From 41d78ba55037468e6c86c53e3076d1a74841de39 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 14 Feb 2006 13:52:58 -0800 Subject: [PATCH] compound page: use page[1].lru If a compound page has its own put_page_testzero destructor (the only current example is free_huge_page), that is noted in page[1].mapping of the compound page. But that's rather a poor place to keep it: functions which call set_page_dirty_lock after get_user_pages (e.g. Infiniband's __ib_umem_release) ought to be checking first, otherwise set_page_dirty is liable to crash on what's not the address of a struct address_space. And now I'm about to make that worse: it turns out that every compound page needs a destructor, so we can no longer rely on hugetlb pages going their own special way, to avoid further problems of page->mapping reuse. For example, not many people know that: on 50% of i386 -Os builds, the first tail page of a compound page purports to be PageAnon (when its destructor has an odd address), which surprises page_add_file_rmap. Keep the compound page destructor in page[1].lru.next instead. And to free up the common pairing of mapping and index, also move compound page order from index to lru.prev. Slab reuses page->lru too: but if we ever need slab to use compound pages, it can easily stack its use above this. (akpm: decoded version of the above: the tail pages of a compound page now have ->mapping==NULL, so there's no need for the set_page_dirty[_lock]() caller to check that they're not compund pages before doing the dirty). Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'mm/hugetlb.c') diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 67f29516662a..508707704d2c 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -85,7 +85,7 @@ void free_huge_page(struct page *page) BUG_ON(page_count(page)); INIT_LIST_HEAD(&page->lru); - page[1].mapping = NULL; + page[1].lru.next = NULL; /* reset dtor */ spin_lock(&hugetlb_lock); enqueue_huge_page(page); @@ -105,7 +105,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma, unsigned long addr) } spin_unlock(&hugetlb_lock); set_page_count(page, 1); - page[1].mapping = (void *)free_huge_page; + page[1].lru.next = (void *)free_huge_page; /* set dtor */ for (i = 0; i < (HPAGE_SIZE/PAGE_SIZE); ++i) clear_user_highpage(&page[i], addr); return page; -- cgit v1.2.3