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authorAdam Litke <agl@us.ibm.com>2008-03-10 11:43:50 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-03-10 18:01:19 -0700
commit2668db9111bb1a6ab5a54f41f703179f35c7d098 (patch)
treebde940cfd298321663cf988b607151513c801a1a /mm/hugetlb.c
parent842078054da2d754c6b998b116d7c468abbfaaca (diff)
hugetlb: correct page count for surplus huge pages
Free pages in the hugetlb pool are free and as such have a reference count of zero. Regular allocations into the pool from the buddy are "freed" into the pool which results in their page_count dropping to zero. However, surplus pages can be directly utilized by the caller without first being freed to the pool. Therefore, a call to put_page_testzero() is in order so that such a page will be handed to the caller with a correct count. This has not affected end users because the bad page count is reset before the page is handed off. However, under CONFIG_DEBUG_VM this triggers a BUG when the page count is validated. Thanks go to Mel for first spotting this issue and providing an initial fix. Signed-off-by: Adam Litke <agl@us.ibm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Mel Gorman <mel@csn.ul.ie> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dcacc811e70..74c1b6b0b37 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -286,6 +286,12 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
spin_lock(&hugetlb_lock);
if (page) {
+ /*
+ * This page is now managed by the hugetlb allocator and has
+ * no users -- drop the buddy allocator's reference.
+ */
+ put_page_testzero(page);
+ VM_BUG_ON(page_count(page));
nid = page_to_nid(page);
set_compound_page_dtor(page, free_huge_page);
/*
@@ -369,13 +375,14 @@ free:
enqueue_huge_page(page);
else {
/*
- * Decrement the refcount and free the page using its
- * destructor. This must be done with hugetlb_lock
+ * The page has a reference count of zero already, so
+ * call free_huge_page directly instead of using
+ * put_page. This must be done with hugetlb_lock
* unlocked which is safe because free_huge_page takes
* hugetlb_lock before deciding how to free the page.
*/
spin_unlock(&hugetlb_lock);
- put_page(page);
+ free_huge_page(page);
spin_lock(&hugetlb_lock);
}
}