From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757465Ab3HGN5j (ORCPT ); Wed, 7 Aug 2013 09:57:39 -0400 Received: from cantor2.suse.de ([195.135.220.15]:60697 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752893Ab3HGN5h (ORCPT ); Wed, 7 Aug 2013 09:57:37 -0400 Date: Wed, 7 Aug 2013 15:57:34 +0200 From: Michal Hocko To: Tejun Heo Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Johannes Weiner , KAMEZAWA Hiroyuki , Andrew Morton , "Kirill A. Shutemov" , Anton Vorontsov Subject: Re: [PATCH 2/3] memcg: Limit the number of events registered on oom_control Message-ID: <20130807135734.GK8184@dhcp22.suse.cz> References: <1375874907-22013-1-git-send-email-mhocko@suse.cz> <1375874907-22013-2-git-send-email-mhocko@suse.cz> <20130807130836.GB27006@htj.dyndns.org> <20130807133746.GI8184@dhcp22.suse.cz> <20130807134741.GF27006@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130807134741.GF27006@htj.dyndns.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 07-08-13 09:47:41, Tejun Heo wrote: > Hello, > > On Wed, Aug 07, 2013 at 03:37:46PM +0200, Michal Hocko wrote: > > > It isn't different from listening from epoll, for example. > > > > epoll limits the number of watchers, no? > > Not that I know of. It'll be limited by max open fds but I don't > think there are other limits. max_user_watches seems to be a limit (4% of lowmem in maximum). > Why would there be? Because userspace should hog kernel resources without any limit. > > > If there needs to be kernel memory limit, shouldn't that be handled by > > > kmemcg? > > > > kmemcg would surely help but turning it on just because of potential > > abuse of the event registration API sounds like an overkill. > > > > I think having a cap for user trigable kernel resources is a good thing > > in general. > > I don't know. It's just very arbitrary because listening to events > itself isn't (and shouldn't) be something which consumes resource > which isn't attributed to the listener and this artificially creates a > global resource. The problem with memory usage event is breaching > that rule with shared kmalloc() so putting well-defined limit on it is > fine but the latter two create additional artificial restrictions > which are both unnecessary and unconventional. No? Hmm, OK so you think that the fd limit is sufficient already? -- Michal Hocko SUSE Labs