From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754633AbdGSPBk (ORCPT ); Wed, 19 Jul 2017 11:01:40 -0400 Received: from mail-dm3nam03on0111.outbound.protection.outlook.com ([104.47.41.111]:15799 "EHLO NAM03-DM3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754016AbdGSPBi (ORCPT ); Wed, 19 Jul 2017 11:01:38 -0400 Authentication-Results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=cs.rutgers.edu; From: "Zi Yan" To: "Michal Hocko" Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kirill.shutemov@linux.intel.com, minchan@kernel.org, vbabka@suse.cz, mgorman@techsingularity.net, khandual@linux.vnet.ibm.com, dnellans@nvidia.com, dave.hansen@intel.com, n-horiguchi@ah.jp.nec.com Subject: Re: [PATCH v9 06/10] mm: thp: check pmd migration entry in common path Date: Wed, 19 Jul 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X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR14MB1649 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 3156 and 4880). --=_MailMate_B7607DC4-C4BD-4CC7-9C63-FB670B57C6D1_= Content-Type: text/plain On 19 Jul 2017, at 4:02, Michal Hocko wrote: > On Mon 17-07-17 15:39:51, Zi Yan wrote: >> From: Zi Yan >> >> If one of callers of page migration starts to handle thp, >> memory management code start to see pmd migration entry, so we need >> to prepare for it before enabling. This patch changes various code >> point which checks the status of given pmds in order to prevent race >> between thp migration and the pmd-related works. > > I am sorry to nitpick on the changelog but the patch is scary large and > it would deserve much better description. What are those "various code > point" and how do you "prevent race". How can we double check that none > of them were missed? Thanks for pointing this out. Let me know if the following new description looks good to you: When THP migration is being used, memory management code needs to handle pmd migration entries properly. This patch uses !pmd_present() or is_swap_pmd() (depending on whether pmd_none() needs separate code or not) to check pmd migration entries at the places where a pmd entry is present. Since pmd-related code uses split_huge_page(), split_huge_pmd(), pmd_trans_huge(), pmd_trans_unstable(), or pmd_none_or_trans_huge_or_clear_bad(), this patch: 1. adds pmd migration entry split code in split_huge_pmd(), 2. takes care of pmd migration entries whenever pmd_trans_huge() is present, 3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware. Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable() is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change them. Until this commit, a pmd entry should be: 1. pointing to a pte page, 2. is_swap_pmd(), 3. pmd_trans_huge(), 4. pmd_devmap(), or 5. pmd_none(). -- Best Regards Yan Zi --=_MailMate_B7607DC4-C4BD-4CC7-9C63-FB670B57C6D1_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQEcBAEBCgAGBQJZb3ROAAoJEEGLLxGcTqbMnM0IAIJk5fInIsfn5Ix/cfwDR1kS qt6scndZCaMoR+rEIRk8fcX4pwyXnWIW4LH1xl9w/+p6iYfWaCxellSeE5OHgiRL HGe3IJXfpTWOQfd8lT+qJbWWvNAOv7O12yBiF6IBu+kI3gI/syPAPjdHVmFTXM0a ds3IMwuc4d347SqKCbEbEndOSExa87IE6pcMKMtqvUxike3p1PJHdl0kIcki+iEV w2MhyAtvXJviZ+FKYsqGGvh8GgbND+HgC0d9+52QZ5hdoTUXyupQ9pPFk03eM6mw 1iT8JdLI670sSGUQ6Fj45Jl9ljDxzrM8UUJMZrEj5MCLzZ07fxWikbS3NFsBkGE= =mylc -----END PGP SIGNATURE----- --=_MailMate_B7607DC4-C4BD-4CC7-9C63-FB670B57C6D1_=--