Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757387AbaDBCLy (ORCPT ); Tue, 1 Apr 2014 22:11:54 -0400 Received: from mail-pb0-f73.google.com ([209.85.160.73]:43473 "EHLO mail-pb0-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650AbaDBCLw (ORCPT ); Tue, 1 Apr 2014 22:11:52 -0400 References: <1396235199.2507.2.camel@buesod1.americas.hpqcorp.net> <20140331170546.3b3e72f0.akpm@linux-foundation.org> <1396371699.25314.11.camel@buesod1.americas.hpqcorp.net> <1396377083.25314.17.camel@buesod1.americas.hpqcorp.net> <1396386062.25314.24.camel@buesod1.americas.hpqcorp.net> <20140401142947.927642a408d84df27d581e36@linux-foundation.org> <20140401144801.603c288674ab8f417b42a043@linux-foundation.org> <533B6EC0.10303@jp.fujitsu.com> User-agent: mu4e 0.9.9.6pre2; emacs 24.3.1 From: Greg Thelen To: Kamezawa Hiroyuki Cc: Davidlohr Bueso , KOSAKI Motohiro , Andrew Morton , Manfred Spraul , aswin@hp.com, LKML , "linux-mm\@kvack.org" Subject: Re: [PATCH] ipc,shm: increase default size for shmmax In-reply-to: <533B6EC0.10303@jp.fujitsu.com> Date: Tue, 01 Apr 2014 19:11:51 -0700 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 01 2014, Kamezawa Hiroyuki wrote: >> On Tue, Apr 01 2014, Davidlohr Bueso wrote: >> >>> On Tue, 2014-04-01 at 19:56 -0400, KOSAKI Motohiro wrote: >>>>>>> Ah-hah, that's interesting info. >>>>>>> >>>>>>> Let's make the default 64GB? >>>>>> >>>>>> 64GB is infinity at that time, but it no longer near infinity today. I like >>>>>> very large or total memory proportional number. >>>>> >>>>> So I still like 0 for unlimited. Nice, clean and much easier to look at >>>>> than ULONG_MAX. And since we cannot disable shm through SHMMIN, I really >>>>> don't see any disadvantages, as opposed to some other arbitrary value. >>>>> Furthermore it wouldn't break userspace: any existing sysctl would >>>>> continue to work, and if not set, the user never has to worry about this >>>>> tunable again. >>>>> >>>>> Please let me know if you all agree with this... >>>> >>>> Surething. Why not. :) >>> >>> *sigh* actually, the plot thickens a bit with SHMALL (total size of shm >>> segments system wide, in pages). Currently by default: >>> >>> #define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16)) >>> >>> This deals with physical memory, at least admins are recommended to set >>> it to some large percentage of ram / pagesize. So I think that if we >>> loose control over the default value, users can potentially DoS the >>> system, or at least cause excessive swapping if not manually set, but >>> then again the same goes for anon mem... so do we care? >> > (2014/04/02 10:08), Greg Thelen wrote: >> >> At least when there's an egregious anon leak the oom killer has the >> power to free the memory by killing until the memory is unreferenced. >> This isn't true for shm or tmpfs. So shm is more effective than anon at >> crushing a machine. > > Hm..sysctl.kernel.shm_rmid_forced won't work with oom-killer ? > > http://www.openwall.com/lists/kernel-hardening/2011/07/26/7 > > I like to handle this kind of issue under memcg but hmm..tmpfs's limit is half > of memory at default. Ah, yes. I forgot about shm_rmid_forced. Thanks. It would give the oom killer ability to cleanup shm (as it does with anon) when shm_rmid_forced=1. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/