CacheFiles: Provide read-and-reset release counters for cachefilesd

Provide read-and-reset objects- and blocks-released counters for cachefilesd
to use to work out whether there's anything new that can be culled.

One of the problems cachefilesd has is that if all the objects in the cache
are pinned by inodes lying dormant in the kernel inode cache, there isn't
anything for it to cull.  In such a case, it just spins around walking the
filesystem tree and scanning for something to cull.  This eats up a lot of
CPU time.

By telling cachefilesd if there have been any releases, the daemon can
sleep until there is the possibility of something to do.

cachefilesd finds this information by the following means:

 (1) When the control fd is read, the kernel presents a list of values of
     interest.  "freleased=N" and "breleased=N" are added to this list to
     indicate the number of files released and number of blocks released
     since the last read call.  At this point the counters are reset.

 (2) POLLIN is signalled if the number of files released becomes greater
     than 0.

Note that by 'released' it just means that the kernel has released its
interest in those files for the moment, not necessarily that the files
should be deleted from the cache.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 23 insertions, 5 deletions

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index 1c2334c163dd..4ae75006e73b 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -258,6 +258,28 @@ requeue:
 }
 
 /*
+ * Mark an object as being inactive.
+ */
+void cachefiles_mark_object_inactive(struct cachefiles_cache *cache,
+				     struct cachefiles_object *object)
+{
+	write_lock(&cache->active_lock);
+	rb_erase(&object->active_node, &cache->active_nodes);
+	clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
+	write_unlock(&cache->active_lock);
+
+	wake_up_bit(&object->flags, CACHEFILES_OBJECT_ACTIVE);
+
+	/* This object can now be culled, so we need to let the daemon know
+	 * that there is something it can remove if it needs to.
+	 */
+	atomic_long_add(d_backing_inode(object->dentry)->i_blocks,
+			&cache->b_released);
+	if (atomic_inc_return(&cache->f_released))
+		cachefiles_state_changed(cache);
+}
+
+/*
  * delete an object representation from the cache
  * - file backed objects are unlinked
  * - directory backed objects are stuffed into the graveyard for userspace to
@@ -684,11 +706,7 @@ mark_active_timed_out:
 
 check_error:
 	_debug("check error %d", ret);
-	write_lock(&cache->active_lock);
-	rb_erase(&object->active_node, &cache->active_nodes);
-	clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
-	wake_up_bit(&object->flags, CACHEFILES_OBJECT_ACTIVE);
-	write_unlock(&cache->active_lock);
+	cachefiles_mark_object_inactive(cache, object);
 release_dentry:
 	dput(object->dentry);
 	object->dentry = NULL;