[PATCH 1/2] vfs: Add hooks for filesystem-specific prune_icache_sb

[Bob Peterson <rpeterso@redhat.com>]

This patch adds filesystem-specific callbacks for shrinking the
inode cache, prune_icache_sb. This is provided for filesystems in
which the default VFS prune_icache_sb needs to be delayed due to
filesystem locking requirements not met by vfs.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 Documentation/filesystems/vfs.txt | 15 +++++++++++++++
 fs/inode.c                        |  1 +
 fs/super.c                        |  5 ++++-
 include/linux/fs.h                |  3 +++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index c61a223..7cb4c5c 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -230,6 +230,7 @@ struct super_operations {
         ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
 	int (*nr_cached_objects)(struct super_block *);
 	void (*free_cached_objects)(struct super_block *, int);
+	long (*prune_icache_sb)(struct super_block *, struct shrink_control *);
 };
 
 All methods are called without any locks being held, unless otherwise
@@ -319,6 +320,20 @@ or bottom half).
 	implementations will cause holdoff problems due to large scan batch
 	sizes.
 
+  prune_icache_sb: called by the sb cache shrinking function for the file
+	filesystem to reduce the number of inodes from slab. This is done to
+	accomodate file systems that may not be able to immediately remove
+	inodes from cache, but must queue them to be removed ASAP.
+
+	This can happen in GFS2, for example, where evicting an inode
+	may require an inter-node lock (glock) which makes a call into DLM
+	(distributed lock manager), which may block for any number of reasons.
+	For example, it may block because a customer node needs to be fenced,
+	so the lock cannot be granted until the fencing is complete.
+	The fencing, in turn, may be blocked for other reasons, such as
+	memory allocations that caused the shrinker to be called in the first
+	place. Optional. If not set, the default vfs prune_icache_sb is called.
+
 Whoever sets up the inode is responsible for filling in the "i_op" field. This
 is a pointer to a "struct inode_operations" which describes the methods that
 can be performed on individual inodes.
diff --git a/fs/inode.c b/fs/inode.c
index 4ccbc21..82c10f3 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -771,6 +771,7 @@ long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 	dispose_list(&freeable);
 	return freed;
 }
+EXPORT_SYMBOL(prune_icache_sb);
 
 static void __wait_on_freeing_inode(struct inode *inode);
 /*
diff --git a/fs/super.c b/fs/super.c
index d78b984..8087903 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -98,7 +98,10 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	sc->nr_to_scan = dentries + 1;
 	freed = prune_dcache_sb(sb, sc);
 	sc->nr_to_scan = inodes + 1;
-	freed += prune_icache_sb(sb, sc);
+	if (sb->s_op->prune_icache_sb)
+		freed += sb->s_op->prune_icache_sb(sb, sc);
+	else
+		freed += prune_icache_sb(sb, sc);
 
 	if (fs_objects) {
 		sc->nr_to_scan = fs_objects + 1;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5f61431..96e6ae2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1797,6 +1797,8 @@ struct super_operations {
 				  struct shrink_control *);
 	long (*free_cached_objects)(struct super_block *,
 				    struct shrink_control *);
+	long (*prune_icache_sb)(struct super_block *sb,
+				struct shrink_control *sc);
 };
 
 /*
@@ -2714,6 +2716,7 @@ extern void lockdep_annotate_inode_mutex_key(struct inode *inode);
 static inline void lockdep_annotate_inode_mutex_key(struct inode *inode) { };
 #endif
 extern void unlock_new_inode(struct inode *);
+extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
 extern unsigned int get_next_ino(void);
 
 extern void __iget(struct inode * inode);
-- 
2.5.5