From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754220AbaJBPU7 (ORCPT ); Thu, 2 Oct 2014 11:20:59 -0400 Received: from mta-out1.inet.fi ([62.71.2.234]:33070 "EHLO kirsi1.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753591AbaJBPU6 (ORCPT ); Thu, 2 Oct 2014 11:20:58 -0400 Date: Thu, 2 Oct 2014 18:18:07 +0300 From: "Kirill A. Shutemov" To: Mel Gorman Cc: Dave Jones , Linus Torvalds , Hugh Dickins , Al Viro , Rik van Riel , Ingo Molnar , Peter Zijlstra , Aneesh Kumar , Michel Lespinasse , Kirill A Shutemov , Linux Kernel Subject: Re: [PATCH 4/4] mm: numa: Do not mark PTEs pte_numa when splitting huge pages Message-ID: <20141002151807.GA13668@node.dhcp.inet.fi> References: <1412256558-9995-1-git-send-email-mgorman@suse.de> <1412256558-9995-5-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412256558-9995-5-git-send-email-mgorman@suse.de> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 02, 2014 at 02:29:18PM +0100, Mel Gorman wrote: > This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the > NUMA type from the pmd to the pte"). If a huge page is being split due > a protection change and the tail will be in a PROT_NONE vma then NUMA > hinting PTEs are temporarily created in the protected VMA. > > VM_RW|VM_PROTNONE > |-----------------| > ^ > split here > > In the specific case above, it should get fixed up by change_pte_range() > but there is a window of opportunity for weirdness to happen. Similarly, > if a huge page is shrunk and split during a protection update but before > pmd_numa is cleared then a pte_numa can be left behind. > > Instead of adding complexity trying to deal with the case, this patch > will not mark PTEs NUMA when splitting a huge page. NUMA hinting faults > will not be triggered which is marginal in comparison to the complexity > in dealing with the corner cases during THP split. > > Signed-off-by: Mel Gorman I think it deserves a comment to avoid re-introducing NUMA type transferring. Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov