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From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] mm: migrate: Move the page count validation to the proper place
Date: Fri, 6 Aug 2021 11:07:18 +0800	[thread overview]
Message-ID: <a02346d7-1a79-eb92-cb1f-033e6b58fa3f@linux.alibaba.com> (raw)
In-Reply-To: <YQwBD55FZyoY+C5D@casper.infradead.org>

Hi Matthew,

> On Thu, Aug 05, 2021 at 11:05:56PM +0800, Baolin Wang wrote:
>> We've got the expected count for anonymous page or file page by
>> expected_page_refs() at the beginning of migrate_page_move_mapping(),
>> thus we should move the page count validation a little forward to
>> reduce duplicated code.
> 
> Please add an explanation to the changelog for why it's safe to pull
> this out from under the i_pages lock.

Sure. In folio_migrate_mapping(), we are sure that the migration page 
was isolated from lru list and locked, so I think there are no race to 
get the page count without i_pages lock. Please correct me if I missed 
something else. Thanks.

> 
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>>   mm/migrate.c | 10 ++++------
>>   1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 239b238..5559571 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -386,11 +386,10 @@ int folio_migrate_mapping(struct address_space *mapping,
>>   	int expected_count = expected_page_refs(mapping, &folio->page) + extra_count;
>>   	long nr = folio_nr_pages(folio);
>>   
>> -	if (!mapping) {
>> -		/* Anonymous page without mapping */
>> -		if (folio_ref_count(folio) != expected_count)
>> -			return -EAGAIN;
>> +	if (folio_ref_count(folio) != expected_count)
>> +		return -EAGAIN;
>>   
>> +	if (!mapping) {
>>   		/* No turning back from here */
>>   		newfolio->index = folio->index;
>>   		newfolio->mapping = folio->mapping;
>> @@ -404,8 +403,7 @@ int folio_migrate_mapping(struct address_space *mapping,
>>   	newzone = folio_zone(newfolio);
>>   
>>   	xas_lock_irq(&xas);
>> -	if (folio_ref_count(folio) != expected_count ||
>> -	    xas_load(&xas) != folio) {
>> +	if (xas_load(&xas) != folio) {
>>   		xas_unlock_irq(&xas);
>>   		return -EAGAIN;
>>   	}
>> -- 
>> 1.8.3.1
>>
>>

  reply	other threads:[~2021-08-06  3:06 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 15:05 [PATCH 0/5] Some cleanup for page migration Baolin Wang
2021-08-05 15:05 ` [PATCH 1/5] mm: migrate: Move the page count validation to the proper place Baolin Wang
2021-08-05 15:17   ` Matthew Wilcox
2021-08-06  3:07     ` Baolin Wang [this message]
2021-08-07  2:02       ` Matthew Wilcox
2021-08-08  2:55         ` Baolin Wang
2021-08-08 10:26           ` Matthew Wilcox
2021-08-08 15:13             ` Baolin Wang
2021-08-08 16:01               ` Matthew Wilcox
2021-08-09  4:19                 ` Baolin Wang
2021-08-05 15:05 ` [PATCH 2/5] mm: migrate: Introduce a local variable to get the number of pages Baolin Wang
2021-08-05 17:42   ` Yang Shi
2021-08-05 15:05 ` [PATCH 3/5] mm: migrate: Fix the incorrect function name in comments Baolin Wang
2021-08-05 17:26   ` Yang Shi
2021-08-09 13:59   ` Alistair Popple
2021-08-05 15:05 ` [PATCH 4/5] mm: migrate: Change to use bool type for 'page_was_mapped' Baolin Wang
2021-08-05 17:34   ` Yang Shi
2021-08-05 15:06 ` [PATCH 5/5] mm: migrate: Remove redundant goto labels Baolin Wang
2021-08-05 19:54   ` Yang Shi
2021-08-06  3:20     ` Baolin Wang
2021-08-06 17:17       ` Yang Shi
2021-08-08  2:56         ` Baolin Wang

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