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=-8.2 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_SANE_1 autolearn=ham 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 5E83EC0044D for ; Mon, 16 Mar 2020 17:49:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3571420663 for ; Mon, 16 Mar 2020 17:49:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732243AbgCPRtf (ORCPT ); Mon, 16 Mar 2020 13:49:35 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:45363 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732228AbgCPRtf (ORCPT ); Mon, 16 Mar 2020 13:49:35 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R271e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0TsoNvPO_1584380967; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TsoNvPO_1584380967) by smtp.aliyun-inc.com(127.0.0.1); Tue, 17 Mar 2020 01:49:29 +0800 Subject: Re: [PATCH 2/2] mm: swap: use smp_mb__after_atomic() to order LRU bit set To: Vlastimil Babka , shakeelb@google.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1584124476-76534-1-git-send-email-yang.shi@linux.alibaba.com> <1584124476-76534-2-git-send-email-yang.shi@linux.alibaba.com> <3c13c484-8fbf-3c3a-fbe1-a40434869e55@suse.cz> From: Yang Shi Message-ID: <52877743-bb43-f928-2995-92607272dbb8@linux.alibaba.com> Date: Mon, 16 Mar 2020 10:49:26 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <3c13c484-8fbf-3c3a-fbe1-a40434869e55@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/16/20 10:40 AM, Vlastimil Babka wrote: > On 3/13/20 7:34 PM, Yang Shi wrote: >> Memory barrier is needed after setting LRU bit, but smp_mb() is too >> strong. Some architectures, i.e. x86, imply memory barrier with atomic >> operations, so replacing it with smp_mb__after_atomic() sounds better, >> which is nop on strong ordered machines, and full memory barriers on >> others. With this change the vm-calability cases would perform better >> on x86, I saw total 6% improvement with this patch and previous inline >> fix. >> >> The test data (lru-file-readtwice throughput) against v5.6-rc4: >> mainline w/ inline fix w/ both (adding this) >> 150MB 154MB 159MB >> >> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs") >> Cc: Shakeel Butt >> Cc: Vlastimil Babka >> Signed-off-by: Yang Shi > According to my understanding of Documentation/memory_barriers.txt this would be > correct (but it might not say much :) This is my understanding too. > > Acked-by: Vlastimil Babka > > But i have some suggestions... > >> --- >> mm/swap.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/mm/swap.c b/mm/swap.c >> index cf39d24..118bac4 100644 >> --- a/mm/swap.c >> +++ b/mm/swap.c >> @@ -945,20 +945,20 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec, >> * #0: __pagevec_lru_add_fn #1: clear_page_mlock >> * >> * SetPageLRU() TestClearPageMlocked() >> - * smp_mb() // explicit ordering // above provides strict >> + * MB() // explicit ordering // above provides strict > Why MB()? That would be the first appareance of 'MB()' in the whole tree. I > think it's fine keeping smp_mb()... I would like to use a more general name, maybe just use "memory barrier"? > >> * // ordering >> * PageMlocked() PageLRU() >> * >> * >> * if '#1' does not observe setting of PG_lru by '#0' and fails >> * isolation, the explicit barrier will make sure that page_evictable >> - * check will put the page in correct LRU. Without smp_mb(), SetPageLRU >> + * check will put the page in correct LRU. Without MB(), SetPageLRU > ... same here ... > >> * can be reordered after PageMlocked check and can make '#1' to fail >> * the isolation of the page whose Mlocked bit is cleared (#0 is also >> * looking at the same page) and the evictable page will be stranded >> * in an unevictable LRU. > Only here I would note that SetPageLRU() is an atomic bitop so we can use the > __after_atomic() variant. And I would move the actual SetPageLRU() call from > above the comment here right before the barrier. Sure. Thanks. > >> */ >> - smp_mb(); >> + smp_mb__after_atomic(); > Thanks. > >> >> if (page_evictable(page)) { >> lru = page_lru(page); >>