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 06B06C636D3 for ; Mon, 6 Feb 2023 19:19:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229607AbjBFTTU (ORCPT ); Mon, 6 Feb 2023 14:19:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229573AbjBFTTS (ORCPT ); Mon, 6 Feb 2023 14:19:18 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E4C0B2D50 for ; Mon, 6 Feb 2023 11:19:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=OBskYcCmJm4DSmxJ+NjrmWZXF5UFVcrYYt7C0YtAI/g=; b=nM8n/bqCKnKqpg+9skte84LWNg 82gnXXwFMJvHhretSpzuVJerqX6Qyr1+2GYAz9VjjHL4PIIP8htf8QpCOxUAKEaUnQS5uFKz0LRyL mub5H9PrS4nur7ZIBhl8y5jksaj8TX+mBgvMJfj5AUcQbheOK0BgdGAcZ0K2s/s2BnPfooR28RRP5 hVvYSQzMHF6xcWi9Bs0x6yOStJ5f9035ihxbYXWyAJkg1SXSEFNL76Nl+WrCasnDtjOAJQiyeWab2 9nC7xfF9EEYVvVwrA8/KW0G36qXKMI0eCJBAzQ2UPMD4ivs4KmZOmg+sBkZF7xqrHo1F55/f/mziM V7Sd24Qw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pP718-00H1HJ-Qd; Mon, 06 Feb 2023 19:19:06 +0000 Date: Mon, 6 Feb 2023 19:19:06 +0000 From: Matthew Wilcox To: Marcelo Tosatti Cc: Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold Message-ID: References: <20230201195013.881721887@redhat.com> <20230201195104.460373427@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230201195104.460373427@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 01, 2023 at 04:50:16PM -0300, Marcelo Tosatti wrote: > In preparation to switch vmstat shepherd to flush > per-CPU counters remotely, use a cmpxchg loop > instead of a pair of read/write instructions. FYI, try_cmpxchg() is preferred to plain cmpxchg() these days. Apparently it generates better code on x86. > - v = pzstats->vm_stat_diff[i]; > - pzstats->vm_stat_diff[i] = 0; > + do { > + v = pzstats->vm_stat_diff[i]; > + } while (cmpxchg(&pzstats->vm_stat_diff[i], v, 0) != v); I think this would be: do { v = pzstats->vm_stat_diff[i]; } while (!try_cmpxchg(&pzstats->vm_stat_diff[i], v, 0));