[PATCH v2 2/4] mm: Stop accounting shadow entries

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

We no longer need to keep track of how many shadow entries are
present in a mapping.  This saves a few writes to the inode and
memory barriers.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: Vishal Verma <vishal.l.verma@intel.com>
---
 mm/filemap.c    | 13 -------------
 mm/swap_state.c |  4 ----
 mm/truncate.c   |  1 -
 mm/workingset.c |  1 -
 4 files changed, 19 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index bd116f63263e..2e68116be4b0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -140,17 +140,6 @@ static void page_cache_delete(struct address_space *mapping,
 
 	page->mapping = NULL;
 	/* Leave page->index set: truncation lookup relies upon it */
-
-	if (shadow) {
-		mapping->nrexceptional += nr;
-		/*
-		 * Make sure the nrexceptional update is committed before
-		 * the nrpages update so that final truncate racing
-		 * with reclaim does not see both counters 0 at the
-		 * same time and miss a shadow entry.
-		 */
-		smp_wmb();
-	}
 	mapping->nrpages -= nr;
 }
 
@@ -883,8 +872,6 @@ noinline int __add_to_page_cache_locked(struct page *page,
 		if (xas_error(&xas))
 			goto unlock;
 
-		if (old)
-			mapping->nrexceptional--;
 		mapping->nrpages++;
 
 		/* hugetlb pages do not participate in page cache accounting */
diff --git a/mm/swap_state.c b/mm/swap_state.c
index ee465827420e..85aca8d63aeb 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -160,7 +160,6 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry,
 			xas_store(&xas, page);
 			xas_next(&xas);
 		}
-		address_space->nrexceptional -= nr_shadows;
 		address_space->nrpages += nr;
 		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 		ADD_CACHE_INFO(add_total, nr);
@@ -199,8 +198,6 @@ void __delete_from_swap_cache(struct page *page,
 		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);
@@ -301,7 +298,6 @@ void clear_shadow_from_swap_cache(int type, unsigned long begin,
 			xas_store(&xas, NULL);
 			nr_shadows++;
 		}
-		address_space->nrexceptional -= nr_shadows;
 		xa_unlock_irq(&address_space->i_pages);
 
 		/* search the next swapcache until we meet end */
diff --git a/mm/truncate.c b/mm/truncate.c
index 58524aaf67e2..27cf411ae51f 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -40,7 +40,6 @@ static inline void __clear_shadow_entry(struct address_space *mapping,
 	if (xas_load(&xas) != entry)
 		return;
 	xas_store(&xas, NULL);
-	mapping->nrexceptional--;
 }
 
 static void clear_shadow_entry(struct address_space *mapping, pgoff_t index,
diff --git a/mm/workingset.c b/mm/workingset.c
index 975a4d2dd02e..74d5f460e446 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -557,7 +557,6 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 		goto out_invalid;
 	if (WARN_ON_ONCE(node->count != node->nr_values))
 		goto out_invalid;
-	mapping->nrexceptional -= node->nr_values;
 	xa_delete_node(node, workingset_update_node);
 	__inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
 
-- 
2.28.0