From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60FFAC17447 for ; Mon, 11 Nov 2019 22:09:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 372AA2173B for ; Mon, 11 Nov 2019 22:09:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726976AbfKKWJg (ORCPT ); Mon, 11 Nov 2019 17:09:36 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:48721 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726845AbfKKWJf (ORCPT ); Mon, 11 Nov 2019 17:09:35 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R831e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07417;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0Thpy97A_1573510165; Received: from e19h19392.et15sqa.tbsite.net(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0Thpy97A_1573510165) by smtp.aliyun-inc.com(127.0.0.1); Tue, 12 Nov 2019 06:09:31 +0800 From: Yang Shi To: mhocko@suse.com, mgorman@techsingularity.net, vbabka@suse.cz, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: migrate: handle freed page at the first place Date: Tue, 12 Nov 2019 06:09:25 +0800 Message-Id: <1573510165-113395-1-git-send-email-yang.shi@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When doing migration if the freed page is met, we just return without migrating it since it is pointless to migrate a freed page. But, the current code did two things before handling freed page: 1. Return -ENOMEM if the page is THP and THP migration is not supported. 2. Allocate target page unconditionally. Both makes not too much sense. If we handle freed page at the first place we don't have to worry about allocating/freeing target page and split THP at all. For example (worst case) if we are trying to migrate a freed THP without THP migration supported, the migrate_pages() would just split the THP then retry to migrate base pages one by one by pointless allocating and freeing pages, this is just waste of time. I didn't run into any actual problem with the current code (or I may just not notice it yet), it was found by visual inspection. Cc: Michal Hocko Cc: Mel Gorman Cc: Vlastimil Babka Signed-off-by: Yang Shi --- mm/migrate.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index 4fe45d1..ef96997 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1170,13 +1170,6 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, int rc = MIGRATEPAGE_SUCCESS; struct page *newpage; - if (!thp_migration_supported() && PageTransHuge(page)) - return -ENOMEM; - - newpage = get_new_page(page, private); - if (!newpage) - return -ENOMEM; - if (page_count(page) == 1) { /* page was freed from under us. So we are done. */ ClearPageActive(page); @@ -1187,13 +1180,16 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page, __ClearPageIsolated(page); unlock_page(page); } - if (put_new_page) - put_new_page(newpage, private); - else - put_page(newpage); goto out; } + if (!thp_migration_supported() && PageTransHuge(page)) + return -ENOMEM; + + newpage = get_new_page(page, private); + if (!newpage) + return -ENOMEM; + rc = __unmap_and_move(page, newpage, force, mode); if (rc == MIGRATEPAGE_SUCCESS) set_page_owner_migrate_reason(newpage, reason); -- 1.8.3.1