[ofiwg] fork support and MR cache
jgg at ziepe.ca
Thu Oct 8 11:00:56 PDT 2020
On Thu, Oct 08, 2020 at 05:45:31PM +0000, Hefty, Sean wrote:
> > > There have been extensive discussions on github around the MR cache,
> > > deadlocks, libibverbs madvise tracking, and fork. The current
> > > direction is to only enable the MR cache when fork is disabled.
> > > This was done to work-around internal libibverbs tracking. But I
> > > suspect that bypassing that tracking (which is possible) can still
> > > lead to issues when registrations are made through the MR cache.
> > MADV_DONTFORK will be obsolete starting in kernel v5.9
> > If you can test and confirm that everything works without it then we
> > can detect and disable ibv_fork_init on new kernels.
> Interesting. What will the behavior be for registered regions when fork is called?
They are copied into the fork.
> My concern is that the registrations are made and maintained without
> the application being aware. Will cached registrations need to be
> released when fork is invoked, or is there some other mechanism
> coming into play now?
MRs continue to reliably point to memory owned in the parent
The child process will be unable to use any MRs or verbs objects, just
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