On Wed, Apr 21, 2010 at 09:30:20AM -0500, Christoph Lameter wrote:
> On Tue, 20 Apr 2010, Mel Gorman wrote:
>
> > @@ -520,10 +521,12 @@ static int move_to_new_page(struct page *newpage, struct page *page)
> > else
> > rc = fallback_migrate_page(mapping, newpage, page);
> >
> > - if (!rc)
> > - remove_migration_ptes(page, newpage);
> > - else
> > + if (rc) {
> > newpage->mapping = NULL;
> > + } else {
> > + if (remap_swapcache)
> > + remove_migration_ptes(page, newpage);
> > + }
>
> You are going to keep the migration ptes after the page has been unlocked?
Yes, because it's not known if the anon_vma for the unmapped swapcache page
still exists or not. Now, a bug has been reported where a migration PTE is
found where the page is not locked. I'm trying to determine if it's the same
page or not but the problem takes ages to reproduce.
> Or is remap_swapcache true if its not a swapcache page?
>
> Maybe you meant
>
> if (!remap_swapcache)
>
> ?
>
No, remap_swapcache could just be called "remap". If it's 0, it's
considered unsafe to remap the page.
> > unlock_page(newpage);
> >
>
> >
> > skip_unmap:
> > if (!page_mapped(page))
> > - rc = move_to_new_page(newpage, page);
> > + rc = move_to_new_page(newpage, page, remap_swapcache);
> >
> > - if (rc)
> > + if (rc && remap_swapcache)
> > remove_migration_ptes(page, page);
> > rcu_unlock:
> >
>
> Looks like you meant !remap_swapcache
>
If remap_swapcache is 1, the anon_vma is valid (or irrelevant because
it's a file) and it's safe to remap the page by removing the migration
PTEs.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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