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thp: remove PG_buddy

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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>
This commit is contained in:
Andrea Arcangeli
2011-01-13 15:47:00 -08:00
committed by Linus Torvalds
parent 21ae5b0175
commit 5f24ce5fd3
7 changed files with 52 additions and 29 deletions
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7
mm/page_alloc.c
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@ -449,8 +449,8 @@ __find_combined_index(unsigned long page_idx, unsigned int order)
* (c) a page and its buddy have the same order &&
* (d) a page and its buddy are in the same zone.
*
* For recording whether a page is in the buddy system, we use PG_buddy.
* Setting, clearing, and testing PG_buddy is serialized by zone->lock.
* For recording whether a page is in the buddy system, we set ->_mapcount -2.
* Setting, clearing, and testing _mapcount -2 is serialized by zone->lock.
*
* For recording page's order, we use page_private(page).
*/
@ -483,7 +483,7 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
* as necessary, plus some accounting needed to play nicely with other
* parts of the VM system.
* At each level, we keep a list of pages, which are heads of continuous
* free pages of length of (1 << order) and marked with PG_buddy. Page's
* free pages of length of (1 << order) and marked with _mapcount -2. Page's
* order is recorded in page_private(page) field.
* So when we are allocating or freeing one, we can derive the state of the
* other. That is, if we allocate a small block, and both were
@ -5574,7 +5574,6 @@ static struct trace_print_flags pageflag_names[] = {
{1UL << PG_swapcache, "swapcache" },
{1UL << PG_mappedtodisk, "mappedtodisk" },
{1UL << PG_reclaim, "reclaim" },
{1UL << PG_buddy, "buddy" },
{1UL << PG_swapbacked, "swapbacked" },
{1UL << PG_unevictable, "unevictable" },
#ifdef CONFIG_MMU