Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161219AbbKFL26 (ORCPT ); Fri, 6 Nov 2015 06:28:58 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:47874 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031997AbbKFL24 (ORCPT ); Fri, 6 Nov 2015 06:28:56 -0500 To: cl@linux.com Cc: htejun@gmail.com, akpm@linux-foundation.org, mhocko@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, hannes@cmpxchg.org, mgorman@suse.de Subject: Re: [patch 3/3] vmstat: Create our own workqueue From: Tetsuo Handa References: <20151029022447.GB27115@mtj.duckdns.org> <20151029030822.GD27115@mtj.duckdns.org> <201510311143.BIH87000.tOSVFHOFJMLFOQ@I-love.SAKURA.ne.jp> In-Reply-To: Message-Id: <201511062028.DFE13506.MtVSOOFJLFOHQF@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Fri, 6 Nov 2015 20:28:52 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1642 Lines: 36 Christoph Lameter wrote: > On Sat, 31 Oct 2015, Tetsuo Handa wrote: > > > Then, you need to update below description (or drop it) because > > patch 3/3 alone will not guarantee that the counters are up to date. > > The vmstat system does not guarantee that the counters are up to date > always. The whole point is the deferral of updates for performance > reasons. They are updated *at some point* within stat_interval. That needs > to happen and that is what this patchset is fixing. So, if you refer to the blocking of the execution of vmstat updates, description for patch 3/3 sould be updated to something like below? ---------- Since __GFP_WAIT memory allocations do not call schedule() when there is nothing to reclaim, and workqueue does not kick remaining workqueue items unless in-flight workqueue item calls schedule(), __GFP_WAIT memory allocation requests by workqueue items can block vmstat_update work item forever. Since zone_reclaimable() decision depends on vmstat counters to be up to dated, a silent lockup occurs because a workqueue item doing a __GFP_WAIT memory allocation request continues using outdated vmstat counters. In order to fix this problem, we need to allocate a dedicated workqueue for vmstat. Note that this patch itself does not fix lockup problem. Tejun will develop a patch which detects lockup situation and kick remaining workqueue items. ---------- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/