Re: Ummunotify: progress at last!

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > > I wonder, is that a win?  I guess you don't even have to pin it, just do
 > > copy_to_user() to update the counter, but mmap doesn't seem so bad.
 > 
 > Not sure you can call copy_to_user from a mmu_notifier callback? What
 > if it faults?

Good point... we could defer it to a context where we could block but...

 > I think the idea would be that by letting user space select the
 > counter location it could place it in a sensible cachline/etc and
 > probably avoid a pointer indirection.

OK, I have to look at the perf stuff.  That makes sense but OTOH
userspace could (unknowingly) pick a highmen page and then we end up
having to do kmap_atomic or something from an mmu notifier callback.
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Roland Dreier  <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>
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