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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED,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 2C068C433E1 for ; Sun, 16 Aug 2020 03:48:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1230C2065C for ; Sun, 16 Aug 2020 03:48:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729691AbgHPDsO (ORCPT ); Sat, 15 Aug 2020 23:48:14 -0400 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:49280 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728950AbgHPDsO (ORCPT ); Sat, 15 Aug 2020 23:48:14 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04427;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0U5s0mT9_1597549686; Received: from aliy80.localdomain(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U5s0mT9_1597549686) by smtp.aliyun-inc.com(127.0.0.1); Sun, 16 Aug 2020 11:48:11 +0800 From: Alex Shi Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 2/2] mm/pageblock: remove false sharing in pageblock_flags Date: Sun, 16 Aug 2020 11:47:57 +0800 Message-Id: <1597549677-7480-2-git-send-email-alex.shi@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> References: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Current pageblock_flags is only 4 bits, so it has to share a char size in cmpxchg when get set, the false sharing cause perf drop. If we incrase the bits up to 8, false sharing would gone in cmpxchg. and the only cost is half char per pageblock, which is half char per 128MB on x86, 4 chars in 1 GB. Signed-off-by: Alex Shi Cc: Andrew Morton Cc: Hugh Dickins Cc: Alexander Duyck Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org --- include/linux/pageblock-flags.h | 2 +- mm/page_alloc.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h index d189441568eb..556fc2c0b392 100644 --- a/include/linux/pageblock-flags.h +++ b/include/linux/pageblock-flags.h @@ -25,7 +25,7 @@ enum pageblock_bits { * Assume the bits will always align on a word. If this assumption * changes then get/set pageblock needs updating. */ - NR_PAGEBLOCK_BITS + NR_PAGEBLOCK_BITS = 8 }; #ifdef CONFIG_HUGETLB_PAGE diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 142803d1f49b..01c3fb822732 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -521,7 +521,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, unsigned long bitidx, word_bitidx; unsigned char old_word, word; - BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4); + BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 8); BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); bitmap = get_pageblock_bitmap(page, pfn); -- 1.8.3.1