From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f181.google.com (mail-pd0-f181.google.com [209.85.192.181]) by kanga.kvack.org (Postfix) with ESMTP id F36DE6B0035 for ; Thu, 31 Jul 2014 21:37:45 -0400 (EDT) Received: by mail-pd0-f181.google.com with SMTP id g10so4510928pdj.26 for ; Thu, 31 Jul 2014 18:37:45 -0700 (PDT) Received: from heian.cn.fujitsu.com ([59.151.112.132]) by mx.google.com with ESMTP id bz3si3924269pdb.493.2014.07.31.18.37.44 for ; Thu, 31 Jul 2014 18:37:45 -0700 (PDT) Message-ID: <53DAEFB5.7060501@cn.fujitsu.com> Date: Fri, 1 Aug 2014 09:39:01 +0800 From: Lai Jiangshan MIME-Version: 1.0 Subject: Re: [PATCH] swap: remove the struct cpumask has_work References: <1406777421-12830-3-git-send-email-laijs@cn.fujitsu.com> <20140731115137.GA20244@dhcp22.suse.cz> <53DA6A2F.100@tilera.com> In-Reply-To: <53DA6A2F.100@tilera.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Chris Metcalf Cc: Michal Hocko , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Mel Gorman , Tejun Heo , Christoph Lameter , Frederic Weisbecker , Andrea Arcangeli , Rik van Riel , Jianyu Zhan , Johannes Weiner , Khalid Aziz , linux-mm@kvack.org, Gilad Ben-Yossef On 08/01/2014 12:09 AM, Chris Metcalf wrote: > On 7/31/2014 7:51 AM, Michal Hocko wrote: >> On Thu 31-07-14 11:30:19, Lai Jiangshan wrote: >>> It is suggested that cpumask_var_t and alloc_cpumask_var() should be used >>> instead of struct cpumask. But I don't want to add this complicity nor >>> leave this unwelcome "static struct cpumask has_work;", so I just remove >>> it and use flush_work() to perform on all online drain_work. flush_work() >>> performs very quickly on initialized but unused work item, thus we don't >>> need the struct cpumask has_work for performance. >> Why? Just because there is general recommendation for using >> cpumask_var_t rather than cpumask? >> >> In this particular case cpumask shouldn't matter much as it is static. >> Your code will work as well, but I do not see any strong reason to >> change it just to get rid of cpumask which is not on stack. > > The code uses for_each_cpu with a cpumask to avoid waking cpus that don't > need to do work. This is important for the nohz_full type functionality, > power efficiency, etc. So, nack for this change. > flush_work() on initialized but unused work item just disables irq and fetches work->data to test and restores irq and return. the struct cpumask has_work is just premature optimization. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org