From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by kanga.kvack.org (Postfix) with ESMTP id 30D326B0254 for ; Fri, 11 Mar 2016 03:34:54 -0500 (EST) Received: by mail-pa0-f51.google.com with SMTP id tt10so90369148pab.3 for ; Fri, 11 Mar 2016 00:34:54 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id o63si12337521pfi.141.2016.03.11.00.34.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Mar 2016 00:34:53 -0800 (PST) Date: Fri, 11 Mar 2016 11:34:40 +0300 From: Vladimir Davydov Subject: Re: [PATCH] mm: memcontrol: reclaim when shrinking memory.high below usage Message-ID: <20160311083440.GI1946@esperanza> References: <1457643015-8828-1-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1457643015-8828-1-git-send-email-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Thu, Mar 10, 2016 at 03:50:13PM -0500, Johannes Weiner wrote: > When setting memory.high below usage, nothing happens until the next > charge comes along, and then it will only reclaim its own charge and > not the now potentially huge excess of the new memory.high. This can > cause groups to stay in excess of their memory.high indefinitely. > > To fix that, when shrinking memory.high, kick off a reclaim cycle that > goes after the delta. I agree that we should reclaim the high excess, but I don't think it's a good idea to do it synchronously. Currently, memory.low and memory.high knobs can be easily used by a single-threaded load manager implemented in userspace, because it doesn't need to care about potential stalls caused by writes to these files. After this change it might happen that a write to memory.high would take long, seconds perhaps, so in order to react quickly to changes in other cgroups, a load manager would have to spawn a thread per each write to memory.high, which would complicate its implementation significantly. Since, in contrast to memory.max, memory.high definition allows cgroup to breach it, I believe it would be better if we spawned an asynchronous reclaim work from the kernel on write to memory.high instead of doing this synchronously. I guess we could reuse mem_cgroup->high_work for that. Thanks, Vladimir -- 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