linux-kernel - Re: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity

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Message-ID: <53523E93.4060702@gmail.com>
Date:	Sat, 19 Apr 2014 11:14:59 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr@...com>
CC:	mtk.manpages@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Greg Thelen <gthelen@...gle.com>, aswin@...com,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to
 infinity

On 04/19/2014 10:45 AM, Manfred Spraul wrote:
> On 04/19/2014 09:10 AM, Michael Kerrisk (man-pages) wrote:
>> On Sat, Apr 19, 2014 at 8:55 AM, Davidlohr Bueso <davidlohr@...com> wrote:
>>> On Fri, 2014-04-18 at 11:18 +0200, Manfred Spraul wrote:
>>>> 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]
>>> This really scares me. The probability of occurrence is now much higher,
>>> and not just theoretical. It would legitimately break userspace.
>> I'm missing something. Manfred's patch doesn't actually change the
>> behavior on this point does it? If the problem is more than
>> theoretical, then it _already_ affects users, right? (And they would
>> therefore already be working around the problem.)
> The current default is 32 MB. if some increases it by 1 MB, then the 
> result is 33 MB.
> The new default would be ULONG_MAX. If someone increases it by 1 MB, 
> then the result is 1 MB - 1 byte.

Ahh. Got it now--sorry for being slow.


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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