[PATCH 0/6] /proc/pid/checkpointable

Cedric Le Goater legoater at free.fr
Thu Mar 26 02:52:10 PDT 2009


Serge E. Hallyn wrote:
> Quoting Eric W. Biederman (ebiederm at xmission.com):
>> Dave Hansen <dave at linux.vnet.ibm.com> writes:
>>
>>> On Wed, 2009-03-18 at 13:03 -0700, Mike Waychison wrote:
>>>> Polluting the dmesg buffer with messages from common failures (consider 
>>>> a multi-user cluster where checkpoints may or may not succeed) isn't 
>>>> very useful.
>>> Yeah, I've already gotten an earful from Serge and Dan S. about this. :)
>>>
>>> Serge suggested that, perhaps, the audit framework could be used.  We
>>> might also use an ftrace buffer if we want to keep a whole ton of
>>> messages around, too.
>>>
>>> dmesg is definitely not workable long-term at all.
>> How about having place holder objects in the generated checkpoint.
>> Then instead of having a failure you have a non-restoreable checkpoint.
>> But you know which fd, or which mmaped region, or which other thing
>> is causing the problem and if you want more information you can
>> look at that resource.
>>
>> That gives user space the freedom and scrub out the non-checkpointable
>> bits and replace them with something like /dev/null so that we can
>> continue on and restore the checkpoint anyway, if we think our
>> app can cope with some things going away.
>>
>> Eric
> 
> I like this idea.

yes. This is something required to replace stdios for example, when 
you execute an application under ssh, checkpoint and then restart on 
an other host. This a topical scenario for a batch manager in an HPC 
environment. 

identified resources of the container are tracked to be ignored by 
checkpoint and to be replaced by similar ones at restart.


C.

> Subystems which are temporarily entirely unsupported (like sysvipc)
> would need at least a dummy section in the format wherein we can at
> least say 'unsupported', otherwise we'll still just get a meaningless
> -EINVAL.
>
> I actually got bitten yesterday by trying to checkpoint a task that
> wasn't frozen.  I forgot v14 had that check, and my failures (a
> segfault actually) weren't helpful.
> 
> -serge
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