Messages in this thread | | | Date | Mon, 25 Apr 2005 15:32:56 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation |
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Timur Tabi <timur.tabi@ammasso.com> wrote: > > Andrew Morton wrote: > > > The way we expect get_user_pages() to be used is that the kernel will use > > get_user_pages() once per application I/O request. > > > > Are you saying that RDMA clients will semi-permanently own pages which were > > pinned by get_user_pages()? That those pages will be used for multiple > > separate I/O operations? > > Yes, absolutely! > > The memory buffer is allocated by the process (usually just via malloc) and > registed/pinned by the driver. It then stays pinned for the life of the process (typically).
ug. What stops the memory from leaking if the process exits?
I hope this is a privileged operation?
> > If so, then that's a significant design departure and it would be good to > > hear why it is necessary. > > That's just how RMDA works. Once the memory is pinned, if the app wants to send data to > another node, it does two things: > > 1) Puts the data into its buffer > 2) Sends a "work request" to the driver with (among other things) the offset and length of > the data. > > This is a time-critical operation. It must occurs as fast as possible, which means the > memory must have already been pinned.
It would be better to obtain this memory via a mmap() of some special device node, so we can perform appropriate permission checking and clean everything up on unclean application exit.
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