linux-kernel - Re: [PATCH v5 1/4] mm,hwpoison: drain pcplists before bailing out for non-buddy zero-refcount page

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Date:   Wed, 25 Nov 2020 17:26:47 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Oscar Salvador <osalvador@...e.de>, n-horiguchi@...jp.nec.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@....com>
Subject: Re: [PATCH v5 1/4] mm,hwpoison: drain pcplists before bailing out for
 non-buddy zero-refcount page

On 10/13/20 4:44 PM, Oscar Salvador wrote:
> A page with 0-refcount and !PageBuddy could perfectly be a pcppage.
> Currently, we bail out with an error if we encounter such a page, meaning
> that we do not handle pcppages neither from hard-offline nor from
> soft-offline path.
> 
> Fix this by draining pcplists whenever we find this kind of page and retry
> the check again.  It might be that pcplists have been spilled into the
> buddy allocator and so we can handle it.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Naoya Horiguchi <naoya.horiguchi@....com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/memory-failure.c | 24 ++++++++++++++++++++++--
>   1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index c0bb186bba62..e2f12410c594 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -946,13 +946,13 @@ static int page_action(struct page_state *ps, struct page *p,
>   }
>   
>   /**
> - * get_hwpoison_page() - Get refcount for memory error handling:
> + * __get_hwpoison_page() - Get refcount for memory error handling:
>    * @page:	raw error page (hit by memory error)
>    *
>    * Return: return 0 if failed to grab the refcount, otherwise true (some
>    * non-zero value.)
>    */
> -static int get_hwpoison_page(struct page *page)
> +static int __get_hwpoison_page(struct page *page)
>   {
>   	struct page *head = compound_head(page);
>   
> @@ -982,6 +982,26 @@ static int get_hwpoison_page(struct page *page)
>   	return 0;
>   }
>   
> +static int get_hwpoison_page(struct page *p)
> +{
> +	int ret;
> +	bool drained = false;
> +
> +retry:
> +	ret = __get_hwpoison_page(p);
> +	if (!ret && !is_free_buddy_page(p) && !page_count(p) && !drained) {
> +		/*
> +		 * The page might be in a pcplist, so try to drain those
> +		 * and see if we are lucky.
> +		 */
> +		drain_all_pages(page_zone(p));
> +		drained = true;
> +		goto retry;
> +	}
> +
> +	return ret;
> +}
> +
>   /*
>    * Do all that is necessary to remove user space mappings. Unmap
>    * the pages and send SIGBUS to the processes if the data was dirty.
>