[ofa-general] Re: [PATCH] mmu notifier #v11

[Andrea Arcangeli <andrea@qumranet.com>]

On Sun, Apr 06, 2008 at 10:45:41PM -0700, Christoph Lameter wrote:
> That depends on what the notifier is being used for. Some serialization 
> with the external mappings has to be done anyways. And its cleaner to have 

As far as I can tell no, you don't need to serialize against the
secondary mmu page fault in invalidate_page, like you instead have to
do in range_begin if you don't unpin the pages in range_end.

> one API that does a lock/unlock scheme. Atomic operations can easily lead
> to races.

What races? Note that if you don't want to optimize XPMEM and GRU can
feel free to implement their own invalidate_page as this:

     invalidate_page(mm, addr) {
     	range_begin(mm, addr, addr+PAGE_SIZE)
	range_end(mm, addr, addr+PAGE_SIZE)
     }

There's zero risk of adding races if they do this, but I doubt they
want to run as slow as with EMM so I guess they'll exploit the
optimization by going lock-free vs the spte page fault in
invalidate_page.