Re: [PATCH 22 of 30] pmd_trans_huge migrate bugcheck

[Andrea Arcangeli <aarcange@redhat.com>]

On Thu, Jan 21, 2010 at 02:40:41PM -0600, Christoph Lameter wrote:
> On Thu, 21 Jan 2010, Andrea Arcangeli wrote:
> 
> > From: Andrea Arcangeli <aarcange@redhat.com>
> >
> > No pmd_trans_huge should ever materialize in migration ptes areas, because
> > try_to_unmap will split the hugepage before migration ptes are instantiated.
> 
> try_to_unmap? How do you isolate the hugepages from the LRU? If you do
> isolate the huge pages via a LRU and get a 2M page then the migration
> logic has to be modified to be aware that huge pages may split during try_to_unmap.

Good point, all we need to do is to add one split_huge_page before
isolate_lru_page, the one in try_to_unmap isn't enough. Effectively I
guess I can remove the one in try_to_unmap then and replace it with
BUG_ON(TransHugePage(page)).

Subject: pmd_trans_huge migrate

From: Andrea Arcangeli <aarcange@redhat.com>

No pmd_trans_huge should ever materialize in migration ptes areas, because
we split the hugepage before migration ptes are instantiated.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/migrate.c b/mm/migrate.c
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -99,6 +99,7 @@ static int remove_migration_pte(struct p
 		goto out;
 
 	pmd = pmd_offset(pud, addr);
+	VM_BUG_ON(pmd_trans_huge(*pmd));
 	if (!pmd_present(*pmd))
 		goto out;
 
@@ -833,6 +834,9 @@ static int do_move_page_to_node_array(st
 				!migrate_all)
 			goto put_and_set;
 
+		if (unlikely(PageTransHuge(page)))
+			if (unlikely(split_huge_page(page)))
+				goto put_and_set;
 		err = isolate_lru_page(page);
 		if (!err) {
 			list_add_tail(&page->lru, &pagelist);

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