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>
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a2832c0..e92f047 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -82,9 +82,10 @@
#ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
#ifndef CONFIG_SPARSEMEM_VMEMMAP
-static void get_page_bootmem(unsigned long info, struct page *page, int type)
+static void get_page_bootmem(unsigned long info, struct page *page,
+ unsigned long type)
{
- atomic_set(&page->_mapcount, type);
+ page->lru.next = (struct list_head *) type;
SetPagePrivate(page);
set_page_private(page, info);
atomic_inc(&page->_count);
@@ -94,15 +95,16 @@
* so use __ref to tell modpost not to generate a warning */
void __ref put_page_bootmem(struct page *page)
{
- int type;
+ unsigned long type;
- type = atomic_read(&page->_mapcount);
- BUG_ON(type >= -1);
+ type = (unsigned long) page->lru.next;
+ BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
+ type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
if (atomic_dec_return(&page->_count) == 1) {
ClearPagePrivate(page);
set_page_private(page, 0);
- reset_page_mapcount(page);
+ INIT_LIST_HEAD(&page->lru);
__free_pages_bootmem(page, 0);
}