linux-kernel - Re: [PATCH 1/3] mm/memory-failure.c: avoid false-postive PageSwapCache test

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Date:   Fri, 8 Apr 2022 10:32:33 -0700
From:   Yang Shi <shy828301@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Mike Kravetz <mike.kravetz@...cle.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm/memory-failure.c: avoid false-postive
 PageSwapCache test

On Fri, Apr 8, 2022 at 1:52 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 07.04.22 15:03, Miaohe Lin wrote:
> > PageSwapCache is only reliable when PageAnon is true because PG_swapcache
> > serves as PG_owner_priv_1 which can be used by fs if it's pagecache page.
> > So we should test PageAnon to distinguish pagecache page from swapcache
> > page to avoid false-postive PageSwapCache test.
>
> Well, that's not quite correct. Just because a page is PageAnon()
> doesn't mean that it's in the swapache. It means that it might be in the
> swapcache but cannot be in the pagecache.
>
> Maybe you wanted to say
>
> "So we should test PageAnon() to distinguish pagecache pages from
> anonymous pages."

Yeah, I agree. The patch looks fine to me with David's comment addressed.

>
> >
> > Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> > ---
> >  mm/memory-failure.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index ef402b490663..2e97302d62e4 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -2262,7 +2262,7 @@ static int __soft_offline_page(struct page *page)
> >               return 0;
> >       }
> >
> > -     if (!PageHuge(page) && PageLRU(page) && !PageSwapCache(page))
> > +     if (!PageHuge(page) && PageLRU(page) && !PageAnon(page))
> >               /*
> >                * Try to invalidate first. This should work for
> >                * non dirty unmapped page cache pages.
>
>
> --
> Thanks,
>
> David / dhildenb
>
>