From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Manfred Spraul <manfred@colorfullife.com>,
Davidlohr Bueso <davidlohr@hp.com>
Cc: mtk.manpages@gmail.com, Andrew Morton <akpm@linux-foundation.org>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
LKML <linux-kernel@vger.kernel.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
gthelen@google.com, aswin@hp.com, linux-mm@kvack.org
Subject: Re: [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity
Date: Sat, 19 Apr 2014 11:17:53 +0200 [thread overview]
Message-ID: <53523F41.2080601@gmail.com> (raw)
In-Reply-To: <535235DE.5080304@colorfullife.com>
On 04/19/2014 10:37 AM, Manfred Spraul wrote:
> On 04/19/2014 08:55 AM, Davidlohr Bueso wrote:
>> On Fri, 2014-04-18 at 11:18 +0200, Manfred Spraul wrote:
>>> - 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)
> Note: I found three integer overflows, none of them critical.
> I will send patches, I just must get a 32-bit test setup first.
>>> 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.
> That's why I mentioned it.
> For shmmax, there is a simple answer: Use TASK_SIZE instead of ULONG_MAX.
> - sufficiently far away from overflow.
> - values beyond TASK_SIZE are useless anyway, you can't map such segments.
>
> I don't have a good answer for shmall. 1L<<(BITS_PER_LONG-1) is too ugly.
> Any proposals?
If shmmax is TASK_SIZE, would not the existing
#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16))
suffice?
--
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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prev parent reply other threads:[~2014-04-19 9:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-18 9:18 [PATCH] ipc/shm: Increase the defaults for SHMALL, SHMMAX to infinity Manfred Spraul
2014-04-18 14:54 ` Motohiro Kosaki
2014-04-19 6:55 ` Davidlohr Bueso
2014-04-19 7:10 ` Michael Kerrisk (man-pages)
2014-04-19 8:45 ` Manfred Spraul
2014-04-19 9:14 ` Michael Kerrisk (man-pages)
2014-04-19 8:37 ` Manfred Spraul
2014-04-19 9:17 ` Michael Kerrisk (man-pages) [this message]
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