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Subject: Re: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose
 refcount is one
To:     Muchun Song <songmuchun@bytedance.com>, mike.kravetz@oracle.com,
        akpm@linux-foundation.org
Cc:     hillf.zj@alibaba-inc.com, n-horiguchi@ah.jp.nec.com,
        ak@linux.intel.com, yongjun_wei@trendmicro.com.cn, mhocko@suse.cz,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20210104065843.5658-1-songmuchun@bytedance.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <d81664e1-bde0-4dcb-f602-6eb201ceada0@redhat.com>
Date:   Tue, 5 Jan 2021 17:58:16 +0100
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On 04.01.21 07:58, Muchun Song wrote:
> If the refcount is one when it is migrated, it means that the page
> was freed from under us. So we are done and do not need to migrate.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/migrate.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4385f2fb5d18..a6631c4eb6a6 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
>  		return -ENOSYS;
>  	}
>  
> +	if (page_count(hpage) == 1) {
> +		/* page was freed from under us. So we are done. */
> +		putback_active_hugepage(hpage);
> +		return MIGRATEPAGE_SUCCESS;
> +	}
> +
>  	new_hpage = get_new_page(hpage, private);
>  	if (!new_hpage)
>  		return -ENOMEM;
> 

This series seems to fix quite some important cases (thanks). Do we want
to cc stable some/all?

-- 
Thanks,

David / dhildenb