From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752470AbaGYMSZ (ORCPT ); Fri, 25 Jul 2014 08:18:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:39579 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751966AbaGYMSY (ORCPT ); Fri, 25 Jul 2014 08:18:24 -0400 Date: Fri, 25 Jul 2014 13:18:15 +0100 From: Mel Gorman To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , David Rientjes , linux-kernel@vger.kernel.org, Minchan Kim , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel , Zhang Yanfei Subject: Re: [PATCH V4 01/15] mm, THP: don't hold mmap_sem in khugepaged when allocating THP Message-ID: <20140725121815.GV10819@suse.de> References: <1405518503-27687-1-git-send-email-vbabka@suse.cz> <1405518503-27687-2-git-send-email-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1405518503-27687-2-git-send-email-vbabka@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 16, 2014 at 03:48:09PM +0200, Vlastimil Babka wrote: > When allocating huge page for collapsing, khugepaged currently holds mmap_sem > for reading on the mm where collapsing occurs. Afterwards the read lock is > dropped before write lock is taken on the same mmap_sem. > > Holding mmap_sem during whole huge page allocation is therefore useless, the > vma needs to be rechecked after taking the write lock anyway. Furthemore, huge > page allocation might involve a rather long sync compaction, and thus block > any mmap_sem writers and i.e. affect workloads that perform frequent m(un)map > or mprotect oterations. > > This patch simply releases the read lock before allocating a huge page. It > also deletes an outdated comment that assumed vma must be stable, as it was > using alloc_hugepage_vma(). This is no longer true since commit 9f1b868a13 > ("mm: thp: khugepaged: add policy for finding target node"). > > Signed-off-by: Vlastimil Babka Acked-by: Mel Gorman -- Mel Gorman SUSE Labs