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Subject: Re: [PATCH 08/16] mm/page_alloc: add missing is_migrate_isolate()
 check in set_page_guard()
To:     Oscar Salvador <osalvador@suse.de>
CC:     <akpm@linux-foundation.org>, <david@redhat.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
References: <20220909092451.24883-1-linmiaohe@huawei.com>
 <20220909092451.24883-9-linmiaohe@huawei.com>
 <YyLTl8FvmcRuUYi9@localhost.localdomain>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <8a23c1b4-494e-1006-ee8c-e27a798d9f8f@huawei.com>
Date:   Thu, 15 Sep 2022 16:11:25 +0800
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On 2022/9/15 15:26, Oscar Salvador wrote:
> On Fri, Sep 09, 2022 at 05:24:43PM +0800, Miaohe Lin wrote:
>> In MIGRATE_ISOLATE case, zone freepage state shouldn't be modified as
>> caller will take care of it. Add missing is_migrate_isolate() here to
>> avoid possible unbalanced freepage state.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> 
> Ok, I gave it some thought and I guess it's safe to assume that this would happen if
> someone isolates the block, and then we face an MCE failure/soft-offline on a page
> within that block.
> 
> take_page_off_buddy
>  break_down_buddy_pages
>   set_page_guard
> 
> will trigger __mod_zone_freepage_state(), which already had been triggered back
> when the block was isolated.
> 
> I think the changelog could grow fatter to better explain the issue.

That will be really helpful. Will do it in v2.

> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

Many thanks for your suggestion and review.

Thanks,
Miaohe Lin

> 
>> ---
>>  mm/page_alloc.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index a35ef385d906..94baf33da865 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -873,7 +873,8 @@ static inline bool set_page_guard(struct zone *zone, struct page *page,
>>  	INIT_LIST_HEAD(&page->buddy_list);
>>  	set_page_private(page, order);
>>  	/* Guard pages are not available for any usage */
>> -	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
>> +	if (!is_migrate_isolate(migratetype))
>> +		__mod_zone_freepage_state(zone, -(1 << order), migratetype);
>>  
>>  	return true;
>>  }
>> -- 
>> 2.23.0
>>
>