From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755285AbbAZSfF (ORCPT ); Mon, 26 Jan 2015 13:35:05 -0500 Received: from resqmta-ch2-07v.sys.comcast.net ([69.252.207.39]:32817 "EHLO resqmta-ch2-07v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752596AbbAZSfB (ORCPT ); Mon, 26 Jan 2015 13:35:01 -0500 Date: Mon, 26 Jan 2015 12:35:00 -0600 (CST) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Michal Hocko cc: Vinayak Menon , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, hannes@cmpxchg.org, vdavydov@parallels.com, mgorman@suse.de, minchan@kernel.org Subject: Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated In-Reply-To: <20150126174606.GD22681@dhcp22.suse.cz> Message-ID: References: <1421235419-30736-1-git-send-email-vinmenon@codeaurora.org> <20150114165036.GI4706@dhcp22.suse.cz> <54B7F7C4.2070105@codeaurora.org> <20150116154922.GB4650@dhcp22.suse.cz> <54BA7D3A.40100@codeaurora.org> <54BC879C.90505@codeaurora.org> <20150121143920.GD23700@dhcp22.suse.cz> <20150126174606.GD22681@dhcp22.suse.cz> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 Jan 2015, Michal Hocko wrote: > > Please do not run the vmstat_updates concurrently. They update shared > > cachelines and therefore can cause bouncing cachelines if run concurrently > > on multiple cpus. > > Would you preffer to call smp_call_function_single on each CPU > which needs an update? That would make vmstat_shepherd slower but that > is not a big deal, is it? Run it from the timer interrupt as usual from a work request? Those are staggered. > Anyway I am wondering whether the cache line bouncing between > vmstat_update instances is a big deal in the real life. Updating shared > counters whould bounce with many CPUs but this is an operation which is > not done often. Also all the CPUs would have update the same counters > all the time and I am not sure this happens that often. Do you have a > load where this would be measurable? Concurrent page faults update lots of counters concurrently. But will those trigger the smp_call_function?