linux-kernel - Re: GRU driver feedback

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Date:	Thu, 31 Jul 2008 07:40:39 -0500
From:	Jack Steiner <steiner@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Robin Holt <holt@....com>,
	"Torvalds, Linus" <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: GRU driver feedback

On Thu, Jul 31, 2008 at 05:14:04PM +1000, Nick Piggin wrote:
> On Wednesday 30 July 2008 15:50, Nick Piggin wrote:
> > On Wednesday 30 July 2008 04:53, Robin Holt wrote:
> 
> > > In the case where unmap_region is clearing page tables, the caller to
> > > unmap_region is expected to be holding the mmap_sem writably.  Jacks
> > > fault handler will immediately return when it fails on the
> > > down_read_trylock().
> >
> > No, you are right of course. I had in my mind the problems faced by
> > lockless get_user_pages, in which case I was worried about the page table
> > existence, but missed the fact that you're holding mmap_sem to provide
> > existence (which it would, as you note, although one day we may want to
> > reclaim page tables or something that doesn't take mmap_sem, so a big
> > comment would be nice here).
> 
> The other thing is... then GRU should get rid of the local_irq_disable
> in the atomic pte lookup. By definition it is worthless if we can be
> operating on an mm that is not running on current (and if I understand
> correctly, sn2 can avoid sending tlb flush IPIs completely sometimes?)

Done.

I'm collecting the fixes & additional comments to be added & will send
them upstream later.

Thanks for the careful review.


--- jack
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