linux-kernel - Re: [PATCH] mm: migrate: drop redundant anonymous statistics for file folios migration

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Message-ID: <6896a7ab-b6f6-4b2f-944a-c1c3f731bead@linux.alibaba.com>
Date: Thu, 5 Dec 2024 14:50:15 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, david@...hat.com,
 ying.huang@...ux.alibaba.com, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: drop redundant anonymous statistics for file
 folios migration



On 2024/12/5 14:33, Barry Song wrote:
> On Thu, Dec 5, 2024 at 7:06 PM Baolin Wang
> <baolin.wang@...ux.alibaba.com> wrote:
>>
>>
>>
>> On 2024/12/5 13:00, Barry Song wrote:
>>> On Thu, Dec 5, 2024 at 4:54 PM Baolin Wang
>>> <baolin.wang@...ux.alibaba.com> wrote:
>>>>
>>>> Commit 5d65c8d758f2 ("mm: count the number of anonymous THPs per size") adds
>>>> a new anonymous counter per THP size, however, when folio_mapping() is not NULL
>>>> during folio migration, it means this is not an anonymous folio, so remove the
>>>> redundant anonymous statistics in this case.
>>>
>>> why? Are you sure anon folios won't call __folio_migrate_mapping()?
>>> folio->mapping is PAGE_MAPPING_ANON for anon folios.
>>>
>>> static __always_inline bool folio_test_anon(const struct folio *folio)
>>> {
>>>           return ((unsigned long)folio->mapping & PAGE_MAPPING_ANON) != 0;
>>> }
>>
>> Ah, sorry for noise. This just caught my eyes when reading the code, and
>> I did not think about it deeply before sending a quick patch. Thanks to
>> Barry and Ying for the reminder.
> 
> No worries. I recall encountering a negative count during the development of
> the original patch and eventually realizing it was due to forgetting
> to increment
> the migrated anon folios. Your patch seems to reintroduce the bug I encountered
> back then :-)

Right. I was blind and need a cup of coffee:)