From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f199.google.com (mail-lb0-f199.google.com [209.85.217.199]) by kanga.kvack.org (Postfix) with ESMTP id A53006B007E for ; Fri, 13 May 2016 04:44:45 -0400 (EDT) Received: by mail-lb0-f199.google.com with SMTP id tb5so25032978lbb.3 for ; Fri, 13 May 2016 01:44:45 -0700 (PDT) Received: from smtp2-g21.free.fr (smtp2-g21.free.fr. [212.27.42.2]) by mx.google.com with ESMTPS id g198si2577913wmd.58.2016.05.13.01.44.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 May 2016 01:44:44 -0700 (PDT) Subject: Re: [PATCH] mm: add config option to select the initial overcommit mode References: <5731CC6E.3080807@laposte.net> <20160513080458.GF20141@dhcp22.suse.cz> From: Mason Message-ID: <573593EE.6010502@free.fr> Date: Fri, 13 May 2016 10:44:30 +0200 MIME-Version: 1.0 In-Reply-To: <20160513080458.GF20141@dhcp22.suse.cz> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Sebastian Frias Cc: linux-mm@kvack.org, Andrew Morton , Linus Torvalds , LKML On 13/05/2016 10:04, Michal Hocko wrote: > On Tue 10-05-16 13:56:30, Sebastian Frias wrote: > [...] >> NOTE: I understand that the overcommit mode can be changed dynamically thru >> sysctl, but on embedded systems, where we know in advance that overcommit >> will be disabled, there's no reason to postpone such setting. > > To be honest I am not particularly happy about yet another config > option. At least not without a strong reason (the one above doesn't > sound that way). The config space is really large already. > So why a later initialization matters at all? Early userspace shouldn't > consume too much address space to blow up later, no? One thing I'm not quite clear on is: why was the default set to over-commit on? I suppose the biggest use-case is when a "large" process forks only to exec microseconds later into a "small" process, it would be silly to refuse that fork. But isn't that what the COW optimization addresses, without the need for over-commit? Another issue with overcommit=on is that some programmers seem to take for granted that "allocations will never fail" and so neglect to handle malloc == NULL conditions gracefully. I tried to run LTP with overcommit off, and I vaguely recall that I had more failures than with overcommit on. (Perhaps only those tests that tickle the dreaded OOM assassin.) Regards. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org