From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-f71.google.com (mail-yw1-f71.google.com [209.85.161.71]) by kanga.kvack.org (Postfix) with ESMTP id 70BA98E0001 for ; Fri, 11 Jan 2019 15:59:55 -0500 (EST) Received: by mail-yw1-f71.google.com with SMTP id x64so8458481ywc.6 for ; Fri, 11 Jan 2019 12:59:55 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v4sor10669047ywd.1.2019.01.11.12.59.49 for (Google Transport Security); Fri, 11 Jan 2019 12:59:49 -0800 (PST) Date: Fri, 11 Jan 2019 15:59:48 -0500 From: Johannes Weiner Subject: Re: [PATCH v3] memcg: schedule high reclaim for remote memcgs on high_work Message-ID: <20190111205948.GA4591@cmpxchg.org> References: <20190110174432.82064-1-shakeelb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190110174432.82064-1-shakeelb@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt Cc: Michal Hocko , Andrew Morton , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Shakeel, On Thu, Jan 10, 2019 at 09:44:32AM -0800, Shakeel Butt wrote: > If a memcg is over high limit, memory reclaim is scheduled to run on > return-to-userland. However it is assumed that the memcg is the current > process's memcg. With remote memcg charging for kmem or swapping in a > page charged to remote memcg, current process can trigger reclaim on > remote memcg. So, schduling reclaim on return-to-userland for remote > memcgs will ignore the high reclaim altogether. So, record the memcg > needing high reclaim and trigger high reclaim for that memcg on > return-to-userland. However if the memcg is already recorded for high > reclaim and the recorded memcg is not the descendant of the the memcg > needing high reclaim, punt the high reclaim to the work queue. The idea behind remote charging is that the thread allocating the memory is not responsible for that memory, but a different cgroup is. Why would the same thread then have to work off any high excess this could produce in that unrelated group? Say you have a inotify/dnotify listener that is restricted in its memory use - now everybody sending notification events from outside that listener's group would get throttled on a cgroup over which it has no control. That sounds like a recipe for priority inversions. It seems to me we should only do reclaim-on-return when current is in the ill-behaved cgroup, and punt everything else - interrupts and remote charges - to the workqueue.