Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757356AbaDBCBt (ORCPT ); Tue, 1 Apr 2014 22:01:49 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:48565 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755118AbaDBCBs (ORCPT ); Tue, 1 Apr 2014 22:01:48 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <533B6EC0.10303@jp.fujitsu.com> Date: Wed, 02 Apr 2014 10:58:24 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Greg Thelen , Davidlohr Bueso CC: KOSAKI Motohiro , Andrew Morton , Manfred Spraul , aswin@hp.com, LKML , "linux-mm@kvack.org" Subject: Re: [PATCH] ipc,shm: increase default size for shmmax 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> <1396394931.25314.34.camel@buesod1.americas.hpqcorp.net> <1396399239.25314.47.camel@buesod1.americas.hpqcorp.net> In-Reply-To: Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/04/02 10:08), Greg Thelen 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? > > 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. Thanks, -Kame -- 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/