linux-kernel - Re: [PATCH v2] Add /proc/pid

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Message-ID: <20181122135834.GA29449@uranus>
Date:   Thu, 22 Nov 2018 16:58:34 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Daniel Colascione <dancol@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Tim Murray <timmurray@...gle.com>,
        Primiano Tucci <primiano@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com>,
        Prashant Dhamdhere <pdhamdhe@...hat.com>,
        "Dennis Zhou (Facebook)" <dennisszhou@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, rostedt@...dmis.org,
        tglx@...utronix.de, mingo@...nel.org, linux@...inikbrodowski.net,
        jpoimboe@...hat.com, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        ktsanaktsidis@...desk.com, David Howells <dhowells@...hat.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2] Add /proc/pid_gen

On Wed, Nov 21, 2018 at 04:35:34PM -0700, Andy Lutomirski wrote:
> > 
> > I'm going to have Android's systrace and Perfetto use this approach.
> > Exactly how many tools signed up to use this feature do you need?
> > 
> >> Those people are the intended audience and the
> >> best-positioned reviewers so let's hear from them?
> > 
> > I'm writing plenty of trace analysis tools myself, so I'm part of this
> > intended audience. Other tracing tool authors have told me about
> > out-of-tree hacks for process atomic snapshots via ftrace events. This
> > approach avoids the necessity of these more-invasive hacks.
> 
> Would a tracepoint for pid reuse solve your problem?

FWIW we've had similar problem in criu for memory snapshotting,
because memory data is PID-driven and snapshots are rather
discrete events. So we use task_struct::real_start_time as
a second guard agains pid reuse.