linux-kernel - Re: [RFC v6][PATCH 0/9] Kernel based checkpoint/restart

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Message-ID: <48F83458.2080602@fr.ibm.com>
Date:	Fri, 17 Oct 2008 08:44:40 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	Peter Chubb <peterc@...ato.unsw.edu.au>
CC:	Oren Laadan <orenl@...columbia.edu>,
	Daniel Lezcano <dlezcano@...ibm.com>, jeremy@...p.org,
	arnd@...db.de, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrey Mirkin <major@...nvz.org>
Subject: Re: [RFC v6][PATCH 0/9] Kernel based checkpoint/restart

> Oren> For now, yes. But we definitely want this capability in the long
> Oren> run; otherwise we won't be able to checkpoint a kernel compile
> Oren> ('make' uses vfork), or anything with 'gdb' running inside, or
> Oren> 'strace', and other goodies.
> 
> The strace/gdb example is *really* hard; but for vfork, you just wait
> until it's over. The interval between vfork and exec/exit should be
> short enough not to affect the overall time for a checkpoint (and
> checkpoint can be fairly slow anyway --- on the HPC machines we used
> to do it on, writing half a terabyte of checkpoint image to disc could take
> many minutes.  In hindsight, we should have multithreaded it).

we've tried that and it doesn't change a thing if you have only one disk :)
it might even give worse results as you are increasing context switches.

> Waiting for a vforked process to exec is less than a millisecond.

yes that shouldn't be too hard to handle.

Cheers,

C.
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