Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751525AbaDAU0g (ORCPT ); Tue, 1 Apr 2014 16:26:36 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:13058 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751236AbaDAU0f (ORCPT ); Tue, 1 Apr 2014 16:26:35 -0400 Message-ID: <1396383989.25314.19.camel@buesod1.americas.hpqcorp.net> Subject: Re: [PATCH] ipc,shm: increase default size for shmmax From: Davidlohr Bueso To: KOSAKI Motohiro Cc: Andrew Morton , Kamezawa Hiroyuki , Manfred Spraul , aswin@hp.com, LKML , "linux-mm@kvack.org" , "Gotou, Yasunori" , chenhanxiao , Gao feng Date: Tue, 01 Apr 2014 13:26:29 -0700 In-Reply-To: References: <1396235199.2507.2.camel@buesod1.americas.hpqcorp.net> <20140331143217.c6ff958e1fd9944d78507418@linux-foundation.org> <1396306773.18499.22.camel@buesod1.americas.hpqcorp.net> <20140331161308.6510381345cb9a1b419d5ec0@linux-foundation.org> <1396308332.18499.25.camel@buesod1.americas.hpqcorp.net> <20140331170546.3b3e72f0.akpm@linux-foundation.org> <533A5CB1.1@jp.fujitsu.com> <20140401121920.50d1dd96c2145acc81561b82@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.4 (3.6.4-3.fc18) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-04-01 at 16:15 -0400, KOSAKI Motohiro wrote: > >> Our middleware engineers has been complaining about this sysctl limit. > >> System administrator need to calculate required sysctl value by making sum > >> of all planned middlewares, and middleware provider needs to write "please > >> calculate systcl param by....." in their installation manuals. > > > > Why aren't people just setting the sysctl to a petabyte? What problems > > would that lead to? > > I don't have much Fujitsu middleware knowledges. But I'd like to explain > very funny bug I saw. > > 1. middleware-A suggest to set SHMMAX to very large value (maybe > LONG_MAX, but my memory was flushed) > 2. middleware-B suggest to set SHMMAX to increase some dozen mega byte. > > Finally, it was overflow and didn't work at all. > > Let's demonstrate. > > # echo 18446744073709551615 > /proc/sys/kernel/shmmax > # cat /proc/sys/kernel/shmmax > 18446744073709551615 > # echo 18446744073709551616 > /proc/sys/kernel/shmmax > # cat /proc/sys/kernel/shmmax > 0 hehe, what a nasty little tunable this is. Reminds me of this: https://access.redhat.com/site/solutions/16333 -- 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/