Re: Implement lookup_swap_cache for migration entries

[Christoph Lameter]

On Fri, 14 Apr 2006, Andrew Morton wrote:

> So we're doing a get_page() on a random page which could be in any state -
> it could be on the freelists, or in the per-cpu pages arrays, it could have
> been reused for something else.

Hmmm... Yes, Ahh! The tree_lock prohibits this sort of thing from 
happening to regular pages. Right.... Yuck this could be expensive to fix.

We are holding the anon_vma lock while remapping migration ptes. So we 
could take the anonvma lock, check to see if the pte is still a migration
pte if so then it cannot change and we can safely increase page 
count.
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