From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753949Ab0ETHHq (ORCPT ); Thu, 20 May 2010 03:07:46 -0400 Received: from cantor2.suse.de ([195.135.220.15]:53366 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752734Ab0ETHHp (ORCPT ); Thu, 20 May 2010 03:07:45 -0400 Date: Thu, 20 May 2010 17:07:41 +1000 From: Nick Piggin To: Manfred Spraul , linux-kernel@vger.kernel.org Subject: [patch 3/3] ipc: increase IPCMNI_MAX Message-ID: <20100520070741.GI2516@laptop> References: <20100520065911.GG2516@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100520065911.GG2516@laptop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Just wondering whether there is a good reason to have a full 16 bits of sequence in ipc ids? 32K indexes is pretty easy to overflow, if only in stress tests for now. I was doing some big aim7 stress testing, which required this patch, but it's not exactly a realistic workload :) But the sequence seems like it just helps slightly with buggy apps, and if the app is buggy then it can by definition mess up its own ids anyway? So I don't see that such amount of seq is required. Index: linux-2.6/ipc/util.h =================================================================== --- linux-2.6.orig/ipc/util.h +++ linux-2.6/ipc/util.h @@ -14,7 +14,16 @@ #include /* IPCMNI_MAX should be <= MAX_INT, absolute limit for ipc arrays */ -#define IPCMNI_MAX_SHIFT 15 +/* + * IPC ids consist of an index into the idr, which allocates from the bottom + * up, and a sequence number which is continually incremented. Valid indexes + * are from 0..IPCMNI_MAX (or further constrained by sysctls or other limits). + * The sequence number prevents ids from being reused quickly. The sequence + * number resides in the top part of the 'int' after IPCMNI_MAX. + * + * Increasing IPCMNI_MAX reduces the sequence wrap interval. + */ +#define IPCMNI_MAX_SHIFT 20 #define IPCMNI_MAX (1 << IPCMNI_MAX_SHIFT) #define SEQ_SHIFT IPCMNI_MAX_SHIFT