linux-kernel - Re: [v2 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind

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Message-ID: <0cbc99f6-76a9-7357-efa7-a2d551b3cd12@suse.cz>
Date:   Tue, 16 Jul 2019 14:07:18 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...nel.org,
        mgorman@...hsingularity.net, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages
 mapped correctly in mbind

On 6/22/19 2:20 AM, Yang Shi wrote:
> @@ -969,10 +975,21 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
>  /*
>   * page migration, thp tail pages can be passed.
>   */
> -static void migrate_page_add(struct page *page, struct list_head *pagelist,
> +static int migrate_page_add(struct page *page, struct list_head *pagelist,
>  				unsigned long flags)
>  {
>  	struct page *head = compound_head(page);
> +
> +	/*
> +	 * Non-movable page may reach here.  And, there may be
> +	 * temporaty off LRU pages or non-LRU movable pages.
> +	 * Treat them as unmovable pages since they can't be
> +	 * isolated, so they can't be moved at the moment.  It
> +	 * should return -EIO for this case too.
> +	 */
> +	if (!PageLRU(head) && (flags & MPOL_MF_STRICT))
> +		return -EIO;
> +

Hm but !PageLRU() is not the only way why queueing for migration can
fail, as can be seen from the rest of the function. Shouldn't all cases
be reported?

>  	/*
>  	 * Avoid migrating a page that is shared with others.
>  	 */
> @@ -984,6 +1001,8 @@ static void migrate_page_add(struct page *page, struct list_head *pagelist,
>  				hpage_nr_pages(head));
>  		}
>  	}
> +
> +	return 0;
>  }
>  
>  /* page allocation callback for NUMA node migration */
> @@ -1186,9 +1205,10 @@ static struct page *new_page(struct page *page, unsigned long start)
>  }
>  #else
>  
> -static void migrate_page_add(struct page *page, struct list_head *pagelist,
> +static int migrate_page_add(struct page *page, struct list_head *pagelist,
>  				unsigned long flags)
>  {
> +	return -EIO;
>  }
>  
>  int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
>