From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAE61C4321D for ; Sat, 18 Aug 2018 01:15:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7846C21890 for ; Sat, 18 Aug 2018 01:15:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7846C21890 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726126AbeHREV2 (ORCPT ); Sat, 18 Aug 2018 00:21:28 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:33642 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725868AbeHREV2 (ORCPT ); Sat, 18 Aug 2018 00:21:28 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 83A18B796; Sat, 18 Aug 2018 01:15:45 +0000 (UTC) Received: from llong.remote.csb (ovpn-120-191.rdu2.redhat.com [10.10.120.191]) by smtp.corp.redhat.com (Postfix) with ESMTP id F2B3510075E8; Sat, 18 Aug 2018 01:15:43 +0000 (UTC) Subject: Re: [PATCH v8 3/5] ipc: Allow boot time extension of IPCMNI from 32k to 2M To: Davidlohr Bueso Cc: "Luis R. Rodriguez" , Kees Cook , Andrew Morton , Jonathan Corbet , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, Al Viro , Matthew Wilcox , "Eric W. Biederman" , Takashi Iwai , Davidlohr Bueso , manfred@colorfullife.com References: <1529317698-16575-1-git-send-email-longman@redhat.com> <1529317698-16575-4-git-send-email-longman@redhat.com> <20180817164548.GA32382@linux-r8p5> From: Waiman Long Organization: Red Hat Message-ID: <5ddb67bb-872b-c8c1-7838-2622195ae1fc@redhat.com> Date: Fri, 17 Aug 2018 21:15:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20180817164548.GA32382@linux-r8p5> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Sat, 18 Aug 2018 01:15:45 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Sat, 18 Aug 2018 01:15:45 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'longman@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/17/2018 12:45 PM, Davidlohr Bueso wrote: > Cc'ing Manfred. > > On Mon, 18 Jun 2018, Waiman Long wrote: > >> The maximum number of unique System V IPC identifiers was limited to >> 32k. That limit should be big enough for most use cases. >> >> However, there are some users out there requesting for more. To satisfy >> the need of those users, a new boot time kernel option "ipcmni_extend" >> is added to extend the IPCMNI value to 2M. This is a 64X increase which >> hopefully is big enough for them. > > Could you please provide more info on the need of these users and how > you came up with this new value (which just seems quite arbitrary)? > > Thanks, > Davidlohr Red Hat has a customer that is migrating from Solaris to Linux. Some of their applications just happen to use more than 32k of shared memory segments. I think Solaris allows up to 16M unique ID. Yes, the amount of increase is a bit arbitrary. I was trying to balance how many bits should be left for sequence number. Maybe I should just take 8 more bits for ID and leave 8 bits for sequence number to match Solaris. -Longman