linux-kernel - Re: [PATCH 3/3] mm/memory_hotplug: make HWPoisoned dirty swapcache pages unmovable

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Message-ID: <20210823082646.GB1452382@hori.linux.bs1.fc.nec.co.jp>
Date:   Mon, 23 Aug 2021 08:26:47 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "cgoldswo@...eaurora.org" <cgoldswo@...eaurora.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm/memory_hotplug: make HWPoisoned dirty swapcache
 pages unmovable

On Sat, Aug 21, 2021 at 05:42:46PM +0800, Miaohe Lin wrote:
> HWPoisoned dirty swapcache pages are kept for killing owner processes.
> We should not offline these pages or do_swap_page() would access the
> offline pages and lead to bad ending.
> 

Thank you for the report.  I'm not yet sure of the whole picture of this
issue.  do_swap_page() is expected to return with fault VM_FAULT_HWPOISON
when called via the access to the error page, so I wonder why this doesn't
work for your situation.  And what is the "bad ending" in the description?

I feel that aborting memory hotremove due to a hwpoisoned dirty swapcache
might be too hard, so I'd like to find another solution if we have.
# You may separate this patch from former two to make them merged to
# mainline soon.

Thanks,
Naoya Horiguchi

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/memory_hotplug.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9fd0be32a281..0488eed3327c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1664,6 +1664,12 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>  		 */
>  		if (PageOffline(page) && page_count(page))
>  			return -EBUSY;
> +		/*
> +		 * HWPoisoned dirty swapcache pages are definitely unmovable
> +		 * because they are kept for killing owner processes.
> +		 */
> +		if (PageHWPoison(page) && PageSwapCache(page))
> +			return -EBUSY;