GFS2: Use RCU for glock hash table

This has a number of advantages:

 - Reduces contention on the hash table lock
 - Makes the code smaller and simpler
 - Should speed up glock dumps when under load
 - Removes ref count changing in examine_bucket
 - No longer need hash chain lock in glock_put() in common case

There are some further changes which this enables and which
we may do in the future. One is to look at using SLAB_RCU,
and another is to look at using a per-cpu counter for the
per-sb glock counter, since that is touched twice in the
lifetime of each glock (but only used at umount time).

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 3 insertions, 11 deletions

diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
index 6e493aee28f8..c80485cb6f25 100644
--- a/fs/gfs2/lock_dlm.c
+++ b/fs/gfs2/lock_dlm.c
@@ -22,7 +22,6 @@ static void gdlm_ast(void *arg)
 {
         struct gfs2_glock *gl = arg;
         unsigned ret = gl->gl_state;
-        struct gfs2_sbd *sdp = gl->gl_sbd;
 
         BUG_ON(gl->gl_lksb.sb_flags & DLM_SBF_DEMOTED);
 
@@ -31,12 +30,7 @@ static void gdlm_ast(void *arg)
 
         switch (gl->gl_lksb.sb_status) {
         case -DLM_EUNLOCK: /* Unlocked, so glock can be freed */
-                if (gl->gl_ops->go_flags & GLOF_ASPACE)
-                        kmem_cache_free(gfs2_glock_aspace_cachep, gl);
-                else
-                        kmem_cache_free(gfs2_glock_cachep, gl);
-                if (atomic_dec_and_test(&sdp->sd_glock_disposal))
-                        wake_up(&sdp->sd_glock_wait);
+                call_rcu(&gl->gl_rcu, gfs2_glock_free);
                 return;
         case -DLM_ECANCEL: /* Cancel while getting lock */
                 ret |= LM_OUT_CANCELED;
@@ -164,16 +158,14 @@ static int gdlm_lock(struct gfs2_glock *gl, unsigned int req_state,
                         GDLM_STRNAME_BYTES - 1, 0, gdlm_ast, gl, gdlm_bast);
 }
 
-static void gdlm_put_lock(struct kmem_cache *cachep, struct gfs2_glock *gl)
+static void gdlm_put_lock(struct gfs2_glock *gl)
 {
         struct gfs2_sbd *sdp = gl->gl_sbd;
         struct lm_lockstruct *ls = &sdp->sd_lockstruct;
         int error;
 
         if (gl->gl_lksb.sb_lkid == 0) {
-                kmem_cache_free(cachep, gl);
-                if (atomic_dec_and_test(&sdp->sd_glock_disposal))
-                        wake_up(&sdp->sd_glock_wait);
+                call_rcu(&gl->gl_rcu, gfs2_glock_free);
                 return;
         }