From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f43.google.com (mail-ee0-f43.google.com [74.125.83.43]) by kanga.kvack.org (Postfix) with ESMTP id 20B306B0031 for ; Tue, 15 Apr 2014 10:44:30 -0400 (EDT) Received: by mail-ee0-f43.google.com with SMTP id e53so7840739eek.2 for ; Tue, 15 Apr 2014 07:44:29 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 45si25876064eeh.63.2014.04.15.07.44.27 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 15 Apr 2014 07:44:28 -0700 (PDT) Date: Tue, 15 Apr 2014 15:44:24 +0100 From: Mel Gorman Subject: Re: [PATCH 4/5] mm: use paravirt friendly ops for NUMA hinting ptes Message-ID: <20140415144423.GV7292@suse.de> References: <1396962570-18762-1-git-send-email-mgorman@suse.de> <1396962570-18762-5-git-send-email-mgorman@suse.de> <534D09AC.7020704@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <534D09AC.7020704@citrix.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Vrabel Cc: Linux-X86 , Linus Torvalds , Cyrill Gorcunov , Peter Anvin , Ingo Molnar , Steven Noonan , Rik van Riel , Andrew Morton , Peter Zijlstra , Andrea Arcangeli , Dave Hansen , Srikar Dronamraju , Linux-MM , LKML On Tue, Apr 15, 2014 at 11:27:56AM +0100, David Vrabel wrote: > On 08/04/14 14:09, Mel Gorman wrote: > > David Vrabel identified a regression when using automatic NUMA balancing > > under Xen whereby page table entries were getting corrupted due to the > > use of native PTE operations. Quoting him > > > > Xen PV guest page tables require that their entries use machine > > addresses if the preset bit (_PAGE_PRESENT) is set, and (for > > successful migration) non-present PTEs must use pseudo-physical > > addresses. This is because on migration MFNs in present PTEs are > > translated to PFNs (canonicalised) so they may be translated back > > to the new MFN in the destination domain (uncanonicalised). > > > > pte_mknonnuma(), pmd_mknonnuma(), pte_mknuma() and pmd_mknuma() > > set and clear the _PAGE_PRESENT bit using pte_set_flags(), > > pte_clear_flags(), etc. > > > > In a Xen PV guest, these functions must translate MFNs to PFNs > > when clearing _PAGE_PRESENT and translate PFNs to MFNs when setting > > _PAGE_PRESENT. > > > > His suggested fix converted p[te|md]_[set|clear]_flags to using > > paravirt-friendly ops but this is overkill. He suggested an alternative of > > using p[te|md]_modify in the NUMA page table operations but this is does > > more work than necessary and would require looking up a VMA for protections. > > > > This patch modifies the NUMA page table operations to use paravirt friendly > > operations to set/clear the flags of interest. Unfortunately this will take > > a performance hit when updating the PTEs on CONFIG_PARAVIRT but I do not > > see a way around it that does not break Xen. > > We're getting more reports of users hitting this regression with distro > provided kernels. Irrespective of the rest of this series, can we get > at least this applied and tagged for stable, please? > > http://lists.xenproject.org/archives/html/xen-devel/2014-04/msg01905.html > The resending of the series got delayed until today. Fengguang Wu hit problems testing the series and I ran into a number of similarly shaped problems that took time to resolve. I sent out a v4 of the series with this patch at the front and a note on the leader saying it should be picked up for stable regardless of what happens with the patches 2 and 3. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org