linux-kernel - Re: [PATCH 3/3] pids: Make it possible to clone tasks with given pids

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Date:	Fri, 11 Nov 2011 17:48:00 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Nathan Lynch <ntl@...ox.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Serge Hallyn <serue@...ibm.com>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [PATCH 3/3] pids: Make it possible to clone tasks with given
	pids

On 11/11, Pavel Emelyanov wrote:
>
> First of all - let's imagine that we just want to clone a set of tasks. Then
> each of them will have to fork its kids, then report first of them that he's
> OK to fork and wait for it to report back, that forking is done. Then do the
> same for the rest of them. This is not impossible, but painful.

Why we should wait/report? They can do this in parallel, only
"set_last_pid + fork" needs the synchronization or "check + retry".

> Next - let's consider we have some tasks sharing various resources, e.g. mm-s
> or fd-tables. This means, that these tasks should be cloned in the carefully
> calculated sequence with CLONE_XXX flags set. In this case the described above
> scheme with fork() serialization simply won't work and we'll have to invent
> some fancy messaging with "now X fork with Y pid" and "X done with forking,
> please go on" messages.

Can't understand...

Oleg.

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