[PATCH 1/4] mm: Introduce and use page_cache_empty

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Instead of checking the two counters (nrpages and nrexceptional), we
can just check whether i_pages is empty.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/block_dev.c          |  2 +-
 fs/dax.c                |  2 +-
 include/linux/pagemap.h |  5 +++++
 mm/truncate.c           | 18 +++---------------
 4 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 0ae656e022fd..2a77bd2c6144 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -79,7 +79,7 @@ static void kill_bdev(struct block_device *bdev)
 {
 	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
-	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
+	if (page_cache_empty(mapping))
 		return;
 
 	invalidate_bh_lrus();
diff --git a/fs/dax.c b/fs/dax.c
index 11b16729b86f..2f75ee2cd41f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -949,7 +949,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
 		return -EIO;
 
-	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
+	if (page_cache_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL)
 		return 0;
 
 	trace_dax_writeback_range(inode, xas.xa_index, end_index);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 484a36185bb5..a474a92a2a72 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -18,6 +18,11 @@
 
 struct pagevec;
 
+static inline bool page_cache_empty(struct address_space *mapping)
+{
+	return xa_empty(&mapping->i_pages);
+}
+
 /*
  * Bits in mapping->flags.
  */
diff --git a/mm/truncate.c b/mm/truncate.c
index dd9ebc1da356..7c4c8ac140be 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -300,7 +300,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	pgoff_t		index;
 	int		i;
 
-	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
+	if (page_cache_empty(mapping))
 		goto out;
 
 	/* Offsets within partial pages */
@@ -488,9 +488,6 @@ EXPORT_SYMBOL(truncate_inode_pages);
  */
 void truncate_inode_pages_final(struct address_space *mapping)
 {
-	unsigned long nrexceptional;
-	unsigned long nrpages;
-
 	/*
 	 * Page reclaim can not participate in regular inode lifetime
 	 * management (can't call iput()) and thus can race with the
@@ -500,16 +497,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
 	 */
 	mapping_set_exiting(mapping);
 
-	/*
-	 * When reclaim installs eviction entries, it increases
-	 * nrexceptional first, then decreases nrpages.  Make sure we see
-	 * this in the right order or we might miss an entry.
-	 */
-	nrpages = mapping->nrpages;
-	smp_rmb();
-	nrexceptional = mapping->nrexceptional;
-
-	if (nrpages || nrexceptional) {
+	if (!page_cache_empty(mapping)) {
 		/*
 		 * As truncation uses a lockless tree lookup, cycle
 		 * the tree lock to make sure any ongoing tree
@@ -692,7 +680,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 	int ret2 = 0;
 	int did_range_unmap = 0;
 
-	if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
+	if (page_cache_empty(mapping))
 		goto out;
 
 	pagevec_init(&pvec);
-- 
2.27.0