thp: remove PG_buddy

PG_buddy can be converted to _mapcount == -2.  So the PG_compound_lock can
be added to page->flags without overflowing (because of the sparse section
bits increasing) with CONFIG_X86_PAE=y and CONFIG_X86_PAT=y.  This also
has to move the memory hotplug code from _mapcount to lru.next to avoid
any risk of clashes.  We can't use lru.next for PG_buddy removal, but
memory hotplug can use lru.next even more easily than the mapcount
instead.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/sparse.c b/mm/sparse.c
index 95ac219..9325020 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -671,10 +671,10 @@ static void __kfree_section_memmap(struct page *memmap, unsigned long nr_pages)
 static void free_map_bootmem(struct page *page, unsigned long nr_pages)
 {
 	unsigned long maps_section_nr, removing_section_nr, i;
-	int magic;
+	unsigned long magic;
 
 	for (i = 0; i < nr_pages; i++, page++) {
-		magic = atomic_read(&page->_mapcount);
+		magic = (unsigned long) page->lru.next;
 
 		BUG_ON(magic == NODE_INFO);