[RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE

["Huang, Ying" <ying.huang@intel.com>]

From: Huang Ying <ying.huang@intel.com>

Now !PageSwapBacked() is used as the flag for the pages freed lazily
via MADV_FREE.  This isn't obvious enough.  So Dave suggested to add a
new page flag for that to improve the code readability.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
---
 include/linux/page-flags.h | 25 +++++++++++++++++++++++++
 mm/rmap.c                  |  6 +++---
 mm/swap.c                  | 11 +++--------
 mm/vmscan.c                |  7 +++----
 4 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 49c2697046b9..759748fbcfad 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -498,6 +498,31 @@ static __always_inline int PageKsm(struct page *page)
 TESTPAGEFLAG_FALSE(Ksm)
 #endif
 
+/*
+ * For pages freed lazily via MADV_FREE.  lazyfree pages are clean
+ * anonymous pages.  They have SwapBacked flag cleared to distinguish
+ * with normal anonymous pages
+ */
+static __always_inline int PageLazyFree(struct page *page)
+{
+	page = compound_head(page);
+	return PageAnon(page) && !PageSwapBacked(page);
+}
+
+static __always_inline void SetPageLazyFree(struct page *page)
+{
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	VM_BUG_ON_PAGE(!PageAnon(page), page);
+	ClearPageSwapBacked(page);
+}
+
+static __always_inline void ClearPageLazyFree(struct page *page)
+{
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	VM_BUG_ON_PAGE(!PageAnon(page), page);
+	SetPageSwapBacked(page);
+}
+
 u64 stable_page_flags(struct page *page);
 
 static inline int PageUptodate(struct page *page)
diff --git a/mm/rmap.c b/mm/rmap.c
index 03c5b116d30e..1dcbb1771dd7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1598,7 +1598,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 			 * Store the swap location in the pte.
 			 * See handle_pte_fault() ...
 			 */
-			if (unlikely(PageSwapBacked(page) != PageSwapCache(page))) {
+			if (unlikely(PageLazyFree(page) == PageSwapCache(page))) {
 				WARN_ON_ONCE(1);
 				ret = false;
 				/* We have to invalidate as we cleared the pte */
@@ -1609,7 +1609,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 			}
 
 			/* MADV_FREE page check */
-			if (!PageSwapBacked(page)) {
+			if (PageLazyFree(page)) {
 				if (!PageDirty(page)) {
 					/* Invalidate as we cleared the pte */
 					mmu_notifier_invalidate_range(mm,
@@ -1623,7 +1623,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 				 * discarded. Remap the page to page table.
 				 */
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				SetPageSwapBacked(page);
+				ClearPageLazyFree(page);
 				ret = false;
 				page_vma_mapped_walk_done(&pvmw);
 				break;
diff --git a/mm/swap.c b/mm/swap.c
index f502a2155e85..bd5e40e14c94 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -564,7 +564,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
 static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
 			    void *arg)
 {
-	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
+	if (PageLRU(page) && PageAnon(page) && !PageLazyFree(page) &&
 	    !PageSwapCache(page) && !PageUnevictable(page)) {
 		bool active = PageActive(page);
 
@@ -572,12 +572,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
 				       LRU_INACTIVE_ANON + active);
 		ClearPageActive(page);
 		ClearPageReferenced(page);
-		/*
-		 * lazyfree pages are clean anonymous pages. They have
-		 * SwapBacked flag cleared to distinguish normal anonymous
-		 * pages
-		 */
-		ClearPageSwapBacked(page);
+		SetPageLazyFree(page);
 		add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);
 
 		__count_vm_events(PGLAZYFREE, hpage_nr_pages(page));
@@ -678,7 +673,7 @@ void deactivate_page(struct page *page)
  */
 void mark_page_lazyfree(struct page *page)
 {
-	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
+	if (PageLRU(page) && PageAnon(page) && !PageLazyFree(page) &&
 	    !PageSwapCache(page) && !PageUnevictable(page)) {
 		struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f14c8c6069a6..0aaee7052fb0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1043,8 +1043,7 @@ static void page_check_dirty_writeback(struct page *page,
 	 * Anonymous pages are not handled by flushers and must be written
 	 * from reclaim context. Do not stall reclaim based on them
 	 */
-	if (!page_is_file_cache(page) ||
-	    (PageAnon(page) && !PageSwapBacked(page))) {
+	if (!page_is_file_cache(page) || PageLazyFree(page)) {
 		*dirty = false;
 		*writeback = false;
 		return;
@@ -1235,7 +1234,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 * Try to allocate it some swap space here.
 		 * Lazyfree page could be freed directly
 		 */
-		if (PageAnon(page) && PageSwapBacked(page)) {
+		if (PageAnon(page) && !PageLazyFree(page)) {
 			if (!PageSwapCache(page)) {
 				if (!(sc->gfp_mask & __GFP_IO))
 					goto keep_locked;
@@ -1411,7 +1410,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			}
 		}
 
-		if (PageAnon(page) && !PageSwapBacked(page)) {
+		if (PageLazyFree(page)) {
 			/* follow __remove_mapping for reference */
 			if (!page_ref_freeze(page, 1))
 				goto keep_locked;
-- 
2.25.0