[RFC][PATCH 8/8] check files for checkpointability
Serge E. Hallyn
serue at us.ibm.com
Sun Mar 1 09:00:10 PST 2009
Quoting Sukadev Bhattiprolu (sukadev at linux.vnet.ibm.com):
> Dave Hansen [dave at linux.vnet.ibm.com] wrote:
> | Introduce a files_struct counter to indicate whether a particular
> | file_struct has ever contained a file which can not be
> | checkpointed. This flag is a one-way trip; once it is set, it may
> | not be unset.
> | We assume at allocation that a new files_struct is clean and may
> | be checkpointed. However, as soon as it has had its files filled
> | from its parent's, we check it for real in __scan_files_for_cr().
> | At that point, we mark it if it contained any uncheckpointable
> | files.
> Hmm. Why not just copy ->may_checkpoint setting from parent (or old)
> files_struct ? If parent is not checkpointable, then child won't be
> and vice-versa - no ?
No. We don't clear the files_struct checkpointable flag when an
uncheckpointable file is closed. But if the parent has closed
all uncheckpointable files before forking, then the child can
be started with a checkpointable files_struct.
Otherwise it wouldn't just be the task which has a one-way trip to
uncheckpointability, but process trees, and - assuming init does
anything uncheckpointable at all - the whole system :)
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