From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vc0-f180.google.com (mail-vc0-f180.google.com [209.85.220.180]) by kanga.kvack.org (Postfix) with ESMTP id BA99A6B0031 for ; Tue, 1 Apr 2014 14:43:12 -0400 (EDT) Received: by mail-vc0-f180.google.com with SMTP id lf12so10058239vcb.39 for ; Tue, 01 Apr 2014 11:43:12 -0700 (PDT) Received: from mail-vc0-x229.google.com (mail-vc0-x229.google.com [2607:f8b0:400c:c03::229]) by mx.google.com with ESMTPS id cm9si3864380vcb.46.2014.04.01.11.43.11 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 01 Apr 2014 11:43:11 -0700 (PDT) Received: by mail-vc0-f169.google.com with SMTP id ik5so10389117vcb.14 for ; Tue, 01 Apr 2014 11:43:11 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <533B0301.3010507@citrix.com> References: <1395425902-29817-1-git-send-email-david.vrabel@citrix.com> <1395425902-29817-3-git-send-email-david.vrabel@citrix.com> <533016CB.4090807@citrix.com> <20140331122625.GR25087@suse.de> <533B0301.3010507@citrix.com> Date: Tue, 1 Apr 2014 11:43:11 -0700 Message-ID: Subject: Re: [PATCH 2/2] x86: use pv-ops in {pte,pmd}_{set,clear}_flags() From: Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: David Vrabel Cc: Mel Gorman , Steven Noonan , Rik van Riel , Andrew Morton , Ingo Molnar , Peter Zijlstra , linux-mm On Tue, Apr 1, 2014 at 11:18 AM, David Vrabel wrote: > > I don't think it's sufficient to avoid collisions with bits used only > with P=0. The original value of this bit must be retained when the > _PAGE_NUMA bit is set/cleared. > > Bit 7 is PAT[2] and whilst Linux currently sets up the PAT such that > PAT[2] is a 'don't care', there has been talk up adjusting the PAT to > include more types. So I'm not sure it's a good idea to use bit 7. > > What's wrong with using e.g., bit 62? And not supporting this NUMA > rebalancing feature on 32-bit non-PAE builds? Sounds good to me, but it's not available in 32-bit PAE. The high bits are all reserved, afaik. But you'd have to be insane to care about NUMA balancing on 32-bit, even with PAE. So restricting it to x86-64 and using the high bits (I think bits 52-62 are all available to SW) sounds fine to me. Same goes for soft-dirty. I think it's fine if we say that you won't have soft-dirty with a 32-bit kernel. Even with PAE. Linus -- 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