linux-kernel - Re: [PATCH 0/4] ipc/shm.c: increase the limits for SHMMAX, SHMALL

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Date:	Tue, 03 Jun 2014 12:26:00 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	mtk.manpages@...il.com
Cc:	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.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 0/4] ipc/shm.c: increase the limits for SHMMAX, SHMALL

On Fri, 2014-05-02 at 15:16 +0200, Michael Kerrisk (man-pages) wrote:
> Hi Manfred,
> 
> On Mon, Apr 21, 2014 at 4:26 PM, Manfred Spraul
> <manfred@...orfullife.com> wrote:
> > Hi all,
> >
> > the increase of SHMMAX/SHMALL is now a 4 patch series.
> > I don't have ideas how to improve it further.
> 
> On the assumption that your patches are heading to mainline, could you
> send me a man-pages patch for the changes?

It seems we're still behind here and the 3.16 merge window is already
opened. Please consider this, and again feel free to add/modify as
necessary. I think adding a note as below is enough and was hesitant to
add a lot of details... Thanks.

8<--------------------------------------------------
From: Davidlohr Bueso <davidlohr@...com>
Subject: [PATCH] shmget.2: document new limits for shmmax/shmall

These limits have been recently enlarged and
modifying them is no longer really necessary.
Update the manpage.

Signed-off-by: Davidlohr Bueso <davidlohr@...com>
---
 man2/shmget.2 | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/man2/shmget.2 b/man2/shmget.2
index f781048..77764ea 100644
--- a/man2/shmget.2
+++ b/man2/shmget.2
@@ -299,6 +299,11 @@ with 8kB page size, it yields 2^20 (1048576).
 
 On Linux, this limit can be read and modified via
 .IR /proc/sys/kernel/shmall .
+As of Linux 3.16, the default value for this limit is increased to
+.B ULONG_MAX - 2^24
+pages, which is as large as it can be without helping userspace overflow
+the values. Modifying this limit is therefore discouraged. This is suitable
+for both 32 and 64-bit systems.
 .TP
 .B SHMMAX
 Maximum size in bytes for a shared memory segment.
@@ -306,6 +311,12 @@ Since Linux 2.2, the default value of this limit is 0x2000000 (32MB).
 
 On Linux, this limit can be read and modified via
 .IR /proc/sys/kernel/shmmax .
+As of Linux 3.16, the default value for this limit is increased from 32Mb
+to
+.B ULONG_MAX - 2^24
+bytes, which is as large as it can be without helping userspace overflow
+the values. Modifying this limit is therefore discouraged. This is suitable
+for both 32 and 64-bit systems.
 .TP
 .B SHMMIN
 Minimum size in bytes for a shared memory segment: implementation
-- 
1.8.1.4



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