From 2668db9111bb1a6ab5a54f41f703179f35c7d098 Mon Sep 17 00:00:00 2001 From: Adam Litke Date: Mon, 10 Mar 2008 11:43:50 -0700 Subject: 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 Cc: Mel Gorman Cc: Dave Hansen Cc: William Lee Irwin III Cc: Andy Whitcroft Cc: Mel Gorman Cc: David Gibson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dcacc811e70e..74c1b6b0b37b 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); } } -- cgit v1.2.2