From 9180706344487700b40da9eca5dedd3d11cb33b4 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Thu, 13 Jan 2011 15:46:32 -0800 Subject: thp: alter compound get_page/put_page Alter compound get_page/put_page to keep references on subpages too, in order to allow __split_huge_page_refcount to split an hugepage even while subpages have been pinned by one of the get_user_pages() variants. Signed-off-by: Andrea Arcangeli Acked-by: Rik van Riel Acked-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 83 insertions(+), 7 deletions(-) (limited to 'mm/swap.c') diff --git a/mm/swap.c b/mm/swap.c index 3f48542..33f5292 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -56,17 +56,93 @@ static void __page_cache_release(struct page *page) del_page_from_lru(zone, page); spin_unlock_irqrestore(&zone->lru_lock, flags); } +} + +static void __put_single_page(struct page *page) +{ + __page_cache_release(page); free_hot_cold_page(page, 0); } -static void put_compound_page(struct page *page) +static void __put_compound_page(struct page *page) { - page = compound_head(page); - if (put_page_testzero(page)) { - compound_page_dtor *dtor; + compound_page_dtor *dtor; + + __page_cache_release(page); + dtor = get_compound_page_dtor(page); + (*dtor)(page); +} - dtor = get_compound_page_dtor(page); - (*dtor)(page); +static void put_compound_page(struct page *page) +{ + if (unlikely(PageTail(page))) { + /* __split_huge_page_refcount can run under us */ + struct page *page_head = page->first_page; + smp_rmb(); + /* + * If PageTail is still set after smp_rmb() we can be sure + * that the page->first_page we read wasn't a dangling pointer. + * See __split_huge_page_refcount() smp_wmb(). + */ + if (likely(PageTail(page) && get_page_unless_zero(page_head))) { + unsigned long flags; + /* + * Verify that our page_head wasn't converted + * to a a regular page before we got a + * reference on it. + */ + if (unlikely(!PageHead(page_head))) { + /* PageHead is cleared after PageTail */ + smp_rmb(); + VM_BUG_ON(PageTail(page)); + goto out_put_head; + } + /* + * Only run compound_lock on a valid PageHead, + * after having it pinned with + * get_page_unless_zero() above. + */ + smp_mb(); + /* page_head wasn't a dangling pointer */ + flags = compound_lock_irqsave(page_head); + if (unlikely(!PageTail(page))) { + /* __split_huge_page_refcount run before us */ + compound_unlock_irqrestore(page_head, flags); + VM_BUG_ON(PageHead(page_head)); + out_put_head: + if (put_page_testzero(page_head)) + __put_single_page(page_head); + out_put_single: + if (put_page_testzero(page)) + __put_single_page(page); + return; + } + VM_BUG_ON(page_head != page->first_page); + /* + * We can release the refcount taken by + * get_page_unless_zero now that + * split_huge_page_refcount is blocked on the + * compound_lock. + */ + if (put_page_testzero(page_head)) + VM_BUG_ON(1); + /* __split_huge_page_refcount will wait now */ + VM_BUG_ON(atomic_read(&page->_count) <= 0); + atomic_dec(&page->_count); + VM_BUG_ON(atomic_read(&page_head->_count) <= 0); + compound_unlock_irqrestore(page_head, flags); + if (put_page_testzero(page_head)) + __put_compound_page(page_head); + } else { + /* page_head is a dangling pointer */ + VM_BUG_ON(PageTail(page)); + goto out_put_single; + } + } else if (put_page_testzero(page)) { + if (PageHead(page)) + __put_compound_page(page); + else + __put_single_page(page); } } @@ -75,7 +151,7 @@ void put_page(struct page *page) if (unlikely(PageCompound(page))) put_compound_page(page); else if (put_page_testzero(page)) - __page_cache_release(page); + __put_single_page(page); } EXPORT_SYMBOL(put_page); -- cgit v1.1