From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id C6A686B0003 for ; Fri, 6 Apr 2018 08:03:10 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id n7so672518wrb.0 for ; Fri, 06 Apr 2018 05:03:10 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 54si7713742wry.283.2018.04.06.05.03.04 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 06 Apr 2018 05:03:04 -0700 (PDT) Date: Fri, 6 Apr 2018 14:03:02 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: memcg: make sure memory.events is uptodate when waking pollers Message-ID: <20180406120302.GL8286@dhcp22.suse.cz> 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: Tejun Heo , 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 05-04-18 13:55:16, 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. I agree with the patch I am just worried about the naming a bit. It is quite confusing TBH. events should be vm_events and memory_events should be limit_events or something like that. > Fixes: a983b5ebee57 ("mm: memcontrol: fix excessive complexity in memory.stat reporting") > Reported-by: Tejun Heo > Signed-off-by: Johannes Weiner Anyway Acked-by: Michal Hocko -- Michal Hocko SUSE Labs