linux-kernel - Re: [PATCH] ipc,shm: disable shmmax and shmall by default

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Date:	Thu, 03 Apr 2014 21:02:21 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Davidlohr Bueso <davidlohr@...com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, aswin@...com,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Greg Thelen <gthelen@...gle.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] ipc,shm: disable shmmax and shmall by default

Hi Davidlohr,

On 04/03/2014 02:20 AM, Davidlohr Bueso wrote:
> The default size for shmmax is, and always has been, 32Mb.
> Today, in the XXI century, it seems that this value is rather small,
> making users have to increase it via sysctl, which can cause
> unnecessary work and userspace application workarounds[1].
>
> Instead of choosing yet another arbitrary value, larger than 32Mb,
> this patch disables the use of both shmmax and shmall by default,
> allowing users to create segments of unlimited sizes. Users and
> applications that already explicitly set these values through sysctl
> are left untouched, and thus does not change any of the behavior.
>
> So a value of 0 bytes or pages, for shmmax and shmall, respectively,
> implies unlimited memory, as opposed to disabling sysv shared memory.
> This is safe as 0 cannot possibly be used previously as SHMMIN is
> hardcoded to 1 and cannot be modified.
Are we sure that no user space apps uses shmctl(IPC_INFO) and prints a 
pretty error message if shmall is too small?
We would break these apps.

--
     Manfred
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