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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
commit 5f24ce5fd3
7 changed files with 52 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

14
include/linux/memory_hotplug.h
View file

@ -13,12 +13,16 @@ struct mem_section;
#ifdef CONFIG_MEMORY_HOTPLUG
/*
* Types for free bootmem.
* The normal smallest mapcount is -1. Here is smaller value than it.
* Types for free bootmem stored in page->lru.next. These have to be in
* some random range in unsigned long space for debugging purposes.
*/
#define SECTION_INFO (-1 - 1)
#define MIX_SECTION_INFO (-1 - 2)
#define NODE_INFO (-1 - 3)
enum {
MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 12,
SECTION_INFO = MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,
MIX_SECTION_INFO,
NODE_INFO,
MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE = NODE_INFO,
};
/*
* pgdat resizing functions

21
include/linux/mm.h
View file

@ -397,6 +397,27 @@ static inline void init_page_count(struct page *page)
atomic_set(&page->_count, 1);
}
/*
* PageBuddy() indicate that the page is free and in the buddy system
* (see mm/page_alloc.c).
*/
static inline int PageBuddy(struct page *page)
{
return atomic_read(&page->_mapcount) == -2;
}
static inline void __SetPageBuddy(struct page *page)
{
VM_BUG_ON(atomic_read(&page->_mapcount) != -1);
atomic_set(&page->_mapcount, -2);
}
static inline void __ClearPageBuddy(struct page *page)
{
VM_BUG_ON(!PageBuddy(page));
atomic_set(&page->_mapcount, -1);
}
void put_page(struct page *page);
void put_pages_list(struct list_head *pages);

7
include/linux/page-flags.h
View file

@ -48,9 +48,6 @@
* struct page (these bits with information) are always mapped into kernel
* address space...
*
* PG_buddy is set to indicate that the page is free and in the buddy system
* (see mm/page_alloc.c).
*
* PG_hwpoison indicates that a page got corrupted in hardware and contains
* data with incorrect ECC bits that triggered a machine check. Accessing is
* not safe since it may cause another machine check. Don't touch!
@ -96,7 +93,6 @@ enum pageflags {
PG_swapcache, /* Swap page: swp_entry_t in private */
PG_mappedtodisk, /* Has blocks allocated on-disk */
PG_reclaim, /* To be reclaimed asap */
PG_buddy, /* Page is free, on buddy lists */
PG_swapbacked, /* Page is backed by RAM/swap */
PG_unevictable, /* Page is "unevictable" */
#ifdef CONFIG_MMU
@ -233,7 +229,6 @@ PAGEFLAG(OwnerPriv1, owner_priv_1) TESTCLEARFLAG(OwnerPriv1, owner_priv_1)
* risky: they bypass page accounting.
*/
TESTPAGEFLAG(Writeback, writeback) TESTSCFLAG(Writeback, writeback)
__PAGEFLAG(Buddy, buddy)
PAGEFLAG(MappedToDisk, mappedtodisk)
/* PG_readahead is only used for file reads; PG_reclaim is only for writes */
@ -461,7 +456,7 @@ static inline int PageTransCompound(struct page *page)
#define PAGE_FLAGS_CHECK_AT_FREE \
(1 << PG_lru | 1 << PG_locked | \
1 << PG_private | 1 << PG_private_2 | \
1 << PG_buddy | 1 << PG_writeback | 1 << PG_reserved | \
1 << PG_writeback | 1 << PG_reserved | \
1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
__PG_COMPOUND_LOCK)