Re: [PATCH v1 3/9] xprtrdma: Introduce ro_unmap_sync method

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On Tue, Nov 24, 2015 at 09:39:33AM -0500, Chuck Lever wrote:
> >> Do we really want to go down that road?  It seems like we've decided
> >> in general that while the protocol specs say MR must be unmapped before
> >> proceeding with the data that is painful enough to ignore this
> >> requirement.  E.g. iser for example only does the local invalidate
> >> just before reusing the MR.
> 
> That leaves the MR exposed to the remote indefinitely. If
> the MR is registered for remote write, that seems hazardous.

Agree.

If we have a performance knob it should be to post the invalidate,
then immediately dma unmap and start using the buffer, not to defer
the invalidate potentially indefinitely.  Then it is just a race to be
exploited not a long lived window into random page cache memory.

Jason
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