linux-kernel - Re: C/R without "leaks"

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Message-ID: <m3ocupmtkq.fsf@pobox.com>
Date:	Tue, 21 Apr 2009 19:16:05 -0500
From:	Nathan Lynch <ntl@...ox.com>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	containers@...ts.osdl.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: C/R without "leaks"

Oren Laadan <orenl@...columbia.edu> writes:
> Alexey Dobriyan wrote:
>>> Again, so to checkpoint one task in the topmost pid-ns you need to
>>> checkpoint (if at all possible) the entire system ?!
>> 
>> One more argument to not allow "leaks" and checkpoint whole container,
>> no ifs, buts and woulditbenices.
>> 
>> Just to clarify, C/R with "leak" is for example when process has separate
>> pidns, but shares, for example, netns with other process not involved in
>> checkpoint.
>> 
>> If you allow this, you lose one important property of checkpoint part,
>> namely, almost everything is frozen. Losing this property means suddenly
>> much more stuff is alive during dump and you has to account to more stuff
>> when checkpointing. You effectively checkpointing on live data structures
>> and there is no guarantee you'll get it right.
>
> Alexey, we're entirely on par about this: everyone agrees that if you
> want the maximal guarantee (if one exists) you must checkpoint entire
> container and have no leaks.
>
> The point I'm stressing is that there are other use cases, and other
> users, that can do great things even without full container. And my
> goal is to provide them this capability.

As it seems that Alexey's goal is more or less a subset of yours, would
it make sense in the near term to concentrate on getting an
implementation upstream that satisfies that subset (i.e. checkpoint on a
container basis only)?  And then support for checkpointing arbitrary
processes could be added later, if it proves feasible?
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