linux-kernel - Re: [PATCH 01/18] mm: numa: Serialise parallel get_user

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Date:	Mon, 09 Dec 2013 09:08:38 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Thorlton <athorlton@....com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/18] mm: numa: Serialise parallel get_user_page against
 THP migration

On 12/09/2013 02:08 AM, Mel Gorman wrote:
> Base pages are unmapped and flushed from cache and TLB during normal page
> migration and replaced with a migration entry that causes any parallel or
> gup to block until migration completes. THP does not unmap pages due to
> a lack of support for migration entries at a PMD level. This allows races
> with get_user_pages and get_user_pages_fast which commit 3f926ab94 ("mm:
> Close races between THP migration and PMD numa clearing") made worse by
> introducing a pmd_clear_flush().
> 
> This patch forces get_user_page (fast and normal) on a pmd_numa page to
> go through the slow get_user_page path where it will serialise against THP
> migration and properly account for the NUMA hinting fault. On the migration
> side the page table lock is taken for each PTE update.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Reviewed-by: Rik van Riel <riel@...hat.com>

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