gfs2: Replace gl_revokes with a GLF flag

The gl_revokes value determines how many outstanding revokes a glock has
on the superblock revokes list; this is used to avoid unnecessary log
flushes.  However, gl_revokes is only ever tested for being zero, and it's
only decremented in revoke_lo_after_commit, which removes all revokes
from the list, so we know that the gl_revoke values of all the glocks on
the list will reach zero.  Therefore, we can replace gl_revokes with a
bit flag. This saves an atomic counter in struct gfs2_glock.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

6 files changed, 31 insertions, 15 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 71c28ff98b56..15c605cfcfc8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -140,7 +140,7 @@ void gfs2_glock_free(struct gfs2_glock *gl)
 {
         struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
 
-        BUG_ON(atomic_read(&gl->gl_revokes));
+        BUG_ON(test_bit(GLF_REVOKES, &gl->gl_flags));
         rhashtable_remove_fast(&gl_hash_table, &gl->gl_node, ht_parms);
         smp_mb();
         wake_up_glock(gl);
@@ -1801,7 +1801,7 @@ void gfs2_dump_glock(struct seq_file *seq, struct gfs2_glock *gl)
                   state2str(gl->gl_target),
                   state2str(gl->gl_demote_state), dtime,
                   atomic_read(&gl->gl_ail_count),
-                  atomic_read(&gl->gl_revokes),
+                  test_bit(GLF_REVOKES, &gl->gl_flags) ? 1 : 0,
                   (int)gl->gl_lockref.count, gl->gl_hold_time);
 
         list_for_each_entry(gh, &gl->gl_holders, gh_list)
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 86840a70ee1a..6a94b094a904 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -345,6 +345,7 @@ enum {
         GLF_OBJECT                      = 14, /* Used only for tracing */
         GLF_BLOCKING                    = 15,
         GLF_INODE_CREATING              = 16, /* Inode creation occurring */
+        GLF_REVOKES                     = 17, /* Glock has revokes in queue */
 };
 
 struct gfs2_glock {
@@ -374,7 +375,6 @@ struct gfs2_glock {
         struct list_head gl_lru;
         struct list_head gl_ail_list;
         atomic_t gl_ail_count;
-        atomic_t gl_revokes;
         struct delayed_work gl_work;
         union {
                 /* For inode and iopen glocks only */
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 7ba94b66c91b..d55315a46ece 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -606,8 +606,10 @@ void gfs2_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
         gfs2_remove_from_ail(bd); /* drops ref on bh */
         bd->bd_bh = NULL;
         sdp->sd_log_num_revoke++;
-        if (atomic_inc_return(&gl->gl_revokes) == 1)
+        if (!test_bit(GLF_REVOKES, &gl->gl_flags)) {
+                set_bit(GLF_REVOKES, &gl->gl_flags);
                 gfs2_glock_hold(gl);
+        }
         set_bit(GLF_LFLUSH, &gl->gl_flags);
         list_add(&bd->bd_list, &sdp->sd_log_le_revoke);
 }
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index b4f0a6a3ba59..2fd61853ba63 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -662,19 +662,34 @@ static void revoke_lo_before_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 static void revoke_lo_after_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 {
         struct list_head *head = &sdp->sd_log_le_revoke;
-        struct gfs2_bufdata *bd;
-        struct gfs2_glock *gl;
+        struct gfs2_bufdata *bd, *tmp;
 
-        while (!list_empty(head)) {
-                bd = list_entry(head->next, struct gfs2_bufdata, bd_list);
-                list_del_init(&bd->bd_list);
-                gl = bd->bd_gl;
-                if (atomic_dec_return(&gl->gl_revokes) == 0) {
-                        clear_bit(GLF_LFLUSH, &gl->gl_flags);
-                        gfs2_glock_queue_put(gl);
+        /*
+         * Glocks can be referenced repeatedly on the revoke list, but the list
+         * only holds one reference.  All glocks on the list will have the
+         * GLF_REVOKES flag set initially.
+         */
+
+        list_for_each_entry_safe(bd, tmp, head, bd_list) {
+                struct gfs2_glock *gl = bd->bd_gl;
+
+                if (test_bit(GLF_REVOKES, &gl->gl_flags)) {
+                        /* Keep each glock on the list exactly once. */
+                        clear_bit(GLF_REVOKES, &gl->gl_flags);
+                        continue;
                 }
+                list_del(&bd->bd_list);
+                kmem_cache_free(gfs2_bufdata_cachep, bd);
+        }
+        list_for_each_entry_safe(bd, tmp, head, bd_list) {
+                struct gfs2_glock *gl = bd->bd_gl;
+
+                list_del(&bd->bd_list);
                 kmem_cache_free(gfs2_bufdata_cachep, bd);
+                clear_bit(GLF_LFLUSH, &gl->gl_flags);
+                gfs2_glock_queue_put(gl);
         }
+        /* the list is empty now */
 }
 
 static void revoke_lo_before_scan(struct gfs2_jdesc *jd,
diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c
index 136484ef35d3..c700738de1f7 100644
--- a/fs/gfs2/main.c
+++ b/fs/gfs2/main.c
@@ -59,7 +59,6 @@ static void gfs2_init_glock_once(void *foo)
         INIT_LIST_HEAD(&gl->gl_lru);
         INIT_LIST_HEAD(&gl->gl_ail_list);
         atomic_set(&gl->gl_ail_count, 0);
-        atomic_set(&gl->gl_revokes, 0);
 }
 
 static void gfs2_init_gl_aspace_once(void *foo)
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 7b8d2306b3d3..2a7692d70394 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1474,7 +1474,7 @@ static void gfs2_final_release_pages(struct gfs2_inode *ip)
         truncate_inode_pages(gfs2_glock2aspace(ip->i_gl), 0);
         truncate_inode_pages(&inode->i_data, 0);
 
-        if (atomic_read(&gl->gl_revokes) == 0) {
+        if (!test_bit(GLF_REVOKES, &gl->gl_flags)) {
                 clear_bit(GLF_LFLUSH, &gl->gl_flags);
                 clear_bit(GLF_DIRTY, &gl->gl_flags);
         }