From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760953AbZE1IzU (ORCPT ); Thu, 28 May 2009 04:55:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756316AbZE1IzI (ORCPT ); Thu, 28 May 2009 04:55:08 -0400 Received: from gir.skynet.ie ([193.1.99.77]:40420 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752578AbZE1IzG (ORCPT ); Thu, 28 May 2009 04:55:06 -0400 Date: Thu, 28 May 2009 09:55:04 +0100 From: Mel Gorman To: Ingo Molnar Cc: Andrew Morton , stable@kernel.org, Linux Memory Management List , Linux Kernel Mailing List , Hugh Dickins , Lee Schermerhorn , KOSAKI Motohiro , starlight@binnacle.cx, Eric B Munson , Adam Litke , Andy Whitcroft , wli@movementarian.org Subject: Re: [PATCH 1/2] x86: Ignore VM_LOCKED when determining if hugetlb-backed page tables can be shared or not Message-ID: <20090528085503.GB10334@csn.ul.ie> References: <1243422749-6256-1-git-send-email-mel@csn.ul.ie> <1243422749-6256-2-git-send-email-mel@csn.ul.ie> <20090527231803.GA30002@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090527231803.GA30002@elte.hu> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 28, 2009 at 01:18:03AM +0200, Ingo Molnar wrote: > > * Mel Gorman wrote: > > > On x86 and x86-64, it is possible that page tables are shared > > beween shared mappings backed by hugetlbfs. As part of this, > > page_table_shareable() checks a pair of vma->vm_flags and they > > must match if they are to be shared. All VMA flags are taken into > > account, including VM_LOCKED. > > > > The problem is that VM_LOCKED is cleared on fork(). When a process > > with a shared memory segment forks() to exec() a helper, there > > will be shared VMAs with different flags. The impact is that the > > shared segment is sometimes considered shareable and other times > > not, depending on what process is checking. > > > > What happens is that the segment page tables are being shared but > > the count is inaccurate depending on the ordering of events. As > > the page tables are freed with put_page(), bad pmd's are found > > when some of the children exit. The hugepage counters also get > > corrupted and the Total and Free count will no longer match even > > when all the hugepage-backed regions are freed. This requires a > > reboot of the machine to "fix". > > > > This patch addresses the problem by comparing all flags except > > VM_LOCKED when deciding if pagetables should be shared or not for > > hugetlbfs-backed mapping. > > > > Signed-off-by: Mel Gorman > > Acked-by: Hugh Dickins > > --- > > arch/x86/mm/hugetlbpage.c | 6 +++++- > > 1 files changed, 5 insertions(+), 1 deletions(-) > > i suspect it would be best to do this due -mm, due to the (larger) > mm/hugetlb.c cross section, right? > I'm happy with that approach. Almost all hugetlbfs-related patches have gone through -mm to date AFAIK even when they have been arch specific like this. Thanks -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab