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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A90FC43334 for ; Fri, 8 Jul 2022 14:07:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238229AbiGHOHu (ORCPT ); Fri, 8 Jul 2022 10:07:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236628AbiGHOHs (ORCPT ); Fri, 8 Jul 2022 10:07:48 -0400 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DCF93313A8 for ; Fri, 8 Jul 2022 07:07:47 -0700 (PDT) Received: by mail-ej1-x62a.google.com with SMTP id h23so37850354ejj.12 for ; Fri, 08 Jul 2022 07:07:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=UmQMSw/Lo/aUgwdf6X3tLXsFA1/lan16IQ3/ce55QGc=; b=e//7/zevFojSgOmv1iUZPcR9RxpOxiTq/3m9/uN6nMSXeI3cXH4ixaWg5fpOBb1Xyq 2/6CsOMlmIQ90xk3ZqpS9GmPsMEN77fRzrXujYwyvsFbFyV+Yr6pt7yDy8oh4YLBJHuI J4kwdndVmwW26wL2r1fIHKQXzEUE7DZIyQAZGyj6Jt0fO9fs6YuDgnPOK9CNdckL5ovW 9ckRgnYGvYqeB3OyMnm6b6nYTos1wFBo2zRVCQH6TzwBZY1iiWIj/wS0HJu578+a/37m CBMaGj+SfkKAEihV4KGfQTD6lzxvioUDTGkr2PHCMSz63svr+8UiaWd4Huyh6CIUuIWQ Gt0g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=UmQMSw/Lo/aUgwdf6X3tLXsFA1/lan16IQ3/ce55QGc=; b=YYsjxGiXX5iPnui2qAzY6Sx19tDduizZwFLHCW0pFWGMlzjjiP9vGPt/U1EiqcxAI1 bJ/IKNWvxo8wpvbcLe7tLT0ad/Veu7lSEpBUQiSmwMJN2N882LIMayREpN7YSx0OLMBa Z8Hn/BwDVSvi2oGPslQzO6QSK8iI9yqmiddpU9BLmD66WAIyjhAbPWSqnDhBb1F7A/Rq sxi3RJP7nLY8r1jz61lHDCJz89DoWeZwIoAGMcKWcPnwF/JaQomwm1epU2WGhukj8uFm IX2xwaLDdmxk3laEbyIxRkmWE3CXDQ6DgSX+lvvfHuQNI28LS0lQ5E/LGIHYFlbPVkT1 uW9g== X-Gm-Message-State: AJIora8NXW7RZFR3+NiPndmewAPbMs3mhOM7/3BPAoq/sSAu/gUjjbgG fJ/AOl722b8T+79UNaAdh3FrwUQ6gZI= X-Google-Smtp-Source: AGRyM1t1DjCzfOwLiRgELsKcXKYuqKjMDw7UMRA/ZepHVRPjeRcW0Dz4HWw2KyJ1desnWjuhUEvOGw== X-Received: by 2002:a17:906:e16:b0:726:a026:27ff with SMTP id l22-20020a1709060e1600b00726a02627ffmr3646857eji.573.1657289266405; Fri, 08 Jul 2022 07:07:46 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id 1-20020a170906308100b007030c97ae62sm9533959ejv.191.2022.07.08.07.07.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Jul 2022 07:07:45 -0700 (PDT) From: Uros Bizjak To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Andrew Morton Subject: [PATCH] mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask Date: Fri, 8 Jul 2022 16:07:36 +0200 Message-Id: <20220708140736.8737-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use try_cmpxchg instead of cmpxchg in set_pfnblock_flags_mask. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). The main loop improves from: 1c5d: 48 89 c2 mov %rax,%rdx 1c60: 48 89 c1 mov %rax,%rcx 1c63: 48 21 fa and %rdi,%rdx 1c66: 4c 09 c2 or %r8,%rdx 1c69: f0 48 0f b1 16 lock cmpxchg %rdx,(%rsi) 1c6e: 48 39 c1 cmp %rax,%rcx 1c71: 75 ea jne 1c5d <...> to: 1c60: 48 89 ca mov %rcx,%rdx 1c63: 48 21 c2 and %rax,%rdx 1c66: 4c 09 c2 or %r8,%rdx 1c69: f0 48 0f b1 16 lock cmpxchg %rdx,(%rsi) 1c6e: 75 f0 jne 1c60 <...> Signed-off-by: Uros Bizjak Cc: Andrew Morton --- mm/page_alloc.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e008a3df0485..d415d5b539b7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -524,7 +524,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, { unsigned long *bitmap; unsigned long bitidx, word_bitidx; - unsigned long old_word, word; + unsigned long word; BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4); BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); @@ -540,12 +540,8 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, flags <<= bitidx; word = READ_ONCE(bitmap[word_bitidx]); - for (;;) { - old_word = cmpxchg(&bitmap[word_bitidx], word, (word & ~mask) | flags); - if (word == old_word) - break; - word = old_word; - } + do { + } while (!try_cmpxchg(&bitmap[word_bitidx], &word, (word & ~mask) | flags)); } void set_pageblock_migratetype(struct page *page, int migratetype) -- 2.35.3