Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753350AbaDROzH (ORCPT ); Fri, 18 Apr 2014 10:55:07 -0400 Received: from fujitsu25.fnanic.fujitsu.com ([192.240.6.15]:60230 "EHLO fujitsu25.fnanic.fujitsu.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752263AbaDROzC convert rfc822-to-8bit (ORCPT ); Fri, 18 Apr 2014 10:55:02 -0400 From: Motohiro Kosaki To: Manfred Spraul , Andrew Morton , Davidlohr Bueso CC: LKML , KAMEZAWA Hiroyuki , Motohiro Kosaki JP , "gthelen@google.com" , "aswin@hp.com" , "linux-mm@kvack.org" , "mtk.manpages@gmail.com" Date: Fri, 18 Apr 2014 07:54:36 -0700 Subject: RE: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity Thread-Topic: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity Thread-Index: Ac9a5z2umjBksE+wSTKA+wv1IS9RrAALr2nA Message-ID: <6B2BA408B38BA1478B473C31C3D2074E30986F0FF0@SV-EXCHANGE1.Corp.FC.LOCAL> References: <1397812720-5629-1-git-send-email-manfred@colorfullife.com> In-Reply-To: <1397812720-5629-1-git-send-email-manfred@colorfullife.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.11.96,1.0.14,0.0.0000 definitions=2014-04-18_01:2014-04-18,2014-04-18,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Manfred Spraul [mailto:manfred@colorfullife.com] > Sent: Friday, April 18, 2014 2:19 AM > To: Andrew Morton; Davidlohr Bueso > Cc: LKML; KAMEZAWA Hiroyuki; Motohiro Kosaki JP; gthelen@google.com; aswin@hp.com; linux-mm@kvack.org; Manfred Spraul; > mtk.manpages@gmail.com > Subject: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity > > System V shared memory > > a) can be abused to trigger out-of-memory conditions and the standard > measures against out-of-memory do not work: > > - it is not possible to use setrlimit to limit the size of shm segments. > > - segments can exist without association with any processes, thus > the oom-killer is unable to free that memory. > > b) is typically used for shared information - today often multiple GB. > (e.g. database shared buffers) > > The current default is a maximum segment size of 32 MB and a maximum total size of 8 GB. This is often too much for a) and not > enough for b), which means that lots of users must change the defaults. > > This patch increases the default limits to ULONG_MAX, which is perfect for case b). The defaults are used after boot and as the initial > value for each new namespace. > > Admins/distros that need a protection against a) should reduce the limits and/or enable shm_rmid_forced. > > Further notes: > - The patch only changes the boot time default, overrides behave as before: > # sysctl kernel/shmall=33554432 > would recreate the previous limit for SHMMAX (for the current namespace). > > - Disabling sysv shm allocation is possible with: > # sysctl kernel.shmall=0 > (not a new feature, also per-namespace) > > - ULONG_MAX is not really infinity, but 18 Exabyte segment size and > 75 Zettabyte total size. This should be enough for the next few weeks. > (assuming a 64-bit system with 4k pages) > > Risks: > - The patch breaks installations that use "take current value and increase > it a bit". [seems to exist, http://marc.info/?l=linux-mm&m=139638334330127] > After a: > # CUR=`sysctl -n kernel.shmmax` > # NEW=`echo $CUR+1 | bc -l` > # sysctl -n kernel.shmmax=$NEW > shmmax ends up as 0, which disables shm allocations. > > - There is no wrap-around protection for ns->shm_ctlall, i.e. the 75 ZB > limit is not enforced. > > Signed-off-by: Manfred Spraul > Reported-by: Davidlohr Bueso > Cc: mtk.manpages@gmail.com I'm ok either ULONG_MAX or 0 (special value of infinity). Acked-by: KOSAKI Motohiro -- 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/