[RFCv3 2/5] mm/compaction: enable mobile-page migration

@@ -146,6 +146,9 @@ u64 stable_page_flags(struct page *page)
 	if (PageBalloon(page))
 		u |= 1 << KPF_BALLOON;
 
+	if (PageMobile(page))
+		u |= 1 << KPF_MOBILE;
+
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
 
 	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);

@@ -1,6 +1,9 @@
 #ifndef _LINUX_COMPACTION_H
 #define _LINUX_COMPACTION_H
 
+#include <linux/page-flags.h>
+#include <linux/pagemap.h>
+
 /* Return values for compact_zone() and try_to_compact_pages() */
 /* compaction didn't start as it was deferred due to past failures */
 #define COMPACT_DEFERRED	0

@@ -51,6 +54,66 @@ extern void compaction_defer_reset(struct zone *zone, int order,
 				bool alloc_success);
 extern bool compaction_restarting(struct zone *zone, int order);
 
+static inline bool mobile_page(struct page *page)
+{
+	return page->mapping &&	page->mapping->a_ops &&
+		(PageMobile(page) || PageBalloon(page));
+}
+
+static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
+{
+	bool ret;
+
+	/*
+	 * Avoid burning cycles with pages that are yet under __free_pages(),
+	 * or just got freed under us.
+	 *
+	 * In case we 'win' a race for a mobile page being freed under us and
+	 * raise its refcount preventing __free_pages() from doing its job
+	 * the put_page() at the end of this block will take care of
+	 * release this page, thus avoiding a nasty leakage.
+	 */
+	if (likely(get_page_unless_zero(page))) {
+		/*
+		 * As mobile pages are not isolated from LRU lists, concurrent
+		 * compaction threads can race against page migration functions
+		 * as well as race against the releasing a page.
+		 *
+		 * In order to avoid having an already isolated mobile page
+		 * being (wrongly) re-isolated while it is under migration,
+		 * or to avoid attempting to isolate pages being released,
+		 * lets be sure we have the page lock
+		 * before proceeding with the mobile page isolation steps.
+		 */
+		if (likely(trylock_page(page))) {
+			if (mobile_page(page) &&
+			    page->mapping->a_ops->isolatepage) {
+				ret = page->mapping->a_ops->isolatepage(page,
+									mode);
+				unlock_page(page);
+				return ret;
+			}
+			unlock_page(page);
+		}
+		put_page(page);
+	}
+	return false;
+}
+
+static inline void putback_mobilepage(struct page *page)
+{
+	/*
+	 * 'lock_page()' stabilizes the page and prevents races against
+	 * concurrent isolation threads attempting to re-isolate it.
+	 */
+	lock_page(page);
+	if (mobile_page(page) && page->mapping->a_ops->putbackpage) {
+		page->mapping->a_ops->putbackpage(page);
+		/* drop the extra ref count taken for mobile page isolation */
+		put_page(page);
+	}
+	unlock_page(page);
+}
 #else
 static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
 			unsigned int order, int alloc_flags,

@@ -83,6 +146,19 @@ static inline bool compaction_deferred(struct zone *zone, int order)
 	return true;
 }
 
+static inline bool mobile_page(struct page *page)
+{
+	return false;
+}
+
+static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
+{
+	return false;
+}
+
+static inline void putback_mobilepage(struct page *page)
+{
+}
 #endif /* CONFIG_COMPACTION */
 
 #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)

@@ -395,6 +395,8 @@ struct address_space_operations {
 	 */
 	int (*migratepage) (struct address_space *,
 			struct page *, struct page *, enum migrate_mode);
+	bool (*isolatepage) (struct page *, isolate_mode_t);
+	void (*putbackpage) (struct page *);
 	int (*launder_page) (struct page *);
 	int (*is_partially_uptodate) (struct page *, unsigned long,
 					unsigned long);

@@ -582,6 +582,25 @@ static inline void __ClearPageBalloon(struct page *page)
 	atomic_set(&page->_mapcount, -1);
 }
 
+#define PAGE_MOBILE_MAPCOUNT_VALUE (-255)
+
+static inline int PageMobile(struct page *page)
+{
+	return atomic_read(&page->_mapcount) == PAGE_MOBILE_MAPCOUNT_VALUE;
+}
+
+static inline void __SetPageMobile(struct page *page)
+{
+	VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
+	atomic_set(&page->_mapcount, PAGE_MOBILE_MAPCOUNT_VALUE);
+}
+
+static inline void __ClearPageMobile(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageMobile(page), page);
+	atomic_set(&page->_mapcount, -1);
+}
+
 /*
  * If network-based swap is enabled, sl*b must keep track of whether pages
  * were allocated from pfmemalloc reserves.

@@ -33,6 +33,7 @@
 #define KPF_THP			22
 #define KPF_BALLOON		23
 #define KPF_ZERO_PAGE		24
+#define KPF_MOBILE		25
 
 
 #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */