[openib-general] Question about pinning memory

[Pete Wyckoff]

glebn at voltaire.com wrote on Wed, 27 Jul 2005 10:02 +0300:
> Then we understand Pete differently. This is what he wrote in his first
> email on the subject:
>    The MPI library essentially makes a system call before
>    reusing a cached memory registration to verify it is still valid.
> How "the MPI library just checks the queue of VM events" without system
> call? Do you mean kernel dumps events in some preallocated memory in
> user process address space?

Roland has it right.  In response to your comments I refined the
mechanism to avoid the system call:  the kernel writes an event
count to a registered userspace integer when something changes.

> Of cause it is possible. It seems you misunderstand me. What is not
> possible is that this happens between malloc() and free() for pinned
> memory. After user does free() on a chunk of pinned memory we do not
> unpin memory till libc returns this memory to the kernel via
> munmap()/sbrk() system calls. Again this is what I already wrote.
> 
> The solution that I what to see is this:
> 1) Program knows somehow (without system call) that vma list changes.
> 2) Program fetch new vma list (possibly by using system call).
> 3) Program unregister cached entries that are no longer in virtual address
> space.

This is what I did.  I'll just clean up the code and post it so you
can read it yourself.

		-- Pete