Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751581AbcKIFAH convert rfc822-to-8bit (ORCPT ); Wed, 9 Nov 2016 00:00:07 -0500 Received: from TYO202.gate.nec.co.jp ([210.143.35.52]:52203 "EHLO tyo202.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750766AbcKIFAF (ORCPT ); Wed, 9 Nov 2016 00:00:05 -0500 From: Naoya Horiguchi To: Balbir Singh CC: "linux-mm@kvack.org" , "Kirill A. Shutemov" , Hugh Dickins , "Andrew Morton" , Dave Hansen , Andrea Arcangeli , Mel Gorman , Michal Hocko , "Vlastimil Babka" , Pavel Emelyanov , Zi Yan , "linux-kernel@vger.kernel.org" , Naoya Horiguchi Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp Thread-Topic: [PATCH v2 00/12] mm: page migration enhancement for thp Thread-Index: AQHSOVAK6wj8CPCOIkad3aMzBQ1vK6DPWWoAgAApLAA= Date: Wed, 9 Nov 2016 04:59:27 +0000 Message-ID: <20161109045926.GB7770@hori1.linux.bs1.fc.nec.co.jp> References: <1478561517-4317-1-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.128.101.2] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <4FD04AB28C784F478330A49F406C589E@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: 3385 Lines: 98 On Wed, Nov 09, 2016 at 01:32:04PM +1100, Balbir Singh wrote: > On 08/11/16 10:31, Naoya Horiguchi wrote: > > Hi everyone, > > > > I've updated thp migration patches for v4.9-rc2-mmotm-2016-10-27-18-27 > > with feedbacks for ver.1. > > > > General description (no change since ver.1) > > =========================================== > > > > This patchset enhances page migration functionality to handle thp migration > > for various page migration's callers: > > - mbind(2) > > - move_pages(2) > > - migrate_pages(2) > > - cgroup/cpuset migration > > - memory hotremove > > - soft offline > > > > The main benefit is that we can avoid unnecessary thp splits, which helps us > > avoid performance decrease when your applications handles NUMA optimization on > > their own. > > > > The implementation is similar to that of normal page migration, the key point > > is that we modify a pmd to a pmd migration entry in swap-entry like format. > > > > Changes / Notes > > =============== > > > > - pmd_present() in x86 checks _PAGE_PRESENT, _PAGE_PROTNONE and _PAGE_PSE > > bits together, which makes implementing thp migration a bit hard because > > _PAGE_PSE bit is currently used by soft-dirty in swap-entry format. > > I was advised to dropping _PAGE_PSE in pmd_present(), but I don't think > > of the justification, so I keep it in this version. Instead, my approach > > is to move _PAGE_SWP_SOFT_DIRTY to bit 6 (unused) and reserve bit 7 for > > pmd non-present cases. > > Thanks, IIRC > > pmd_present = _PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PSE > > AutoNUMA balancing would change it to > > pmd_present = _PAGE_PROTNONE | _PAGE_PSE > > and PMD_SWP_SOFT_DIRTY would make it > > pmd_present = _PAGE_PSE > > What you seem to be suggesting in your comment is that > > pmd_present should be _PAGE_PRESENT | _PAGE_PROTNONE This (no _PAGE_PSE) was a possibile solution, and as I described I gave up this solution, because I noticed that what I actually wanted was that pmd_present() certainly returns false during thp migration and that's done by moving _PAGE_SWP_SOFT_DIRTY. So pmd_present = _PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PSE is still correct in this patchset. > > Isn't that good enough? > > For THP migration I guess we use > > _PAGE_PRESENT | _PAGE_PROTNONE | is_migration_entry(pmd) Though I might misread your notations, I hope that the following code seems describe itself well. static inline int is_pmd_migration_entry(pmd_t pmd) { return !pmd_present(pmd) && is_migration_entry(pmd_to_swp_entry(pmd)); } Thanks, Naoya Horiguchi > > > > > > - this patchset still covers only x86_64. Zi Yan posted a patch for ppc64 > > and I think it's favorably received so that's fine. But there's unsolved > > minor suggestion by Aneesh, so I don't include it in this set, expecting > > that it will be updated/reposted. > > > > - pte-mapped thp and doubly-mapped thp were not supported in ver.1, but > > this version should work for such kinds of thp. > > > > - thp page cache is not tested yet, and it's at the head of my todo list > > for future version. > > > > Any comments or advices are welcomed. > > Balbir Singh >