[PATCH v4 4/8] mm/swapcache: support to handle the exceptional entries in swapcache

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

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

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 include/linux/swap.h | 10 ++++++----
 mm/shmem.c           |  3 ++-
 mm/swap_state.c      | 26 ++++++++++++++++++++------
 mm/vmscan.c          |  2 +-
 4 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 954e13e..273de48 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -408,9 +408,11 @@ extern struct address_space *swapper_spaces[];
 extern unsigned long total_swapcache_pages(void);
 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,
+			gfp_t gfp, void **shadowp);
 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);
@@ -565,13 +567,13 @@ static inline int add_to_swap(struct page *page)
 }
 
 static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
-							gfp_t gfp_mask)
+					gfp_t gfp_mask, void **shadowp)
 {
 	return -1;
 }
 
 static inline void __delete_from_swap_cache(struct page *page,
-							swp_entry_t entry)
+					swp_entry_t entry, void *shadow)
 {
 }
 
diff --git a/mm/shmem.c b/mm/shmem.c
index 8793e8c..c6663ad 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1370,7 +1370,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 		list_add(&info->swaplist, &shmem_swaplist);
 
 	if (add_to_swap_cache(page, swap,
-			__GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN) == 0) {
+			__GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN,
+			NULL) == 0) {
 		spin_lock_irq(&info->lock);
 		shmem_recalc_inode(inode);
 		info->swapped++;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8e7ce9a..f06af84 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -111,12 +111,15 @@ void show_swap_cache_info(void)
  * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  * but sets SwapCache flag and private instead of mapping and index.
  */
-int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
+int add_to_swap_cache(struct page *page, swp_entry_t entry,
+			gfp_t gfp, void **shadowp)
 {
 	struct address_space *address_space = swap_address_space(entry);
 	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;
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageSwapCache(page), page);
@@ -132,10 +135,17 @@ 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++;
+				if (shadowp)
+					*shadowp = old;
+			}
 			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);
@@ -155,7 +165,8 @@ 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);
@@ -167,12 +178,14 @@ void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
 	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);
@@ -209,7 +222,7 @@ int add_to_swap(struct page *page)
 	 * Add it to the swap cache.
 	 */
 	err = add_to_swap_cache(page, entry,
-			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
+			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
 	if (err)
 		/*
 		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
@@ -247,7 +260,7 @@ 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);
@@ -418,7 +431,8 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		/* May fail (-ENOMEM) if XArray node allocation failed. */
 		__SetPageLocked(new_page);
 		__SetPageSwapBacked(new_page);
-		err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
+		err = add_to_swap_cache(new_page, entry,
+				gfp_mask & GFP_KERNEL, NULL);
 		if (likely(!err)) {
 			/* Initiate read into locked page */
 			SetPageWorkingset(new_page);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0493c25..9871861 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