Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 21 Apr 2010 16:00:38 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages |
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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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