[PATCH v2 2/8] mm/page_alloc: correct to clear guard attribute in DEBUG_PAGEALLOC

[Joonsoo Kim]

In __free_one_page(), we check the buddy page if it is guard page.
And, if so, we should clear guard attribute on the buddy page. But,
currently, we clear original page's order rather than buddy one's.
This doesn't have any problem, because resetting buddy's order
is useless and the original page's order is re-assigned soon.
But, it is better to correct code.

Additionally, I change (set/clear)_page_guard_flag() to
(set/clear)_page_guard() and makes these functions do all works
needed for guard page. This may make code more understandable.

One more thing, I did in this patch, is that fixing freepage accounting.
If we clear guard page and link it onto isolate buddy list, we should
not increase freepage count.

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/page_alloc.c |   29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 44672dc..3e1e344 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -441,18 +441,28 @@ static int __init debug_guardpage_minorder_setup(char *buf)
 }
 __setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
 
-static inline void set_page_guard_flag(struct page *page)
+static inline void set_page_guard(struct zone *zone, struct page *page,
+				unsigned int order, int migratetype)
 {
 	__set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+	set_page_private(page, order);
+	/* Guard pages are not available for any usage */
+	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
 }
 
-static inline void clear_page_guard_flag(struct page *page)
+static inline void clear_page_guard(struct zone *zone, struct page *page,
+				unsigned int order, int migratetype)
 {
 	__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
+	set_page_private(page, 0);
+	if (!is_migrate_isolate(migratetype))
+		__mod_zone_freepage_state(zone, (1 << order), migratetype);
 }
 #else
-static inline void set_page_guard_flag(struct page *page) { }
-static inline void clear_page_guard_flag(struct page *page) { }
+static inline void set_page_guard(struct zone *zone, struct page *page,
+				unsigned int order, int migratetype) {}
+static inline void clear_page_guard(struct zone *zone, struct page *page,
+				unsigned int order, int migratetype) {}
 #endif
 
 static inline void set_page_order(struct page *page, unsigned int order)
@@ -594,10 +604,7 @@ static inline void __free_one_page(struct page *page,
 		 * merge with it and move up one order.
 		 */
 		if (page_is_guard(buddy)) {
-			clear_page_guard_flag(buddy);
-			set_page_private(page, 0);
-			__mod_zone_freepage_state(zone, 1 << order,
-						  migratetype);
+			clear_page_guard(zone, buddy, order, migratetype);
 		} else {
 			list_del(&buddy->lru);
 			zone->free_area[order].nr_free--;
@@ -876,11 +883,7 @@ static inline void expand(struct zone *zone, struct page *page,
 			 * pages will stay not present in virtual address space
 			 */
 			INIT_LIST_HEAD(&page[size].lru);
-			set_page_guard_flag(&page[size]);
-			set_page_private(&page[size], high);
-			/* Guard pages are not available for any usage */
-			__mod_zone_freepage_state(zone, -(1 << high),
-						  migratetype);
+			set_page_guard(zone, &page[size], high, migratetype);
 			continue;
 		}
 #endif
-- 
1.7.9.5

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