[PATCH 3/4] dcache set size

[Glauber Costa <glommer@parallels.com>]

Simple patch that provides a function allowing its caller to set
the maximum number of dentries that can exist at the same time
at a given super block. Will be used in a later patch.

Signed-off-by: Glauber Costa <glommer@parallels.com>
CC: Dave Chinner <david@fromorbit.com>
---
 fs/dcache.c            |   12 ++++++++++++
 include/linux/dcache.h |    1 +
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 3bdb106..4369aa2 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1202,6 +1202,18 @@ static int dcache_mem_check(struct super_block *sb)
 	return -ENOMEM;
 }
 
+int vfs_set_dcache_size(struct super_block *sb, int size)
+{
+	unsigned long dr = percpu_counter_sum_positive(&sb->s_nr_dentry); 
+
+	if (size != sb->s_nr_dentry_max)
+		prune_dcache_sb(sb, dr - size);
+
+	sb->s_nr_dentry_max = size;
+
+	return 0;
+}
+
 /**
  * __d_alloc	-	allocate a dcache entry
  * @sb: filesystem it will belong to
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index d37d2a7..cd1ab71 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -251,6 +251,7 @@ extern int d_invalidate(struct dentry *);
 
 /* only used at mount-time */
 extern struct dentry * d_alloc_root(struct inode *);
+extern int vfs_set_dcache_size(struct super_block *sb, int size);
 
 /* <clickety>-<click> the ramfs-type tree */
 extern void d_genocide(struct dentry *);
-- 
1.7.6