fscache: Attach the index key and aux data to the cookie

Attach copies of the index key and auxiliary data to the fscache cookie so
that:

 (1) The callbacks to the netfs for this stuff can be eliminated.  This
     can simplify things in the cache as the information is still
     available, even after the cache has relinquished the cookie.

 (2) Simplifies the locking requirements of accessing the information as we
     don't have to worry about the netfs object going away on us.

 (3) The cache can do lazy updating of the coherency information on disk.
     As long as the cache is flushed before reboot/poweroff, there's no
     need to update the coherency info on disk every time it changes.

 (4) Cookies can be hashed or put in a tree as the index key is easily
     available.  This allows:

     (a) Checks for duplicate cookies can be made at the top fscache layer
     	 rather than down in the bowels of the cache backend.

     (b) Caching can be added to a netfs object that has a cookie if the
     	 cache is brought online after the netfs object is allocated.

A certain amount of space is made in the cookie for inline copies of the
data, but if it won't fit there, extra memory will be allocated for it.

The downside of this is that live cache operation requires more memory.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Anna Schumaker <anna.schumaker@netapp.com>
Tested-by: Steve Dickson <steved@redhat.com>

1 files changed, 18 insertions, 4 deletions

diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index 7c0ddb7ae29a..a7b28f876fde 100644
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -144,6 +144,7 @@ static void fscache_put_object(struct fscache_object *,
 			       enum fscache_obj_ref_trace);
 static bool fscache_enqueue_dependents(struct fscache_object *, int);
 static void fscache_dequeue_object(struct fscache_object *);
+static void fscache_update_aux_data(struct fscache_object *);
 
 /*
  * we need to notify the parent when an op completes that we had outstanding
@@ -711,6 +712,11 @@ static const struct fscache_state *fscache_drop_object(struct fscache_object *ob
 	ASSERT(cookie != NULL);
 	ASSERT(!hlist_unhashed(&object->cookie_link));
 
+	if (test_bit(FSCACHE_COOKIE_AUX_UPDATED, &cookie->flags)) {
+		_debug("final update");
+		fscache_update_aux_data(object);
+	}
+
 	/* Make sure the cookie no longer points here and that the netfs isn't
 	 * waiting for us.
 	 */
@@ -1037,6 +1043,17 @@ static const struct fscache_state *fscache_invalidate_object(struct fscache_obje
 }
 
 /*
+ * Update auxiliary data.
+ */
+static void fscache_update_aux_data(struct fscache_object *object)
+{
+	fscache_stat(&fscache_n_updates_run);
+	fscache_stat(&fscache_n_cop_update_object);
+	object->cache->ops->update_object(object);
+	fscache_stat_d(&fscache_n_cop_update_object);
+}
+
+/*
  * Asynchronously update an object.
  */
 static const struct fscache_state *fscache_update_object(struct fscache_object *object,
@@ -1044,10 +1061,7 @@ static const struct fscache_state *fscache_update_object(struct fscache_object *
 {
 	_enter("{OBJ%x},%d", object->debug_id, event);
 
-	fscache_stat(&fscache_n_updates_run);
-	fscache_stat(&fscache_n_cop_update_object);
-	object->cache->ops->update_object(object);
-	fscache_stat_d(&fscache_n_cop_update_object);
+	fscache_update_aux_data(object);
 
 	_leave("");
 	return transit_to(WAIT_FOR_CMD);