From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb0-f200.google.com (mail-yb0-f200.google.com [209.85.213.200]) by kanga.kvack.org (Postfix) with ESMTP id E31DD6B0003 for ; Thu, 5 Apr 2018 15:45:15 -0400 (EDT) Received: by mail-yb0-f200.google.com with SMTP id b7-v6so18179946ybn.14 for ; Thu, 05 Apr 2018 12:45:15 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id y138sor2828966ywg.378.2018.04.05.12.45.15 for (Google Transport Security); Thu, 05 Apr 2018 12:45:15 -0700 (PDT) Date: Thu, 5 Apr 2018 12:45:12 -0700 From: Tejun Heo Subject: Re: [PATCH] mm: memcg: make sure memory.events is uptodate when waking pollers Message-ID: <20180405194512.GD3126663@devbig577.frc2.facebook.com> References: <20180324160901.512135-1-tj@kernel.org> <20180324160901.512135-2-tj@kernel.org> <20180404140855.GA28966@cmpxchg.org> <20180404141850.GC28966@cmpxchg.org> <20180404143447.GJ6312@dhcp22.suse.cz> <20180404165829.GA3126663@devbig577.frc2.facebook.com> <20180405175507.GA24817@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180405175507.GA24817@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Michal Hocko , vdavydov.dev@gmail.com, guro@fb.com, riel@surriel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, cgroups@vger.kernel.org, linux-mm@kvack.org On Thu, Apr 05, 2018 at 01:55:16PM -0400, Johannes Weiner wrote: > From 4369ce161a9085aa408f2eca54f9de72909ee1b1 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner > Date: Thu, 5 Apr 2018 11:53:55 -0400 > Subject: [PATCH] mm: memcg: make sure memory.events is uptodate when waking > pollers > > a983b5ebee57 ("mm: memcontrol: fix excessive complexity in memory.stat > reporting") added per-cpu drift to all memory cgroup stats and events > shown in memory.stat and memory.events. > > For memory.stat this is acceptable. But memory.events issues file > notifications, and somebody polling the file for changes will be > confused when the counters in it are unchanged after a wakeup. > > Luckily, the events in memory.events - MEMCG_LOW, MEMCG_HIGH, > MEMCG_MAX, MEMCG_OOM - are sufficiently rare and high-level that we > don't need per-cpu buffering for them: MEMCG_HIGH and MEMCG_MAX would > be the most frequent, but they're counting invocations of reclaim, > which is a complex operation that touches many shared cachelines. > > This splits memory.events from the generic VM events and tracks them > in their own, unbuffered atomic counters. That's also cleaner, as it > eliminates the ugly enum nesting of VM and cgroup events. > > Fixes: a983b5ebee57 ("mm: memcontrol: fix excessive complexity in memory.stat reporting") > Reported-by: Tejun Heo > Signed-off-by: Johannes Weiner Yeah, that works. FWIW, Acked-by: Tejun Heo Thanks. -- tejun