From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757189AbbCSSJS (ORCPT ); Thu, 19 Mar 2015 14:09:18 -0400 Received: from mail-ig0-f170.google.com ([209.85.213.170]:33576 "EHLO mail-ig0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752624AbbCSSJQ (ORCPT ); Thu, 19 Mar 2015 14:09:16 -0400 MIME-Version: 1.0 In-Reply-To: <20150319141022.GD3087@suse.de> References: <20150312131045.GE3406@suse.de> <20150312184925.GH3406@suse.de> <20150317070655.GB10105@dastard> <20150317205104.GA28621@dastard> <20150317220840.GC28621@dastard> <20150319141022.GD3087@suse.de> Date: Thu, 19 Mar 2015 11:09:15 -0700 X-Google-Sender-Auth: xhsHYEYAHyjgvIQ7cZJl-Zaji3Y Message-ID: Subject: Re: [PATCH 4/4] mm: numa: Slow PTE scan rate if migration failures occur From: Linus Torvalds To: Mel Gorman Cc: Dave Chinner , Ingo Molnar , Andrew Morton , Aneesh Kumar , Linux Kernel Mailing List , Linux-MM , xfs@oss.sgi.com, ppc-dev Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 19, 2015 at 7:10 AM, Mel Gorman wrote: > - if (!pmd_dirty(pmd)) > + /* See similar comment in do_numa_page for explanation */ > + if (!(vma->vm_flags & VM_WRITE)) Yeah, that would certainly be a whole lot more obvious than all the "if this particular pte/pmd looks like X" tests. So that, together with scanning rate improvements (this *does* seem to be somewhat chaotic, so it's quite possible that the current scanning rate thing is just fairly unstable) is likely the right thing. I'd just like to _understand_ why that write/dirty bit makes such a difference. I thought I understood what was going on, and was happy, and then Dave come with his crazy numbers. Damn you Dave, and damn your numbers and "facts" and stuff. Sometimes I much prefer ignorant bliss. Linus