[PATCH 4/9] mm/swapcache: support to handle the value in swapcache

[js1304@xxxxxxxxx]

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

Swapcache doesn't handle the value since there is no case using the value.
In the following patch, workingset detection for anonymous page will be
implemented and it stores the value into the swapcache. So, we need to
handle it and this patch implement handling.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 include/linux/swap.h |  5 +++--
 mm/swap_state.c      | 23 ++++++++++++++++++++---
 mm/vmscan.c          |  2 +-
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 954e13e..0df8b3f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -410,7 +410,8 @@ extern void show_swap_cache_info(void);
 extern int add_to_swap(struct page *page);
 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
 extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
-extern void __delete_from_swap_cache(struct page *, swp_entry_t entry);
+extern void __delete_from_swap_cache(struct page *page,
+			swp_entry_t entry, void *shadow);
 extern void delete_from_swap_cache(struct page *);
 extern void free_page_and_swap_cache(struct page *);
 extern void free_pages_and_swap_cache(struct page **, int);
@@ -571,7 +572,7 @@ static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
 }
 
 static inline void __delete_from_swap_cache(struct page *page,
-							swp_entry_t entry)
+					swp_entry_t entry, void *shadow)
 {
 }
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8e7ce9a..3fbbe45 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -117,6 +117,10 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
 	pgoff_t idx = swp_offset(entry);
 	XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
 	unsigned long i, nr = compound_nr(page);
+	unsigned long nrexceptional = 0;
+	void *old;
+
+	xas_set_update(&xas, workingset_update_node);
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageSwapCache(page), page);
@@ -132,10 +136,14 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
 			goto unlock;
 		for (i = 0; i < nr; i++) {
 			VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
+			old = xas_load(&xas);
+			if (xa_is_value(old))
+				nrexceptional++;
 			set_page_private(page + i, entry.val + i);
 			xas_store(&xas, page);
 			xas_next(&xas);
 		}
+		address_space->nrexceptional -= nrexceptional;
 		address_space->nrpages += nr;
 		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 		ADD_CACHE_INFO(add_total, nr);
@@ -155,24 +163,33 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
  * This must be called only on pages that have
  * been verified to be in the swap cache.
  */
-void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
+void __delete_from_swap_cache(struct page *page,
+			swp_entry_t entry, void *shadow)
 {
 	struct address_space *address_space = swap_address_space(entry);
 	int i, nr = hpage_nr_pages(page);
 	pgoff_t idx = swp_offset(entry);
 	XA_STATE(xas, &address_space->i_pages, idx);
 
+	/* Do not apply workingset detection for the hugh page */
+	if (nr > 1)
+		shadow = NULL;
+
+	xas_set_update(&xas, workingset_update_node);
+
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 	VM_BUG_ON_PAGE(PageWriteback(page), page);
 
 	for (i = 0; i < nr; i++) {
-		void *entry = xas_store(&xas, NULL);
+		void *entry = xas_store(&xas, shadow);
 		VM_BUG_ON_PAGE(entry != page, entry);
 		set_page_private(page + i, 0);
 		xas_next(&xas);
 	}
 	ClearPageSwapCache(page);
+	if (shadow)
+		address_space->nrexceptional += nr;
 	address_space->nrpages -= nr;
 	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
 	ADD_CACHE_INFO(del_total, nr);
@@ -247,7 +264,7 @@ void delete_from_swap_cache(struct page *page)
 	struct address_space *address_space = swap_address_space(entry);
 
 	xa_lock_irq(&address_space->i_pages);
-	__delete_from_swap_cache(page, entry);
+	__delete_from_swap_cache(page, entry, NULL);
 	xa_unlock_irq(&address_space->i_pages);
 
 	put_swap_page(page, entry);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 74c3ade..99588ba 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -909,7 +909,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 	if (PageSwapCache(page)) {
 		swp_entry_t swap = { .val = page_private(page) };
 		mem_cgroup_swapout(page, swap);
-		__delete_from_swap_cache(page, swap);
+		__delete_from_swap_cache(page, swap, NULL);
 		xa_unlock_irqrestore(&mapping->i_pages, flags);
 		put_swap_page(page, swap);
 	} else {
-- 
2.7.4