From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id CA99A8E0002 for ; Thu, 3 Jan 2019 14:23:42 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id c53so34383909edc.9 for ; Thu, 03 Jan 2019 11:23:42 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g25si426116edv.186.2019.01.03.11.23.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Jan 2019 11:23:41 -0800 (PST) Date: Thu, 3 Jan 2019 20:23:39 +0100 From: Michal Hocko Subject: Re: [RFC PATCH 0/3] mm: memcontrol: delayed force empty Message-ID: <20190103192339.GA31793@dhcp22.suse.cz> References: <1546459533-36247-1-git-send-email-yang.shi@linux.alibaba.com> <20190103101215.GH31793@dhcp22.suse.cz> <20190103181329.GW31793@dhcp22.suse.cz> <6f43e926-3bb5-20d1-2e39-1d30bf7ad375@linux.alibaba.com> <20190103185333.GX31793@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 03-01-19 11:10:00, Yang Shi wrote: > > > On 1/3/19 10:53 AM, Michal Hocko wrote: > > On Thu 03-01-19 10:40:54, Yang Shi wrote: > > > > > > On 1/3/19 10:13 AM, Michal Hocko wrote: [...] > > > > Is there any reason for your scripts to be strictly sequential here? In > > > > other words why cannot you offload those expensive operations to a > > > > detached context in _userspace_? > > > I would say it has not to be strictly sequential. The above script is just > > > an example to illustrate the pattern. But, sometimes it may hit such pattern > > > due to the complicated cluster scheduling and container scheduling in the > > > production environment, for example the creation process might be scheduled > > > to the same CPU which is doing force_empty. I have to say I don't know too > > > much about the internals of the container scheduling. > > In that case I do not see a strong reason to implement the offloding > > into the kernel. It is an additional code and semantic to maintain. > > Yes, it does introduce some additional code and semantic, but IMHO, it is > quite simple and very straight forward, isn't it? Just utilize the existing > css offline worker. And, that a couple of lines of code do improve some > throughput issues for some real usecases. I do not really care it is few LOC. It is more important that it is conflating force_empty into offlining logic. There was a good reason to remove reparenting/emptying the memcg during the offline. Considering that you can offload force_empty from userspace trivially then I do not see any reason to implement it in the kernel. > > I think it is more important to discuss whether we want to introduce > > force_empty in cgroup v2. > > We would prefer have it in v2 as well. Then bring this up in a separate email thread please. -- Michal Hocko SUSE Labs