linux-kernel - Re: [PATCH] Add /proc/pid

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Message-ID: <20181121203150.GK3065@bombadil.infradead.org>
Date:   Wed, 21 Nov 2018 12:31:50 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        timmurray@...gle.com, primiano@...gle.com, joelaf@...gle.com,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        "Dennis Zhou (Facebook)" <dennisszhou@...il.com>,
        Prashant Dhamdhere <pdhamdhe@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        David Howells <dhowells@...hat.com>,
        KJ Tsanaktsidis <ktsanaktsidis@...desk.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] Add /proc/pid_generation

On Wed, Nov 21, 2018 at 12:14:44PM -0800, Daniel Colascione wrote:
> This change adds a per-pid-namespace 64-bit generation number,
> incremented on PID rollover, and exposes it via a new proc file
> /proc/pid_generation. By examining this file before and after /proc
> enumeration, user code can detect the potential reuse of a PID and
> restart the task enumeration process, repeating until it gets a
> coherent snapshot.
> 
> PID rollover ought to be rare, so in practice, scan repetitions will
> be rare.

Then why does it need to be 64-bit?