mm, debug_pagealloc: use a page type instead of page_ext flag

When debug_pagealloc is enabled, we currently allocate the page_ext array to mark guard pages with the PAGE_EXT_DEBUG_GUARD flag. Now that we have the page_type field in struct page, we can use that instead, as guard pages are neither PageSlab nor mapped to userspace. This reduces memory overhead when debug_pagealloc is enabled and there are no other features requiring the page_ext array.

Vlastimil Babka committed 7 years ago

Commit 3972f6b1 parent 4462b327 files · +17 −54Browse files

Unified · Split

7 files

Documentation/admin-guide/kernel-parameters.txt +4 −6
include/linux/mm.h +1 −9
include/linux/page-flags.h +6 −0
include/linux/page_ext.h +0 −1
mm/Kconfig.debug +0 −1
mm/page_alloc.c +6 −34
mm/page_ext.c +0 −3

Documentation/admin-guide/kernel-parameters.txt+4−6

 			tracking down these problems.
 	debug_pagealloc=
-			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
+			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
-			parameter enables the feature at boot time. In
+			enables the feature at boot time. By default, it is
-			default, it is disabled. We can avoid allocating huge
+			disabled and the system will work mostly the same as a
-			chunk of memory for debug pagealloc if we don't enable
+			kernel built without CONFIG_DEBUG_PAGEALLOC.
-			it at boot time and the system will work mostly same
-			with the kernel built without CONFIG_DEBUG_PAGEALLOC.
 			on: enable the feature
 	debugpat	[X86] Enable PAT debugging

include/linux/mm.h+1−9

 				bool allow_pagefault);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
-extern struct page_ext_operations debug_guardpage_ops;
 #ifdef CONFIG_DEBUG_PAGEALLOC
 extern unsigned int _debug_guardpage_minorder;
 DECLARE_STATIC_KEY_FALSE(_debug_guardpage_enabled);
 static inline bool page_is_guard(struct page *page)
 {
-	struct page_ext *page_ext;
 	if (!debug_guardpage_enabled())
 		return false;
-	page_ext = lookup_page_ext(page);
+	return PageGuard(page);
-	if (unlikely(!page_ext))
-		return false;
-	return test_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
 }
 #else
 static inline unsigned int debug_guardpage_minorder(void) { return 0; }

include/linux/page-flags.h+6−0

 #define PG_offline	0x00000100
 #define PG_kmemcg	0x00000200
 #define PG_table	0x00000400
+#define PG_guard	0x00000800
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
  */
 PAGE_TYPE_OPS(Table, table)
+/*
+ * Marks guardpages used with debug_pagealloc.
+ */
+PAGE_TYPE_OPS(Guard, guard)
 extern bool is_free_buddy_page(struct page *page);
 __PAGEFLAG(Isolated, isolated, PF_ANY);

include/linux/page_ext.h+0−1

@@ -17,7 +17,6 @@ struct page_ext_operations { · 16 unmodified lines
17	#ifdef CONFIG_PAGE_EXTENSION	17	#ifdef CONFIG_PAGE_EXTENSION
18		18
19	enum page_ext_flags {	19	enum page_ext_flags {
20	PAGE_EXT_DEBUG_GUARD,
21	PAGE_EXT_OWNER,	20	PAGE_EXT_OWNER,
22	#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)	21	#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
23	PAGE_EXT_YOUNG,	22	PAGE_EXT_YOUNG,

mm/Kconfig.debug+0−1

@@ -12,7 +12,6 @@ config DEBUG_PAGEALLOC · 11 unmodified lines
12	bool "Debug page memory allocations"	12	bool "Debug page memory allocations"
13	depends on DEBUG_KERNEL	13	depends on DEBUG_KERNEL
14	depends on !HIBERNATION \|\| ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC	14	depends on !HIBERNATION \|\| ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
15	select PAGE_EXTENSION
16	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC	15	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
17	---help---	16	---help---
18	Unmap pages from the kernel linear mapping after free_pages().	17	Unmap pages from the kernel linear mapping after free_pages().

mm/page_alloc.c+6−34

 #include <linux/backing-dev.h>
 #include <linux/fault-inject.h>
 #include <linux/page-isolation.h>
-#include <linux/page_ext.h>
 #include <linux/debugobjects.h>
 #include <linux/kmemleak.h>
 #include <linux/compaction.h>
 }
 early_param("debug_pagealloc", early_debug_pagealloc);
-static bool need_debug_guardpage(void)
-{
-	/* If we don't use debug_pagealloc, we don't need guard page */
-	if (!debug_pagealloc_enabled())
-		return false;
-	if (!debug_guardpage_minorder())
-		return false;
-	return true;
-}
 static void init_debug_guardpage(void)
 {
 	if (!debug_pagealloc_enabled())
 	static_branch_enable(&_debug_guardpage_enabled);
 }
-struct page_ext_operations debug_guardpage_ops = {
-	.need = need_debug_guardpage,
-	.init = init_debug_guardpage,
-};
 static int __init debug_guardpage_minorder_setup(char *buf)
 {
 	unsigned long res;
 static inline bool set_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype)
 {
-	struct page_ext *page_ext;
 	if (!debug_guardpage_enabled())
 		return false;
 	if (order >= debug_guardpage_minorder())
 		return false;
-	page_ext = lookup_page_ext(page);
+	__SetPageGuard(page);
-	if (unlikely(!page_ext))
-		return false;
-	__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
 	INIT_LIST_HEAD(&page->lru);
 	set_page_private(page, order);
 	/* Guard pages are not available for any usage */
 static inline void clear_page_guard(struct zone *zone, struct page *page,
 				unsigned int order, int migratetype)
 {
-	struct page_ext *page_ext;
 	if (!debug_guardpage_enabled())
 		return;
-	page_ext = lookup_page_ext(page);
+	__ClearPageGuard(page);
-	if (unlikely(!page_ext))
-		return;
-	__clear_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
 	set_page_private(page, 0);
 	if (!is_migrate_isolate(migratetype))
 		__mod_zone_freepage_state(zone, (1 << order), migratetype);
 }
 #else
-struct page_ext_operations debug_guardpage_ops;
 static inline bool set_page_guard(struct zone *zone, struct page *page,
 			unsigned int order, int migratetype) { return false; }
 static inline void clear_page_guard(struct zone *zone, struct page *page,
 	for_each_populated_zone(zone)
 		set_zone_contiguous(zone);
+#ifdef CONFIG_DEBUG_PAGEALLOC
+	init_debug_guardpage();
+#endif
 }
 #ifdef CONFIG_CMA

mm/page_ext.c+0−3

  */
 static struct page_ext_operations *page_ext_ops[] = {
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	&debug_guardpage_ops,
-#endif
 #ifdef CONFIG_PAGE_OWNER
 	&page_owner_ops,
 #endif

mm, debug_pagealloc: use a page type instead of page_ext flag

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