Re: [PATCH 1/5] mm/vmscan: put the redirtied MADV_FREE pages back to anonymous LRU list

From: Michal Hocko <mhocko@suse.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, vbabka@suse.cz,
	axboe@kernel.dk, iamjoonsoo.kim@lge.com, alexs@kernel.org,
	apopple@nvidia.com, willy@infradead.org, minchan@kernel.org,
	david@redhat.com, shli@fb.com, hillf.zj@alibaba-inc.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] mm/vmscan: put the redirtied MADV_FREE pages back to anonymous LRU list
Date: Mon, 12 Jul 2021 09:22:03 +0200	[thread overview]
Message-ID: <YOvtmy9ggJA4KUIQ@dhcp22.suse.cz> (raw)
In-Reply-To: <20210710100329.49174-2-linmiaohe@huawei.com>

On Sat 10-07-21 18:03:25, Miaohe Lin wrote:
> If the MADV_FREE pages are redirtied before they could be reclaimed, put
> the pages back to anonymous LRU list by setting SwapBacked flag and the
> pages will be reclaimed in normal swapout way. Otherwise MADV_FREE pages
> won't be reclaimed as expected.

Could you describe problem which you are trying to address? What does it
mean that pages won't be reclaimed as expected?

Also why is SetPageSwapBacked in shrink_page_list insufficient?

> Fixes: 802a3a92ad7a ("mm: reclaim MADV_FREE pages")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/vmscan.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a7602f71ec04..6483fe0e2065 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1628,6 +1628,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
>  			if (!page_ref_freeze(page, 1))
>  				goto keep_locked;
>  			if (PageDirty(page)) {
> +				SetPageSwapBacked(page);
>  				page_ref_unfreeze(page, 1);
>  				goto keep_locked;
>  			}
> -- 
> 2.23.0

-- 
Michal Hocko
SUSE Labs