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[2003:d9:93c7:7b00:b5eb:8db1:7949:446]) by smtp.googlemail.com with ESMTPSA id k7-v6sm15661196wmf.41.2018.10.02.09.32.15 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Oct 2018 09:32:15 -0700 (PDT) Subject: Re: [PATCH v8 3/5] ipc: Allow boot time extension of IPCMNI from 32k to 2M To: Waiman Long , 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 References: <1529317698-16575-1-git-send-email-longman@redhat.com> <1529317698-16575-4-git-send-email-longman@redhat.com> <20180817164548.GA32382@linux-r8p5> <5ddb67bb-872b-c8c1-7838-2622195ae1fc@redhat.com> From: Manfred Spraul Message-ID: <02ebafee-a295-58cf-044e-e2df0e878e0d@colorfullife.com> Date: Tue, 2 Oct 2018 18:32:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <5ddb67bb-872b-c8c1-7838-2622195ae1fc@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hello together, On 8/18/18 3:15 AM, Waiman Long wrote: > 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. - I think we should use the same numbers as Solaris. Otherwise we later have to touch it again. - What is the performance when using shmget() with already 10M segments present? - I like the new logic for updating the sequence counter. Is there a reason why you only enable it for extended mode? You create a rarely used codepath, and I don't understand what speaks against switching to the 'deleted' approach for all systems. --     Manfred