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Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page
To:     David Hildenbrand <david@redhat.com>, <akpm@linux-foundation.org>
CC:     <vbabka@suse.cz>, <iamjoonsoo.kim@lge.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
References: <20210904091839.20270-1-linmiaohe@huawei.com>
 <e060283a-6295-9191-9b92-a3c183e9de02@redhat.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <b533742e-e82a-a721-9a24-4087688dd812@huawei.com>
Date:   Mon, 6 Sep 2021 19:32:30 +0800
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On 2021/9/6 17:40, David Hildenbrand wrote:
> On 04.09.21 11:18, Miaohe Lin wrote:
>> If __isolate_free_page() failed, due to zone watermark check, the page is
>> still on the free list. But this page will be put back to free list again
>> via __putback_isolated_page() now. This may trigger page->flags checks in
>> __free_one_page() if PageReported is set. Or we will corrupt the free list
>> because list_add() will be called for pages already on another list.
>>
>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>   mm/page_isolation.c | 6 ++----
>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 9bb562d5d194..7d70d772525c 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>>               buddy_pfn = __find_buddy_pfn(pfn, order);
>>               buddy = page + (buddy_pfn - pfn);
>>   -            if (!is_migrate_isolate_page(buddy)) {
>> -                __isolate_free_page(page, order);
>> -                isolated_page = true;
>> -            }
>> +            if (!is_migrate_isolate_page(buddy))
>> +                isolated_page = !!__isolate_free_page(page, order);
>>           }
>>       }
>>  
> 
> Shouldn't we much rather force to ignore watermarks here and make sure __isolate_free_page() never fails?

It seems it is not easy to force to ignore watermarks here. And it's not a problem
if __isolate_free_page() fails because we can do move_freepages_block() anyway.
What do you think? Many thanks.

>