Re: [PATCH 04/14] mm,migration: Allow the migration ofPageSwapCache pages

[KAMEZAWA Hiroyuki]

On Thu, 22 Apr 2010 14:40:46 -0500 (CDT)
Christoph Lameter <cl@xxxxxxxxx> 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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