linux-kernel - Re: [PATCH 4/6] mm/hwpoison: don't set migration type twice to avoid hold heavy contend zone->lock

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Date:	Thu, 22 Aug 2013 15:06:05 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Tony Luck <tony.luck@...el.com>, gong.chen@...ux.intel.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] mm/hwpoison: don't set migration type twice to avoid
 hold heavy contend zone->lock

On Thu, Aug 22, 2013 at 05:48:25PM +0800, Wanpeng Li wrote:
> Set pageblock migration type will hold zone->lock which is heavy contended 
> in system to avoid race. However, soft offline page will set pageblock 
> migration type twice during get page if the page is in used, not hugetlbfs 
> page and not on lru list. There is unnecessary to set the pageblock migration
> type and hold heavy contended zone->lock again if the first round get page 
> have already set the pageblock to right migration type.

Can we use get_pageblock_migratetype() outside zone->lock?

There are surely some users which call this function outside
zone->lock like free_hot_cold_pages(), __free_pages, etc.,
but I think that there's a race window where migratetype is
updated just after get_pageblock_migratetype() check.

> Signed-off-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> ---
>  mm/memory-failure.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 6bfd51e..3bfb45f 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1413,7 +1413,8 @@ static int __get_any_page(struct page *p, unsigned long pfn, int flags)
>  	 * was free. This flag should be kept set until the source page
>  	 * is freed and PG_hwpoison on it is set.
>  	 */
> -	set_migratetype_isolate(p, true);
> +	if (get_pageblock_migratetype(p) == MIGRATE_ISOLATE)

You meant '!=', right?

Thanks,
Naoya Horiguchi

> +		set_migratetype_isolate(p, true);
>  	/*
>  	 * When the target page is a free hugepage, just remove it
>  	 * from free hugepage list.
> -- 
> 1.8.1.2
>
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