Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965127AbcKKBJb convert rfc822-to-8bit (ORCPT ); Thu, 10 Nov 2016 20:09:31 -0500 Received: from TYO201.gate.nec.co.jp ([210.143.35.51]:60462 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964868AbcKKBJa (ORCPT ); Thu, 10 Nov 2016 20:09:30 -0500 From: Naoya Horiguchi To: Dave Hansen CC: "linux-mm@kvack.org" , "Kirill A. Shutemov" , Hugh Dickins , "Andrew Morton" , Andrea Arcangeli , Mel Gorman , Michal Hocko , Vlastimil Babka , Pavel Emelyanov , "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 Thread-Topic: [PATCH v2 01/12] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 6 Thread-Index: AQHSOU8ruh1UI3IyjUmElP3izhZM26DSSyyAgAAblQA= Date: Fri, 11 Nov 2016 01:08:36 +0000 Message-ID: <20161111010834.GA28679@hori1.linux.bs1.fc.nec.co.jp> 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> In-Reply-To: <534caa72-c109-9716-15d2-5e80f4038f8d@intel.com> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.7] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <4519D00B843E514D95B1F7709ACA6AA8@gisp.nec.co.jp> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1533 Lines: 33 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 file mapping is obsolete, so let's move _PAGE_SWP_SOFT_DIRTY to that bit.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. > > There are much worse things that can happen, but I don't think bits 5 > (Accessed) and 6 (Dirty) are good choices since they're affected by the > erratum. Thank you for the information. According to 00839ee3b29, some bits which are safe from the errata are reclaimed, so assigning one of such bits for _PAGE_SWP_SOFT_DIRTY seems to work. And I'll update the description. Thanks, Naoya Horiguchi