From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
PG_buddy can be converted to page->_count == -1. So the PG_compound_lock can be
added to page->flags without overflowing (because of the section bits
increasing) with CONFIG_X86_PAE=y.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
diff --git a/fs/proc/page.c b/fs/proc/page.c
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -116,15 +116,17 @@ u64 stable_page_flags(struct page *page)
if (PageHuge(page))
u |= 1 << KPF_HUGE;
+ /*
+ * Caveats on high order pages: page->_count will only be set
+ * -1 on the head page; SLUB/SLQB do the same for PG_slab;
+ * SLOB won't set PG_slab at all on compound pages.
+ */
+ if (PageBuddy(page))
+ u |= 1 << KPF_BUDDY;
+
u |= kpf_copy_bit(k, KPF_LOCKED, PG_locked);
- /*
- * Caveats on high order pages:
- * PG_buddy will only be set on the head page; SLUB/SLQB do the same
- * for PG_slab; SLOB won't set PG_slab at all on compound pages.
- */
u |= kpf_copy_bit(k, KPF_SLAB, PG_slab);
- u |= kpf_copy_bit(k, KPF_BUDDY, PG_buddy);
u |= kpf_copy_bit(k, KPF_ERROR, PG_error);
u |= kpf_copy_bit(k, KPF_DIRTY, PG_dirty);
diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -358,6 +358,27 @@ static inline void init_page_count(struc
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->_count) == -1;
+}
+
+static inline void __SetPageBuddy(struct page *page)
+{
+ VM_BUG_ON(atomic_read(&page->_count) != 0);
+ atomic_set(&page->_count, -1);
+}
+
+static inline void __ClearPageBuddy(struct page *page)
+{
+ VM_BUG_ON(!PageBuddy(page));
+ atomic_set(&page->_count, 0);
+}
+
void put_page(struct page *page);
void put_pages_list(struct list_head *pages);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -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
@@ -235,7 +231,6 @@ PAGEFLAG(OwnerPriv1, owner_priv_1) TESTC
* 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 */
@@ -430,7 +425,7 @@ static inline void ClearPageCompound(str
#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)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -426,8 +426,8 @@ __find_combined_index(unsigned long page
* (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 page->_count -1.
+ * Setting, clearing, and testing page->_count -1 is serialized by zone->lock.
*
* For recording page's order, we use page_private(page).
*/
@@ -440,10 +440,8 @@ static inline int page_is_buddy(struct p
if (page_zone_id(page) != page_zone_id(buddy))
return 0;
- if (PageBuddy(buddy) && page_order(buddy) == order) {
- VM_BUG_ON(page_count(buddy) != 0);
+ if (PageBuddy(buddy) && page_order(buddy) == order)
return 1;
- }
return 0;
}
@@ -460,7 +458,7 @@ static inline int page_is_buddy(struct p
* 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 page->count -1. 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
@@ -5251,7 +5249,6 @@ static struct trace_print_flags pageflag
{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
--
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