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"Oren" == Oren Laadan [off-list ref] writes:

Oren> Daniel Lezcano wrote:

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The one exception (and it is a tedious one !) are states in which
the task is already frozen by definition: any ptrace blocking
point where the tracee waits for the tracer to grant permission to
proceed with its execution. Another example is in vfork(), waiting
for completion.

I would say these are perfect places for "may be
non-checkpointable" :)

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).
Waiting for a vforked process to exec is less than a millisecond.
--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia

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