mm: introduce mapping AS_WORKINGSET flag

From: Konstantin Khlebnikov <khlebnikov@openvz.org>

This patch introduces new flag AS_WORKINGSET in mapping->flags.
If it set reclaimer will activates all pages for this inode after first usage.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 include/linux/pagemap.h |   16 ++++++++++++++++
 mm/vmscan.c             |   15 ++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cfaaa69..c15fc17 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -24,6 +24,7 @@ enum mapping_flags {
 	AS_ENOSPC	= __GFP_BITS_SHIFT + 1,	/* ENOSPC on async write */
 	AS_MM_ALL_LOCKS	= __GFP_BITS_SHIFT + 2,	/* under mm_take_all_locks() */
 	AS_UNEVICTABLE	= __GFP_BITS_SHIFT + 3,	/* e.g., ramdisk, SHM_LOCK */
+	AS_WORKINGSET	= __GFP_BITS_SHIFT + 4,	/* promote pages activation */
 };
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -53,6 +54,21 @@ static inline int mapping_unevictable(struct address_space *mapping)
 	return !!mapping;
 }
 
+static inline void mapping_set_workingset(struct address_space *mapping)
+{
+	set_bit(AS_WORKINGSET, &mapping->flags);
+}
+
+static inline void mapping_clear_workingset(struct address_space *mapping)
+{
+	clear_bit(AS_WORKINGSET, &mapping->flags);
+}
+
+static inline int mapping_test_workingset(struct address_space *mapping)
+{
+	return mapping && test_bit(AS_WORKINGSET, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
 	return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 57b9658..5ccbe8c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -701,6 +701,7 @@ enum page_references {
 };
 
 static enum page_references page_check_references(struct page *page,
+						  struct address_space *mapping,
 						  struct mem_cgroup_zone *mz,
 						  struct scan_control *sc)
 {
@@ -721,6 +722,13 @@ static enum page_references page_check_references(struct page *page,
 	if (vm_flags & VM_LOCKED)
 		return PAGEREF_RECLAIM;
 
+	/*
+	 * Activate workingset page if referenced at least once.
+	 */
+	if (mapping_test_workingset(mapping) &&
+	    (referenced_ptes || referenced_page))
+		return PAGEREF_ACTIVATE;
+
 	if (referenced_ptes) {
 		if (PageAnon(page))
 			return PAGEREF_ACTIVATE;
@@ -828,7 +836,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			}
 		}
 
-		references = page_check_references(page, mz, sc);
+		mapping = page_mapping(page);
+
+		references = page_check_references(page, mapping, mz, sc);
 		switch (references) {
 		case PAGEREF_ACTIVATE:
 			goto activate_locked;
@@ -848,11 +858,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				goto keep_locked;
 			if (!add_to_swap(page))
 				goto activate_locked;
+			mapping = &swapper_space;
 			may_enter_fs = 1;
 		}
 
-		mapping = page_mapping(page);
-
 		/*
 		 * The page is mapped into the page tables of one or more
 		 * processes. Try to unmap it here.