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=-11.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, 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 B634FC433E6 for ; Sun, 30 Aug 2020 10:14:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7A271207DA for ; Sun, 30 Aug 2020 10:14:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7A271207DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C4CDF6B0006; Sun, 30 Aug 2020 06:14:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BFD506B0007; Sun, 30 Aug 2020 06:14:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B14DA6B0008; Sun, 30 Aug 2020 06:14:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0219.hostedemail.com [216.40.44.219]) by kanga.kvack.org (Postfix) with ESMTP id A4ED36B0006 for ; Sun, 30 Aug 2020 06:14:41 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 64F504435 for ; Sun, 30 Aug 2020 10:14:41 +0000 (UTC) X-FDA: 77206825962.09.badge78_580905f27086 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id 2F448180AD801 for ; Sun, 30 Aug 2020 10:14:41 +0000 (UTC) X-HE-Tag: badge78_580905f27086 X-Filterd-Recvd-Size: 4714 Received: from out30-57.freemail.mail.aliyun.com (out30-57.freemail.mail.aliyun.com [115.124.30.57]) by imf07.hostedemail.com (Postfix) with ESMTP for ; Sun, 30 Aug 2020 10:14:39 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04392;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0U7FapVA_1598782473; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U7FapVA_1598782473) by smtp.aliyun-inc.com(127.0.0.1); Sun, 30 Aug 2020 18:14:34 +0800 Subject: Re: [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags To: Anshuman Khandual , Matthew Wilcox , David Hildenbrand Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> From: Alex Shi Message-ID: <01c846d4-2fe4-eeef-6c79-e71fda1f9a39@linux.alibaba.com> Date: Sun, 30 Aug 2020 18:14:33 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> Content-Type: text/plain; charset=utf-8 X-Rspamd-Queue-Id: 2F448180AD801 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: =E5=9C=A8 2020/8/19 =E4=B8=8B=E5=8D=883:55, Anshuman Khandual =E5=86=99=E9= =81=93: >=20 >=20 > On 08/19/2020 11:17 AM, Alex Shi wrote: >> pageblock_flags is used as long, since every pageblock_flags is just 4 >> bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flag= s, >> 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. >=20 > Do you have numbers demonstrating claimed performance improvement > after this change ? >=20 the performance data show in another email. LKP reported the arm6 has a bug on this patchset, since it has no cmpxchg= b solution, so maybe let's fallback to cmpxchg on it. >From db3d97ba8cc5e206b440bd40a92ef6955ad86bc0 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Tue, 18 Aug 2020 15:51:18 +0800 Subject: [PATCH v2 3/3] armv6: fix armv6 build issue Arm v6 can not simulate cmpxchg1 func, so we have to use cmpxchg4 on it. arm-linux-gnueabi-ld: mm/page_alloc.o: in function `set_pfnblock_flags= _mask': (.text+0x32b4): undefined reference to `__bad_cmpxchg' arm-linux-gnueabi-ld: (.text+0x32e0): undefined reference to `__bad_cm= pxchg' arm-linux-gnueabi-ld: drivers/net/ethernet/aquantia/atlantic/hw_atl/hw= _atl_b0.o: in function `hw_atl_b0_get_mac_temp': hw_atl_b0.c:(.text+0x30fc): undefined reference to `__bad_udelay' Reported-by: kernel test robot Signed-off-by: Alex Shi Cc: Andrew Morton Cc: Baolin Wang Cc: Russell King Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org --- mm/page_alloc.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7da09d66233b..c09146a8946c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -517,7 +517,11 @@ void set_pfnblock_flags_mask(struct page *page, unsi= gned long flags, { unsigned char *bitmap; unsigned long bitidx, byte_bitidx; +#ifdef CONFIG_CPU_V6 + unsigned long old_byte, byte; +#else unsigned char old_byte, byte; +#endif =20 BUILD_BUG_ON(NR_PAGEBLOCK_BITS !=3D BITS_PER_BYTE); BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); @@ -532,9 +536,18 @@ void set_pfnblock_flags_mask(struct page *page, unsi= gned long flags, mask <<=3D bitidx; flags <<=3D bitidx; =20 +#ifdef CONFIG_CPU_V6 + byte =3D (unsigned long)READ_ONCE(bitmap[byte_bitidx]); +#else byte =3D READ_ONCE(bitmap[byte_bitidx]); +#endif for (;;) { +#ifdef CONFIG_CPU_V6 + /* arm v6 has no cmpxchgb function, so still false sharing long word *= / + old_byte =3D cmpxchg((unsigned long*)&bitmap[byte_bitidx], byte, (byte= & ~mask) | flags); +#else old_byte =3D cmpxchg(&bitmap[byte_bitidx], byte, (byte & ~mask) | flag= s); +#endif if (byte =3D=3D old_byte) break; byte =3D old_byte; --=20 1.8.3.1