.yang@...iatek.com>
> > 
> > damon_get_page() would always increase page _refcount and
> > isolate_lru_page() would increase page _refcount if the page's lru
> > flag is set.
> > 
> > If a unevictable page isolated successfully, there will be two more
> > _refcount. The one from isolate_lru_page() will be decreased in
> > putback_lru_page(), but the other one from damon_get_page() will be
> > left behind. This causes a pin page.
> > 
> > Whatever the case, the _refcount from damon_get_page() should be
> > decreased.
> 
> Thank you for finding this issue!  I think the David suggested
> subject[1] is
> better, though.
> 
> I think we could add below Fixes: and Cc: tags?
> 
> Fixes: 57223ac29584 ("mm/damon/paddr: support the pageout scheme")
> Cc: <stable@...r.kernel.org> # 5.16.x
> 
> > 
> > Signed-off-by: andrew.yang <andrew.yang@...iatek.com>
> > ---
> >  mm/damon/paddr.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> > index e1a4315c4be6..56d8abd08fb1 100644
> > --- a/mm/damon/paddr.c
> > +++ b/mm/damon/paddr.c
> > @@ -223,8 +223,8 @@ static unsigned long damon_pa_pageout(struct
> > damon_region *r)
> >  			putback_lru_page(page);
> >  		} else {
> >  			list_add(&page->lru, &page_list);
> > -			put_page(page);
> >  		}
> > +		put_page(page);
> 
> Seems your patch is not based on mm-unstable tree[2].  Could you
> please rebase
> on it?
> 
> Also, let's remove the braces for the single statements[3].
> 
> [1] 
> https://lore.kernel.org/damon/1b3e8e88-ed5c-7302-553f-4ddb3400d466@redhat.com/
> [2] 
> https://urldefense.com/v3/__https://docs.kernel.org/next/mm/damon/maintainer-profile.html*scm-trees__;Iw!!CTRNKA9wMg0ARbw!jlYra3CQPXNsppOWspkAkRO2AfKJEoMyAu8_JvZ9eY5b0YQbTB6sX1Gas-ZRtrMKXfxxpi7PEe8yeg$ 
>  
> [3] 
> https://urldefense.com/v3/__https://docs.kernel.org/process/coding-style.html?highlight=coding*style*placing-braces-and-spaces__;KyM!!CTRNKA9wMg0ARbw!jlYra3CQPXNsppOWspkAkRO2AfKJEoMyAu8_JvZ9eY5b0YQbTB6sX1Gas-ZRtrMKXfxxpi69jIOtSQ$ 
>  
> 
> 
> Thanks,
> SJ
> 
> >  	}
> >  	applied = reclaim_pages(&page_list);
> >  	cond_resched();
> > -- 
> > 2.18.0

Thanks for both of your suggestions, I will update the patch.