[patch 5/9] mm + fs: store shadow entries in page cache

[Johannes Weiner]

Reclaim will be leaving shadow entries in the page cache radix tree
upon evicting the real page.  As those pages are found from the LRU,
an iput() can lead to the inode being freed concurrently.  At this
point, reclaim must no longer install shadow pages because the inode
freeing code needs to ensure the page tree is really empty.

Add an address_space flag, AS_EXITING, that the inode freeing code
sets under the tree lock before doing the final truncate.  Reclaim
will check for this flag before installing shadow pages.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 fs/block_dev.c          |  2 +-
 fs/inode.c              |  7 ++++++-
 fs/nilfs2/inode.c       |  4 ++--
 include/linux/fs.h      |  1 +
 include/linux/pagemap.h | 13 ++++++++++++-
 mm/filemap.c            | 16 ++++++++++++----
 mm/truncate.c           |  5 +++--
 mm/vmscan.c             |  2 +-
 8 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c7bda5c..26b992d14 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -83,7 +83,7 @@ void kill_bdev(struct block_device *bdev)
 {
 	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
-	if (mapping->nrpages == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
 		return;
 
 	invalidate_bh_lrus();
diff --git a/fs/inode.c b/fs/inode.c
index e315c0a..8862b1b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -503,6 +503,7 @@ void clear_inode(struct inode *inode)
 	 */
 	spin_lock_irq(&inode->i_data.tree_lock);
 	BUG_ON(inode->i_data.nrpages);
+	BUG_ON(inode->i_data.nrshadows);
 	spin_unlock_irq(&inode->i_data.tree_lock);
 	BUG_ON(!list_empty(&inode->i_data.private_list));
 	BUG_ON(!(inode->i_state & I_FREEING));
@@ -545,10 +546,14 @@ static void evict(struct inode *inode)
 	 */
 	inode_wait_for_writeback(inode);
 
+	spin_lock_irq(&inode->i_data.tree_lock);
+	mapping_set_exiting(&inode->i_data);
+	spin_unlock_irq(&inode->i_data.tree_lock);
+
 	if (op->evict_inode) {
 		op->evict_inode(inode);
 	} else {
-		if (inode->i_data.nrpages)
+		if (inode->i_data.nrpages || inode->i_data.nrshadows)
 			truncate_inode_pages(&inode->i_data, 0);
 		clear_inode(inode);
 	}
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index b1a5277..047bafb 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -783,7 +783,7 @@ void nilfs_evict_inode(struct inode *inode)
 	int ret;
 
 	if (inode->i_nlink || !ii->i_root || unlikely(is_bad_inode(inode))) {
-		if (inode->i_data.nrpages)
+		if (inode->i_data.nrpages || inode->i_data.nrshadows)
 			truncate_inode_pages(&inode->i_data, 0);
 		clear_inode(inode);
 		nilfs_clear_inode(inode);
@@ -791,7 +791,7 @@ void nilfs_evict_inode(struct inode *inode)
 	}
 	nilfs_transaction_begin(sb, &ti, 0); /* never fails */
 
-	if (inode->i_data.nrpages)
+	if (inode->i_data.nrpages || inode->i_data.nrshadows)
 		truncate_inode_pages(&inode->i_data, 0);
 
 	/* TODO: some of the following operations may fail.  */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b09ddc0..ac5d84e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -416,6 +416,7 @@ struct address_space {
 	struct mutex		i_mmap_mutex;	/* protect tree, count, list */
 	/* Protected by tree_lock together with the radix tree */
 	unsigned long		nrpages;	/* number of total pages */
+	unsigned long		nrshadows;	/* number of shadow entries */
 	pgoff_t			writeback_index;/* writeback starts here */
 	const struct address_space_operations *a_ops;	/* methods */
 	unsigned long		flags;		/* error bits/gfp mask */
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index b6854b7..db3a78b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -25,6 +25,7 @@ enum mapping_flags {
 	AS_MM_ALL_LOCKS	= __GFP_BITS_SHIFT + 2,	/* under mm_take_all_locks() */
 	AS_UNEVICTABLE	= __GFP_BITS_SHIFT + 3,	/* e.g., ramdisk, SHM_LOCK */
 	AS_BALLOON_MAP  = __GFP_BITS_SHIFT + 4, /* balloon page special map */
+	AS_EXITING	= __GFP_BITS_SHIFT + 5, /* inode is being evicted */
 };
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -69,6 +70,16 @@ static inline int mapping_balloon(struct address_space *mapping)
 	return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
 }
 
+static inline void mapping_set_exiting(struct address_space *mapping)
+{
+	set_bit(AS_EXITING, &mapping->flags);
+}
+
+static inline int mapping_exiting(struct address_space *mapping)
+{
+	return test_bit(AS_EXITING, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
 	return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
@@ -547,7 +558,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
 				pgoff_t index, gfp_t gfp_mask);
 extern void delete_from_page_cache(struct page *page);
-extern void __delete_from_page_cache(struct page *page);
+extern void __delete_from_page_cache(struct page *page, void *shadow);
 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index 254eb16..34b2f0b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -112,7 +112,7 @@
  * sure the page is locked and that nobody else uses it - or that usage
  * is safe.  The caller must hold the mapping's tree_lock.
  */
-void __delete_from_page_cache(struct page *page)
+void __delete_from_page_cache(struct page *page, void *shadow)
 {
 	struct address_space *mapping = page->mapping;
 
@@ -127,7 +127,14 @@ void __delete_from_page_cache(struct page *page)
 	else
 		cleancache_invalidate_page(mapping, page);
 
-	radix_tree_delete(&mapping->page_tree, page->index);
+	if (shadow) {
+		void **slot;
+
+		slot = radix_tree_lookup_slot(&mapping->page_tree, page->index);
+		radix_tree_replace_slot(slot, shadow);
+		mapping->nrshadows++;
+	} else
+		radix_tree_delete(&mapping->page_tree, page->index);
 	page->mapping = NULL;
 	/* Leave page->index set: truncation lookup relies upon it */
 	mapping->nrpages--;
@@ -166,7 +173,7 @@ void delete_from_page_cache(struct page *page)
 
 	freepage = mapping->a_ops->freepage;
 	spin_lock_irq(&mapping->tree_lock);
-	__delete_from_page_cache(page);
+	__delete_from_page_cache(page, NULL);
 	spin_unlock_irq(&mapping->tree_lock);
 	mem_cgroup_uncharge_cache_page(page);
 
@@ -426,7 +433,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
 		new->index = offset;
 
 		spin_lock_irq(&mapping->tree_lock);
-		__delete_from_page_cache(old);
+		__delete_from_page_cache(old, NULL);
 		error = radix_tree_insert(&mapping->page_tree, offset, new);
 		BUG_ON(error);
 		mapping->nrpages++;
@@ -459,6 +466,7 @@ static int page_cache_insert(struct address_space *mapping, pgoff_t offset,
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 		radix_tree_replace_slot(slot, page);
+		mapping->nrshadows--;
 		return 0;
 	}
 	return radix_tree_insert(&mapping->page_tree, offset, page);
diff --git a/mm/truncate.c b/mm/truncate.c
index 21e4851..5c85dd4 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -35,7 +35,8 @@ static void clear_exceptional_entry(struct address_space *mapping,
 	 * without the tree itself locked.  These unlocked entries
 	 * need verification under the tree lock.
 	 */
-	radix_tree_delete_item(&mapping->page_tree, index, page);
+	if (radix_tree_delete_item(&mapping->page_tree, index, page) == page)
+		mapping->nrshadows--;
 	spin_unlock_irq(&mapping->tree_lock);
 }
 
@@ -481,7 +482,7 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
 		goto failed;
 
 	BUG_ON(page_has_private(page));
-	__delete_from_page_cache(page);
+	__delete_from_page_cache(page, NULL);
 	spin_unlock_irq(&mapping->tree_lock);
 	mem_cgroup_uncharge_cache_page(page);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a3bf7fd..dd5f67c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -545,7 +545,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
 
 		freepage = mapping->a_ops->freepage;
 
-		__delete_from_page_cache(page);
+		__delete_from_page_cache(page, NULL);
 		spin_unlock_irq(&mapping->tree_lock);
 		mem_cgroup_uncharge_cache_page(page);
 
-- 
1.8.3.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/