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

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Date:   Sat, 9 Apr 2022 10:36:19 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Yang Shi <shy828301@...il.com>,
        David Hildenbrand <david@...hat.com>
CC:     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 2022/4/9 1:32, Yang Shi wrote:
> 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."

That's indeed what I want to say.

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

Many thanks for both of you! Will do it in v3.

> 
>>
>>>
>>> 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
>>
>>
> .
>