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authorHugh Dickins <hugh@veritas.com>2006-02-14 13:52:58 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-02-14 16:09:33 -0800
commit41d78ba55037468e6c86c53e3076d1a74841de39 (patch)
treed970f18d18532009b17c736583429401dbd64ade /mm/swap.c
parent7277232374680595cdbc774fd246b206f56db015 (diff)
downloadlwn-41d78ba55037468e6c86c53e3076d1a74841de39.tar.gz
lwn-41d78ba55037468e6c86c53e3076d1a74841de39.zip
[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 <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r--mm/swap.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 76247424dea1..cce3dda59c59 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -40,7 +40,7 @@ static void put_compound_page(struct page *page)
if (put_page_testzero(page)) {
void (*dtor)(struct page *page);
- dtor = (void (*)(struct page *))page[1].mapping;
+ dtor = (void (*)(struct page *))page[1].lru.next;
(*dtor)(page);
}
}