Re: [PATCH 2/2] mm: page_isolation: fix zone_freepage accounting

[Weijie Yang]

On Thu, Nov 6, 2014 at 4:49 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> On Thu, Nov 06, 2014 at 04:09:08PM +0800, Weijie Yang wrote:
>> If race between isolatation and allocation happens, we could need to move
>> some freepages to MIGRATE_ISOLATE in __test_page_isolated_in_pageblock().
>> The current code ignores the zone_freepage accounting after the move,
>> which cause the zone NR_FREE_PAGES and NR_FREE_CMA_PAGES statistics incorrect.
>>
>> This patch fixes this rare issue.
>
> Hello,
>
> After "fix freepage count problems in memory isolation" merged, this race
> should not happen. I have to remove it in that patchset, but, I
> forgot to remove it. Please remove this race handling code completely and
> tag with stable. If we don't remove it, there is errornous situation
> because get_freepage_migratetype() could return invalid migratetype
> although the page is on the correct buddy list. So, we regard
> no race situation as race one.

Thanks for your remind, I will read your patch.

> Thanks.
>
>>
>> Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
>> ---
>>  mm/page_isolation.c |    5 ++++-
>>  1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 3ddc8b3..15b51de 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -193,12 +193,15 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
>>                        * is MIGRATE_ISOLATE. Catch it and move the page into
>>                        * MIGRATE_ISOLATE list.
>>                        */
>> -                     if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) {
>> +                     int migratetype = get_freepage_migratetype(page);
>> +                     if (migratetype != MIGRATE_ISOLATE) {
>>                               struct page *end_page;
>>
>>                               end_page = page + (1 << page_order(page)) - 1;
>>                               move_freepages(page_zone(page), page, end_page,
>>                                               MIGRATE_ISOLATE);
>> +                             __mod_zone_freepage_state(zone,
>> +                                     -(1 << page_order(page)), migratetype);
>>                       }
>>                       pfn += 1 << page_order(page);
>>               }
>> --
>> 1.7.0.4
>>
>>
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