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[2003:d9:93c7:4c00:fc5a:ea9:bddf:9934]) by smtp.googlemail.com with ESMTPSA id j124-v6sm1520352wmb.1.2018.11.20.11.45.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Nov 2018 11:45:19 -0800 (PST) Subject: Re: [PATCH v11 1/3] ipc: Allow boot time extension of IPCMNI from 32k to 16M To: Waiman Long , "Luis R. Rodriguez" , Kees Cook , Andrew Morton , Jonathan Corbet Cc: 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 References: <1541794292-19425-1-git-send-email-longman@redhat.com> <1541794292-19425-2-git-send-email-longman@redhat.com> From: Manfred Spraul Message-ID: Date: Tue, 20 Nov 2018 20:45:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <1541794292-19425-2-git-send-email-longman@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/9/18 9:11 PM, 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, especially > those that are migrating from Solaris which uses 24 bits for unique > identifiers. To satisfy the need of those users, a new boot time kernel > option "ipcmni_extend" is added to extend the IPCMNI value to 16M. This > is a 512X increase which should be big enough for users out there that > need a large number of unique IPC identifier. > > The use of this new option will change the pattern of the IPC identifiers > returned by functions like shmget(2). An application that depends on > such pattern may not work properly. So it should only be used if the > users really need more than 32k of unique IPC numbers. > > This new option does have the side effect of reducing the maximum number > of unique sequence numbers from 64k down to 128. So it is a trade-off. > > The computation of a new IPC id is not done in the performance critical > path. So a little bit of additional overhead shouldn't have any real > performance impact. > > Signed-off-by: Waiman Long Acked-by: Manfred Spraul