[openib-general] Question about pinning memory

[Tziporet Koren]

Answers regarding VAPI:

> > Related to the scenario above, here's my questions:
> > 
> > 1. What happens if pinned memory is returned to the OS via sbrk()?  Do 
> > Bad Things happen, or does the kernel portion of Open IB handle this 
> > gracefully?
> > 
> Kernel portion of OpenIB pins physical pages. If you unmap virtual 
> address range from process address space using sbrk or munmap they will 
> stay pinned until deregistered.
> 
> > (if anyone knows what mVAPI does here, that would also be really useful 
> > to know)

VAPI behaves the same as openib in this case.

> > 
> > 2. What happens if the MPI unpins memory that is already out of the 
> > process?  Do Bad Things happen, or does Open IB handle this gracefully?
> > 
> OpenIB should handle this case. It looks up pinned physical pages using
> memory handle returned on register and unpins them. It doesn't scan user
> virtual space during dereg.
> 
> > (if anyone knows what mVAPI does here, that would also be really useful 
> > to know)
> > 

VAPI free the pinned memory and issue a message in /var/log/messages, and
everything is working well.

Tziporet
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