linux-kernel - Re: [PATCH 0/9] OpenVZ kernel based checkpointing/restart

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Message-ID: <20080903140636.GS14473@hawkmoon.kerlabs.com>
Date:	Wed, 3 Sep 2008 16:06:37 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Andrey Mirkin <major@...nvz.org>
Cc:	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] OpenVZ kernel based checkpointing/restart

On Wed, Sep 03, 2008 at 03:49:51PM +0200, Louis Rilling wrote:
> On Wed, Sep 03, 2008 at 02:57:47PM +0400, Andrey Mirkin wrote:
> > This patchset introduces kernel based checkpointing/restart as it is
> > implemented in OpenVZ project. This patchset has limited functionality and
> > are able to checkpoint/restart only single process. Recently Oren Laaden
> > sent another kernel based implementation of checkpoint/restart. The main
> > differences between this patchset and Oren's patchset are:
> > 
> > * In this patchset checkpointing initiated not from the process
> > (right now we do not have a container, only namespaces), Oren's patchset
> > performs checkpointing from the process context.
> > 
> > * Restart in this patchset is initiated from process, which restarts a new
> > process (in new namespaces) with saved state. Oren's patchset uses the same
> > process from which restart was initiated and restore saved state over it.
> > 
> > * Checkpoint/restart functionality in this patchset is implemented as a kernel
> > module
> > 
> > 
> > As checkpointing is initiated not from the process which state should be saved
> > we should freeze a process before saving its state. Right now Container Freezer
> > from Matt Helsley can be used for this.
> > 
> > This patchset introduce only a concept how kernel based checkpointing/restart
> > can be implemented and are able to checkpoint/restart only a single process
> > with simple VMAs. 
> > 
> > I've tried to split my patchset in small patches to make review more easier.
> 
> Thank you Andrey for having highlighted the differences with Oren's approach,
> and for having split this patchset. Few remarks in reply to the patches.

Forgot a global comment: you will probably get the same (rather pointless for a
proof of concept, IMHO) requests as Oren got, to
1) improve coding style:
  a) especially avoid error handling like:
	err = foo();
	if (!err)
		err = bar();
	if (!err)
		err = baz();

and prefer
	err = foo();
	if (err)
		goto foo_err;
	err = bar();
	...

  b) do not write conditions on a single line, like
	if (foo) bar;

2) put arch-dependent code in arch/ subdirs.
3) I probably forgot other ones.

I obviously do not personally request you to take these requests into account ;)

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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