Call the filesystem back whenever a page is removed from the page cache

NFS needs to be able to release objects that are stored in the page
cache once the page itself is no longer visible from the page cache.

This patch adds a callback to the address space operations that allows
filesystems to perform page cleanups once the page has been removed
from the page cache.

Original patch by: Linus Torvalds <torvalds@linux-foundation.org>
[trondmy: cover the cases of invalidate_inode_pages2() and
          truncate_inode_pages()]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

3 files changed, 16 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index ea89840..6b9aee2 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -143,13 +143,18 @@ void __remove_from_page_cache(struct page *page)
 void remove_from_page_cache(struct page *page)
 {
 	struct address_space *mapping = page->mapping;
+	void (*freepage)(struct page *);
 
 	BUG_ON(!PageLocked(page));
 
+	freepage = mapping->a_ops->freepage;
 	spin_lock_irq(&mapping->tree_lock);
 	__remove_from_page_cache(page);
 	spin_unlock_irq(&mapping->tree_lock);
 	mem_cgroup_uncharge_cache_page(page);
+
+	if (freepage)
+		freepage(page);
 }
 EXPORT_SYMBOL(remove_from_page_cache);
 
diff --git a/mm/truncate.c b/mm/truncate.c
index ba887bf..3c2d5dd 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -390,6 +390,10 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
 	__remove_from_page_cache(page);
 	spin_unlock_irq(&mapping->tree_lock);
 	mem_cgroup_uncharge_cache_page(page);
+
+	if (mapping->a_ops->freepage)
+		mapping->a_ops->freepage(page);
+
 	page_cache_release(page);	/* pagecache ref */
 	return 1;
 failed:
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d31d7ce..9ca587c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -494,9 +494,16 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
 		spin_unlock_irq(&mapping->tree_lock);
 		swapcache_free(swap, page);
 	} else {
+		void (*freepage)(struct page *);
+
+		freepage = mapping->a_ops->freepage;
+
 		__remove_from_page_cache(page);
 		spin_unlock_irq(&mapping->tree_lock);
 		mem_cgroup_uncharge_cache_page(page);
+
+		if (freepage != NULL)
+			freepage(page);
 	}
 
 	return 1;