Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755912AbcKKLMY (ORCPT ); Fri, 11 Nov 2016 06:12:24 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35597 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752813AbcKKLMW (ORCPT ); Fri, 11 Nov 2016 06:12:22 -0500 Date: Fri, 11 Nov 2016 14:12:19 +0300 From: "Kirill A. Shutemov" To: Dave Hansen , Pavel Emelyanov Cc: Naoya Horiguchi , linux-mm@kvack.org, "Kirill A. Shutemov" , Hugh Dickins , Andrew Morton , Andrea Arcangeli , Mel Gorman , Michal Hocko , Vlastimil Babka , Zi Yan , Balbir Singh , linux-kernel@vger.kernel.org, Naoya Horiguchi Subject: Re: [PATCH v2 01/12] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 6 Message-ID: <20161111111219.GD19382@node.shutemov.name> References: <1478561517-4317-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1478561517-4317-2-git-send-email-n-horiguchi@ah.jp.nec.com> <534caa72-c109-9716-15d2-5e80f4038f8d@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <534caa72-c109-9716-15d2-5e80f4038f8d@intel.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1257 Lines: 30 On Thu, Nov 10, 2016 at 03:29:51PM -0800, Dave Hansen wrote: > On 11/07/2016 03:31 PM, Naoya Horiguchi wrote: > > pmd_present() checks _PAGE_PSE along with _PAGE_PRESENT to avoid false negative > > return when it races with thp spilt (during which _PAGE_PRESENT is temporary > > cleared.) I don't think that dropping _PAGE_PSE check in pmd_present() works > > well because it can hurt optimization of tlb handling in thp split. > > In the current kernel, bit 6 is not used in non-present format because nonlinear > > file mapping is obsolete, so let's move _PAGE_SWP_SOFT_DIRTY to that bit. > > Bit 7 is used as reserved (always clear), so please don't use it for other > > purpose. > ... > > #ifdef CONFIG_MEM_SOFT_DIRTY > > -#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE > > +#define _PAGE_SWP_SOFT_DIRTY _PAGE_DIRTY > > #else > > #define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) > > #endif > > I'm not sure this works. Take a look at commit 00839ee3b29 and the > erratum it works around. I _think_ this means that a system affected by > the erratum might see an erroneous _PAGE_SWP_SOFT_DIRTY/_PAGE_DIRTY get > set in swap ptes. But, is it destructive in any way? What is the harm if we mark swap entry dirty by mistake? Pavel? -- Kirill A. Shutemov