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=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 CDFCFC433DF for ; Sun, 16 Aug 2020 03:48:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC9CF2065C for ; Sun, 16 Aug 2020 03:48:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730008AbgHPDsK (ORCPT ); Sat, 15 Aug 2020 23:48:10 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:48824 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728950AbgHPDsK (ORCPT ); Sat, 15 Aug 2020 23:48:10 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R281e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07488;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 11:48:07 +0800 From: Alex Shi Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Date: Sun, 16 Aug 2020 11:47:56 +0800 Message-Id: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 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 pageblock_flags is used as long, since every pageblock_flags is just 4 bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags, that flag setting has to sync in cmpxchg with 7 or 15 other pageblock flags. It would cause long waiting for sync. If we could change the pageblock_flags variable as char, we could use char size cmpxchg, which just sync up with 2 pageblock flags. it could relief much false sharing in cmpxchg. Signed-off-by: Alex Shi Cc: Andrew Morton Cc: Hugh Dickins Cc: Alexander Duyck Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org --- include/linux/mmzone.h | 6 +++--- include/linux/pageblock-flags.h | 2 +- mm/page_alloc.c | 24 +++++++++++++----------- 3 files changed, 17 insertions(+), 15 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 0ed520954843..c92d6d24527d 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -438,7 +438,7 @@ struct zone { * Flags for a pageblock_nr_pages block. See pageblock-flags.h. * In SPARSEMEM, this map is stored in struct mem_section */ - unsigned long *pageblock_flags; + unsigned char *pageblock_flags; #endif /* CONFIG_SPARSEMEM */ /* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */ @@ -1159,7 +1159,7 @@ struct mem_section_usage { DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION); #endif /* See declaration of similar field in struct zone */ - unsigned long pageblock_flags[0]; + unsigned char pageblock_flags[0]; }; void subsection_map_init(unsigned long pfn, unsigned long nr_pages); @@ -1212,7 +1212,7 @@ struct mem_section { extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]; #endif -static inline unsigned long *section_to_usemap(struct mem_section *ms) +static inline unsigned char *section_to_usemap(struct mem_section *ms) { return ms->usage->pageblock_flags; } diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h index fff52ad370c1..d189441568eb 100644 --- a/include/linux/pageblock-flags.h +++ b/include/linux/pageblock-flags.h @@ -54,7 +54,7 @@ enum pageblock_bits { /* Forward declaration */ struct page; -unsigned long get_pfnblock_flags_mask(struct page *page, +unsigned char get_pfnblock_flags_mask(struct page *page, unsigned long pfn, unsigned long mask); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 66d45e9cc358..142803d1f49b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -447,7 +447,7 @@ static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn) #endif /* Return a pointer to the bitmap storing bits affecting a block of pages */ -static inline unsigned long *get_pageblock_bitmap(struct page *page, +static inline unsigned char *get_pageblock_bitmap(struct page *page, unsigned long pfn) { #ifdef CONFIG_SPARSEMEM @@ -467,6 +467,8 @@ static inline int pfn_to_bitidx(struct page *page, unsigned long pfn) return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS; } +#define BITS_PER_CHAR 8 + /** * get_pfnblock_flags_mask - Return the requested group of flags for the pageblock_nr_pages block of pages * @page: The page within the block of interest @@ -476,24 +478,24 @@ static inline int pfn_to_bitidx(struct page *page, unsigned long pfn) * Return: pageblock_bits flags */ static __always_inline -unsigned long __get_pfnblock_flags_mask(struct page *page, +unsigned char __get_pfnblock_flags_mask(struct page *page, unsigned long pfn, unsigned long mask) { - unsigned long *bitmap; + unsigned char *bitmap; unsigned long bitidx, word_bitidx; - unsigned long word; + unsigned char word; bitmap = get_pageblock_bitmap(page, pfn); bitidx = pfn_to_bitidx(page, pfn); - word_bitidx = bitidx / BITS_PER_LONG; - bitidx &= (BITS_PER_LONG-1); + word_bitidx = bitidx / BITS_PER_CHAR; + bitidx &= (BITS_PER_CHAR-1); word = bitmap[word_bitidx]; return (word >> bitidx) & mask; } -unsigned long get_pfnblock_flags_mask(struct page *page, unsigned long pfn, +unsigned char get_pfnblock_flags_mask(struct page *page, unsigned long pfn, unsigned long mask) { return __get_pfnblock_flags_mask(page, pfn, mask); @@ -515,17 +517,17 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, unsigned long pfn, unsigned long mask) { - unsigned long *bitmap; + unsigned char *bitmap; unsigned long bitidx, word_bitidx; - unsigned long old_word, word; + unsigned char old_word, word; BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4); BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); bitmap = get_pageblock_bitmap(page, pfn); bitidx = pfn_to_bitidx(page, pfn); - word_bitidx = bitidx / BITS_PER_LONG; - bitidx &= (BITS_PER_LONG-1); + word_bitidx = bitidx / BITS_PER_CHAR; + bitidx &= (BITS_PER_CHAR-1); VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); -- 1.8.3.1