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SubjectRe: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages
On Thu, 22 Apr 2010 14:40:46 -0500 (CDT)
Christoph Lameter <cl@linux.com> wrote:

> On Thu, 22 Apr 2010, Mel Gorman wrote:
>
> > vma_adjust() is updating anon VMA information without any locks taken.
> > In constract, file-backed mappings use the i_mmap_lock. This lack of
> > locking can result in races with page migration. During rmap_walk(),
> > vma_address() can return -EFAULT for an address that will soon be valid.
> > This leaves a dangling migration PTE behind which can later cause a
> > BUG_ON to trigger when the page is faulted in.
>
> Isnt this also a race with reclaim / swap?
>
Yes, it's also race in reclaim/swap ...
page_referenced()
try_to_unmap().
rmap_walk() <==== we hit this case.

But above 2 are not considered to be critical.

I'm not sure how this race affect KSM.

Thanks,
-Kame



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