From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id 3BE016B0038 for ; Wed, 9 Nov 2016 16:29:17 -0500 (EST) Received: by mail-pa0-f69.google.com with SMTP id r13so80880355pag.1 for ; Wed, 09 Nov 2016 13:29:17 -0800 (PST) Received: from mail-pf0-x242.google.com (mail-pf0-x242.google.com. [2607:f8b0:400e:c00::242]) by mx.google.com with ESMTPS id j130si1227746pgc.172.2016.11.09.13.29.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Nov 2016 13:29:16 -0800 (PST) Received: by mail-pf0-x242.google.com with SMTP id y68so1509509pfb.1 for ; Wed, 09 Nov 2016 13:29:16 -0800 (PST) Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp References: <1478561517-4317-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20161109045926.GB7770@hori1.linux.bs1.fc.nec.co.jp> From: Balbir Singh Message-ID: Date: Thu, 10 Nov 2016 08:28:54 +1100 MIME-Version: 1.0 In-Reply-To: <20161109045926.GB7770@hori1.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi 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 On 09/11/16 15:59, Naoya Horiguchi wrote: > 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. > Thanks, I was wondering if there is any advantage or you felt its safer not to change pmd_present(). >> >> 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, yes my notation is not the best. Balbir Singh. -- 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