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Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page
To:     Miaohe Lin <linmiaohe@huawei.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>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <e060283a-6295-9191-9b92-a3c183e9de02@redhat.com>
Date:   Mon, 6 Sep 2021 11:40:29 +0200
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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?

-- 
Thanks,

David / dhildenb