Re: [PATCH -mm] remove VM_LOCK_RMAP code

[Nick Piggin <npiggin@suse.de>]

On Mon, Feb 01, 2010 at 10:55:35AM -0500, Rik van Riel wrote:
> On 02/01/2010 01:15 AM, Nick Piggin wrote:
> >On Fri, Jan 29, 2010 at 07:34:10PM -0500, Rik van Riel wrote:
> >>When a VMA is in an inconsistent state during setup or teardown, the
> >>worst that can happen is that the rmap code will not be able to find
> >>the page.
> >
> >OK, but you missed the interesting thing, which is to explain why
> >that worst case is not a problem.
> >
> >rmap of course is not just used for reclaim but also invalidations
> >from mappings, and those guys definitely need to know that all
> >page table entries have been handled by the time they return.
> 
> This is not a problem, because the mapping is in the process
> of being torn down (PTEs just got invalidated by munmap), or
> set up (no PTEs have been instantiated yet).
> 
> The third case is split_vma, where we can have one VMA in an
> inconsistent state (rmap cannot find the PTEs), while the
> other VMA is still in its original state (rmap finds the PTEs
> through that VMA).
> 
> That is what makes this safe.

OK, that sounds fine then. Your changelog was just a bit strange
because you said it would not be able to find the page, which
didn't really make sense.

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