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.

Link: http://lkml.kernel.org/r/20190603143451.27353-4-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 6 insertions, 38 deletions

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index a35ab6c55192..82b6a20898bd 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -12,7 +12,6 @@ config DEBUG_PAGEALLOC
 	bool "Debug page memory allocations"
 	depends on DEBUG_KERNEL
 	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
-	select PAGE_EXTENSION
 	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	---help---
 	  Unmap pages from the kernel linear mapping after free_pages().
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 26b6ad8b065d..ae56e8feec0c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -50,7 +50,6 @@
 #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>
@@ -668,18 +667,6 @@ static int __init early_debug_pagealloc(char *buf)
 }
 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())
@@ -691,11 +678,6 @@ static void init_debug_guardpage(void)
 	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;
@@ -713,20 +695,13 @@ early_param("debug_guardpage_minorder", debug_guardpage_minorder_setup);
 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);
-	if (unlikely(!page_ext))
-		return false;
-
-	__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
-
+	__SetPageGuard(page);
 	INIT_LIST_HEAD(&page->lru);
 	set_page_private(page, order);
 	/* Guard pages are not available for any usage */
@@ -738,23 +713,16 @@ static inline bool set_page_guard(struct zone *zone, struct page *page,
 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);
-	if (unlikely(!page_ext))
-		return;
-
-	__clear_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
+	__ClearPageGuard(page);
 
 	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,
@@ -1930,6 +1898,10 @@ void __init page_alloc_init_late(void)
 
 	for_each_populated_zone(zone)
 		set_zone_contiguous(zone);
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+	init_debug_guardpage();
+#endif
 }
 
 #ifdef CONFIG_CMA
diff --git a/mm/page_ext.c b/mm/page_ext.c
index d8f1aca4ad43..5f5769c7db3b 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -59,9 +59,6 @@
  */
 
 static struct page_ext_operations *page_ext_ops[] = {
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	&debug_guardpage_ops,
-#endif
 #ifdef CONFIG_PAGE_OWNER
 	&page_owner_ops,
 #endif