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[Cluster-devel] GFS2: Use RCU for glock hash table



Hi,

This patch is in the early stages of development, but I'm posting it now
to give a heads up on what I'm planning. You can seen from this diffstat
that it is another reduction in the code, of about 100 lines or so and most
of that is from glock.c

 fs/gfs2/glock.c         |  357 ++++++++++++++++--------------------------------
 fs/gfs2/glock.h         |   39 ++---
 fs/gfs2/glops.c         |   23 +--
 fs/gfs2/incore.h        |    2 
 fs/gfs2/lock_dlm.c      |   14 -
 fs/gfs2/lops.c          |    3 
 fs/gfs2/main.c          |    3 
 fs/gfs2/ops_fstype.c    |    7 
 include/linux/rculist.h |   13 +
 9 files changed, 178 insertions(+), 283 deletions(-)

The plan, which I've had for a long time, is to convert the glock hash table to
use RCU rather than the current rwlocks. This should improve scalability on
multi-core machines and also results in a simplification of the code at the same
time.

I've given this patch some initial testing and it seems to stand up well, however
there are a number of things I'm comtemplating doing before this goes into the tree:

1. Replacement of sd_glock_disposal counter with a percpu counter
2. Using an RCU version of the hlist_bl proposed for the inode cache in order to
   split the hash_lock introduced in the patch. Originally I'd considered just
   using the lru_lock for both purposes, but I'm not sure that will be good enough.
   Further testing will be required to find out.
3. Moving the decrement of the sd_glock_disposal counter so that it happens before
   the call_rcu() - its probably not a big deal, but it would make more sense
4. Making the atomic_dec_and_lock() part of gfs2_glock_put into an inline that calls
   the remainder of the function if required

The patch changes when glocks are added to the lru list. This was done in order to
streamline gfs2_glock_put() however I've yet to verify that this hasn't created any
unwanted side-effects. One consequence of this is that glocks related to journaled
metadata will not be put on the lru list until after their exit from the journal.
This acts as an additional check that we are not trying to demote glocks too early.


diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 8777885..264030f 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -26,6 +26,8 @@
 #include <linux/freezer.h>
 #include <linux/workqueue.h>
 #include <linux/jiffies.h>
+#include <linux/rcupdate.h>
+#include <linux/rculist.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -54,7 +56,6 @@ struct gfs2_glock_iter {
 
 typedef void (*glock_examiner) (struct gfs2_glock * gl);
 
-static int gfs2_dump_lockstate(struct gfs2_sbd *sdp);
 static int __dump_glock(struct seq_file *seq, const struct gfs2_glock *gl);
 #define GLOCK_BUG_ON(gl,x) do { if (unlikely(x)) { __dump_glock(NULL, gl); BUG(); } } while(0)
 static void do_xmote(struct gfs2_glock *gl, struct gfs2_holder *gh, unsigned int target);
@@ -65,6 +66,7 @@ struct workqueue_struct *gfs2_delete_workqueue;
 static LIST_HEAD(lru_list);
 static atomic_t lru_count = ATOMIC_INIT(0);
 static DEFINE_SPINLOCK(lru_lock);
+static DEFINE_SPINLOCK(hash_lock);
 
 #define GFS2_GL_HASH_SHIFT      15
 #define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
@@ -73,54 +75,6 @@ static DEFINE_SPINLOCK(lru_lock);
 static struct gfs2_gl_hash_bucket gl_hash_table[GFS2_GL_HASH_SIZE];
 static struct dentry *gfs2_root;
 
-/*
- * Despite what you might think, the numbers below are not arbitrary :-)
- * They are taken from the ipv4 routing hash code, which is well tested
- * and thus should be nearly optimal. Later on we might tweek the numbers
- * but for now this should be fine.
- *
- * The reason for putting the locks in a separate array from the list heads
- * is that we can have fewer locks than list heads and save memory. We use
- * the same hash function for both, but with a different hash mask.
- */
-#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) || \
-	defined(CONFIG_PROVE_LOCKING)
-
-#ifdef CONFIG_LOCKDEP
-# define GL_HASH_LOCK_SZ        256
-#else
-# if NR_CPUS >= 32
-#  define GL_HASH_LOCK_SZ       4096
-# elif NR_CPUS >= 16
-#  define GL_HASH_LOCK_SZ       2048
-# elif NR_CPUS >= 8
-#  define GL_HASH_LOCK_SZ       1024
-# elif NR_CPUS >= 4
-#  define GL_HASH_LOCK_SZ       512
-# else
-#  define GL_HASH_LOCK_SZ       256
-# endif
-#endif
-
-/* We never want more locks than chains */
-#if GFS2_GL_HASH_SIZE < GL_HASH_LOCK_SZ
-# undef GL_HASH_LOCK_SZ
-# define GL_HASH_LOCK_SZ GFS2_GL_HASH_SIZE
-#endif
-
-static rwlock_t gl_hash_locks[GL_HASH_LOCK_SZ];
-
-static inline rwlock_t *gl_lock_addr(unsigned int x)
-{
-	return &gl_hash_locks[x & (GL_HASH_LOCK_SZ-1)];
-}
-#else /* not SMP, so no spinlocks required */
-static inline rwlock_t *gl_lock_addr(unsigned int x)
-{
-	return NULL;
-}
-#endif
-
 /**
  * gl_hash() - Turn glock number into hash bucket number
  * @lock: The glock number
@@ -141,25 +95,18 @@ static unsigned int gl_hash(const struct gfs2_sbd *sdp,
 	return h;
 }
 
-/**
- * glock_free() - Perform a few checks and then release struct gfs2_glock
- * @gl: The glock to release
- *
- * Also calls lock module to release its internal structure for this glock.
- *
- */
-
-static void glock_free(struct gfs2_glock *gl)
+void gfs2_glock_free(struct rcu_head *rcu)
 {
+	struct gfs2_glock *gl = container_of(rcu, struct gfs2_glock, gl_rcu);
 	struct gfs2_sbd *sdp = gl->gl_sbd;
-	struct address_space *mapping = gfs2_glock2aspace(gl);
-	struct kmem_cache *cachep = gfs2_glock_cachep;
 
-	GLOCK_BUG_ON(gl, mapping && mapping->nrpages);
-	trace_gfs2_glock_put(gl);
-	if (mapping)
-		cachep = gfs2_glock_aspace_cachep;
-	sdp->sd_lockstruct.ls_ops->lm_put_lock(cachep, gl);
+	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);
 }
 
 /**
@@ -185,34 +132,49 @@ static int demote_ok(const struct gfs2_glock *gl)
 {
 	const struct gfs2_glock_operations *glops = gl->gl_ops;
 
+	assert_spin_locked(&gl->gl_spin);
+
 	if (gl->gl_state == LM_ST_UNLOCKED)
 		return 0;
-	if (!list_empty(&gl->gl_holders))
+	if (test_bit(GLF_LFLUSH, &gl->gl_flags))
+		return 0;
+	if ((gl->gl_name.ln_type != LM_TYPE_INODE) &&
+	    !list_empty(&gl->gl_holders))
 		return 0;
 	if (glops->go_demote_ok)
 		return glops->go_demote_ok(gl);
 	return 1;
 }
 
+
 /**
- * gfs2_glock_schedule_for_reclaim - Add a glock to the reclaim list
+ * __gfs2_glock_schedule_for_reclaim - Add a glock to the reclaim list
  * @gl: the glock
  *
+ * If the glock is demotable, then we add it (or move it) to the end
+ * of the glock LRU list.
  */
 
-static void gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl)
+static void __gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl)
 {
-	int may_reclaim;
-	may_reclaim = (demote_ok(gl) &&
-		       (atomic_read(&gl->gl_ref) == 1 ||
-			(gl->gl_name.ln_type == LM_TYPE_INODE &&
-			 atomic_read(&gl->gl_ref) <= 2)));
-	spin_lock(&lru_lock);
-	if (list_empty(&gl->gl_lru) && may_reclaim) {
+	if (demote_ok(gl)) {
+		spin_lock(&lru_lock);
+
+		if (!list_empty(&gl->gl_lru))
+			list_del_init(&gl->gl_lru);
+		else
+			atomic_inc(&lru_count);
+
 		list_add_tail(&gl->gl_lru, &lru_list);
-		atomic_inc(&lru_count);
+		spin_unlock(&lru_lock);
 	}
-	spin_unlock(&lru_lock);
+}
+
+void gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl)
+{
+	spin_lock(&gl->gl_spin);
+	__gfs2_glock_schedule_for_reclaim(gl);
+	spin_unlock(&gl->gl_spin);
 }
 
 /**
@@ -227,7 +189,6 @@ void gfs2_glock_put_nolock(struct gfs2_glock *gl)
 {
 	if (atomic_dec_and_test(&gl->gl_ref))
 		GLOCK_BUG_ON(gl, 1);
-	gfs2_glock_schedule_for_reclaim(gl);
 }
 
 /**
@@ -236,30 +197,25 @@ void gfs2_glock_put_nolock(struct gfs2_glock *gl)
  *
  */
 
-int gfs2_glock_put(struct gfs2_glock *gl)
+void gfs2_glock_put(struct gfs2_glock *gl)
 {
-	int rv = 0;
+	struct gfs2_sbd *sdp = gl->gl_sbd;
+	struct address_space *mapping = gfs2_glock2aspace(gl);
 
-	write_lock(gl_lock_addr(gl->gl_hash));
-	if (atomic_dec_and_lock(&gl->gl_ref, &lru_lock)) {
-		hlist_del(&gl->gl_list);
+	if (atomic_dec_and_lock(&gl->gl_ref, &hash_lock)) {
+		hlist_del_rcu(&gl->gl_list);
+		spin_unlock(&hash_lock);
+		spin_lock(&lru_lock);
 		if (!list_empty(&gl->gl_lru)) {
 			list_del_init(&gl->gl_lru);
 			atomic_dec(&lru_count);
 		}
 		spin_unlock(&lru_lock);
-		write_unlock(gl_lock_addr(gl->gl_hash));
 		GLOCK_BUG_ON(gl, !list_empty(&gl->gl_holders));
-		glock_free(gl);
-		rv = 1;
-		goto out;
+		GLOCK_BUG_ON(gl, mapping && mapping->nrpages);
+		trace_gfs2_glock_put(gl);
+		sdp->sd_lockstruct.ls_ops->lm_put_lock(gl);
 	}
-	spin_lock(&gl->gl_spin);
-	gfs2_glock_schedule_for_reclaim(gl);
-	spin_unlock(&gl->gl_spin);
-	write_unlock(gl_lock_addr(gl->gl_hash));
-out:
-	return rv;
 }
 
 /**
@@ -277,15 +233,13 @@ static struct gfs2_glock *search_bucket(unsigned int hash,
 	struct gfs2_glock *gl;
 	struct hlist_node *h;
 
-	hlist_for_each_entry(gl, h, &gl_hash_table[hash].hb_list, gl_list) {
+	hlist_for_each_entry_rcu(gl, h, &gl_hash_table[hash].hb_list, gl_list) {
 		if (!lm_name_equal(&gl->gl_name, name))
 			continue;
 		if (gl->gl_sbd != sdp)
 			continue;
-
-		atomic_inc(&gl->gl_ref);
-
-		return gl;
+		if (atomic_inc_not_zero(&gl->gl_ref))
+			return gl;
 	}
 
 	return NULL;
@@ -756,10 +710,11 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 	struct gfs2_glock *gl, *tmp;
 	unsigned int hash = gl_hash(sdp, &name);
 	struct address_space *mapping;
+	struct kmem_cache *cachep;
 
-	read_lock(gl_lock_addr(hash));
+	rcu_read_lock();
 	gl = search_bucket(hash, sdp, &name);
-	read_unlock(gl_lock_addr(hash));
+	rcu_read_unlock();
 
 	*glp = gl;
 	if (gl)
@@ -768,9 +723,10 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 		return -ENOENT;
 
 	if (glops->go_flags & GLOF_ASPACE)
-		gl = kmem_cache_alloc(gfs2_glock_aspace_cachep, GFP_KERNEL);
+		cachep = gfs2_glock_aspace_cachep;
 	else
-		gl = kmem_cache_alloc(gfs2_glock_cachep, GFP_KERNEL);
+		cachep = gfs2_glock_cachep;
+	gl = kmem_cache_alloc(cachep, GFP_KERNEL);
 	if (!gl)
 		return -ENOMEM;
 
@@ -803,15 +759,15 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
 		mapping->writeback_index = 0;
 	}
 
-	write_lock(gl_lock_addr(hash));
+	spin_lock(&hash_lock);
 	tmp = search_bucket(hash, sdp, &name);
 	if (tmp) {
-		write_unlock(gl_lock_addr(hash));
-		glock_free(gl);
+		spin_unlock(&hash_lock);
+		kmem_cache_free(cachep, gl);
 		gl = tmp;
 	} else {
-		hlist_add_head(&gl->gl_list, &gl_hash_table[hash].hb_list);
-		write_unlock(gl_lock_addr(hash));
+		hlist_add_head_rcu(&gl->gl_list, &gl_hash_table[hash].hb_list);
+		spin_unlock(&hash_lock);
 	}
 
 	*glp = gl;
@@ -1121,6 +1077,7 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
 		    !test_bit(GLF_DEMOTE, &gl->gl_flags))
 			fast_path = 1;
 	}
+	__gfs2_glock_schedule_for_reclaim(gl);
 	trace_gfs2_glock_queue(gh, 0);
 	spin_unlock(&gl->gl_spin);
 	if (likely(fast_path))
@@ -1444,42 +1401,30 @@ static struct shrinker glock_shrinker = {
  * @sdp: the filesystem
  * @bucket: the bucket
  *
- * Returns: 1 if the bucket has entries
  */
 
-static int examine_bucket(glock_examiner examiner, struct gfs2_sbd *sdp,
+static void examine_bucket(glock_examiner examiner, const struct gfs2_sbd *sdp,
 			  unsigned int hash)
 {
-	struct gfs2_glock *gl, *prev = NULL;
-	int has_entries = 0;
+	struct gfs2_glock *gl;
 	struct hlist_head *head = &gl_hash_table[hash].hb_list;
+	struct hlist_node *pos;
 
-	read_lock(gl_lock_addr(hash));
-	/* Can't use hlist_for_each_entry - don't want prefetch here */
-	if (hlist_empty(head))
-		goto out;
-	gl = list_entry(head->first, struct gfs2_glock, gl_list);
-	while(1) {
-		if (!sdp || gl->gl_sbd == sdp) {
-			gfs2_glock_hold(gl);
-			read_unlock(gl_lock_addr(hash));
-			if (prev)
-				gfs2_glock_put(prev);
-			prev = gl;
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(gl, pos, head, gl_list) {
+		if ((gl->gl_sbd == sdp) && atomic_read(&gl->gl_ref))
 			examiner(gl);
-			has_entries = 1;
-			read_lock(gl_lock_addr(hash));
-		}
-		if (gl->gl_list.next == NULL)
-			break;
-		gl = list_entry(gl->gl_list.next, struct gfs2_glock, gl_list);
 	}
-out:
-	read_unlock(gl_lock_addr(hash));
-	if (prev)
-		gfs2_glock_put(prev);
+	rcu_read_unlock();
 	cond_resched();
-	return has_entries;
+}
+
+static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
+{
+	unsigned x;
+
+	for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
+		examine_bucket(examiner, sdp, x);
 }
 

@@ -1533,10 +1478,21 @@ static void clear_glock(struct gfs2_glock *gl)
 
 void gfs2_glock_thaw(struct gfs2_sbd *sdp)
 {
-	unsigned x;
+	glock_hash_walk(thaw_glock, sdp);
+}
 
-	for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
-		examine_bucket(thaw_glock, sdp, x);
+static int dump_glock(struct seq_file *seq, struct gfs2_glock *gl)
+{
+	int ret;
+	spin_lock(&gl->gl_spin);
+	ret = __dump_glock(seq, gl);
+	spin_unlock(&gl->gl_spin);
+	return ret;
+}
+
+static void dump_glock_func(struct gfs2_glock *gl)
+{
+	dump_glock(NULL, gl);
 }
 
 /**
@@ -1549,13 +1505,10 @@ void gfs2_glock_thaw(struct gfs2_sbd *sdp)
 
 void gfs2_gl_hash_clear(struct gfs2_sbd *sdp)
 {
-	unsigned int x;
-
-	for (x = 0; x < GFS2_GL_HASH_SIZE; x++)
-		examine_bucket(clear_glock, sdp, x);
+	glock_hash_walk(clear_glock, sdp);
 	flush_workqueue(glock_workqueue);
 	wait_event(sdp->sd_glock_wait, atomic_read(&sdp->sd_glock_disposal) == 0);
-	gfs2_dump_lockstate(sdp);
+	glock_hash_walk(dump_glock_func, sdp);
 }
 
 void gfs2_glock_finish_truncate(struct gfs2_inode *ip)
@@ -1722,53 +1675,7 @@ out:
 	return error;
 }
 
-static int dump_glock(struct seq_file *seq, struct gfs2_glock *gl)
-{
-	int ret;
-	spin_lock(&gl->gl_spin);
-	ret = __dump_glock(seq, gl);
-	spin_unlock(&gl->gl_spin);
-	return ret;
-}
-
-/**
- * gfs2_dump_lockstate - print out the current lockstate
- * @sdp: the filesystem
- * @ub: the buffer to copy the information into
- *
- * If @ub is NULL, dump the lockstate to the console.
- *
- */
 
-static int gfs2_dump_lockstate(struct gfs2_sbd *sdp)
-{
-	struct gfs2_glock *gl;
-	struct hlist_node *h;
-	unsigned int x;
-	int error = 0;
-
-	for (x = 0; x < GFS2_GL_HASH_SIZE; x++) {
-
-		read_lock(gl_lock_addr(x));
-
-		hlist_for_each_entry(gl, h, &gl_hash_table[x].hb_list, gl_list) {
-			if (gl->gl_sbd != sdp)
-				continue;
-
-			error = dump_glock(NULL, gl);
-			if (error)
-				break;
-		}
-
-		read_unlock(gl_lock_addr(x));
-
-		if (error)
-			break;
-	}
-
-
-	return error;
-}
 

 int __init gfs2_glock_init(void)
@@ -1806,62 +1713,49 @@ void gfs2_glock_exit(void)
 	destroy_workqueue(gfs2_delete_workqueue);
 }
 
+static inline struct gfs2_glock *glock_hash_chain(unsigned hash)
+{
+	return hlist_entry_rcu(gl_hash_table[hash].hb_list.first,
+			       struct gfs2_glock, gl_list);
+}
+
 static int gfs2_glock_iter_next(struct gfs2_glock_iter *gi)
 {
 	struct gfs2_glock *gl;
 
-restart:
-	read_lock(gl_lock_addr(gi->hash));
-	gl = gi->gl;
-	if (gl) {
-		gi->gl = hlist_entry(gl->gl_list.next,
-				     struct gfs2_glock, gl_list);
-	} else {
-		gi->gl = hlist_entry(gl_hash_table[gi->hash].hb_list.first,
-				     struct gfs2_glock, gl_list);
-	}
-	if (gi->gl)
-		gfs2_glock_hold(gi->gl);
-	read_unlock(gl_lock_addr(gi->hash));
-	if (gl)
-		gfs2_glock_put(gl);
-	while (gi->gl == NULL) {
-		gi->hash++;
-		if (gi->hash >= GFS2_GL_HASH_SIZE)
-			return 1;
-		read_lock(gl_lock_addr(gi->hash));
-		gi->gl = hlist_entry(gl_hash_table[gi->hash].hb_list.first,
-				     struct gfs2_glock, gl_list);
-		if (gi->gl)
-			gfs2_glock_hold(gi->gl);
-		read_unlock(gl_lock_addr(gi->hash));
-	}
-
-	if (gi->sdp != gi->gl->gl_sbd)
-		goto restart;
+	do {
+		gl = gi->gl;
+		if (gl) {
+			gi->gl = hlist_entry_rcu(gl->gl_list.next,
+						 struct gfs2_glock, gl_list);
+		} else {
+			gi->gl = glock_hash_chain(gi->hash);
+		}
+		while (gi->gl == NULL) {
+			gi->hash++;
+			if (gi->hash >= GFS2_GL_HASH_SIZE) {
+				rcu_read_unlock();
+				return 1;
+			}
+			gi->gl = glock_hash_chain(gi->hash);
+		}
+	/* Skip entries for other sb and dead entries */
+	} while (gi->sdp != gi->gl->gl_sbd || atomic_read(&gi->gl->gl_ref) == 0);
 
 	return 0;
 }
 
-static void gfs2_glock_iter_free(struct gfs2_glock_iter *gi)
-{
-	if (gi->gl)
-		gfs2_glock_put(gi->gl);
-	gi->gl = NULL;
-}
-
 static void *gfs2_glock_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	struct gfs2_glock_iter *gi = seq->private;
 	loff_t n = *pos;
 
 	gi->hash = 0;
+	rcu_read_lock();
 
 	do {
-		if (gfs2_glock_iter_next(gi)) {
-			gfs2_glock_iter_free(gi);
+		if (gfs2_glock_iter_next(gi))
 			return NULL;
-		}
 	} while (n--);
 
 	return gi->gl;
@@ -1874,10 +1768,8 @@ static void *gfs2_glock_seq_next(struct seq_file *seq, void *iter_ptr,
 
 	(*pos)++;
 
-	if (gfs2_glock_iter_next(gi)) {
-		gfs2_glock_iter_free(gi);
+	if (gfs2_glock_iter_next(gi))
 		return NULL;
-	}
 
 	return gi->gl;
 }
@@ -1885,7 +1777,10 @@ static void *gfs2_glock_seq_next(struct seq_file *seq, void *iter_ptr,
 static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr)
 {
 	struct gfs2_glock_iter *gi = seq->private;
-	gfs2_glock_iter_free(gi);
+
+	if (gi->gl)
+		rcu_read_unlock();
+	gi->gl = NULL;
 }
 
 static int gfs2_glock_seq_show(struct seq_file *seq, void *iter_ptr)
diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index 2bda191..4453912 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -123,7 +123,7 @@ struct lm_lockops {
 	int (*lm_mount) (struct gfs2_sbd *sdp, const char *fsname);
  	void (*lm_unmount) (struct gfs2_sbd *sdp);
 	void (*lm_withdraw) (struct gfs2_sbd *sdp);
-	void (*lm_put_lock) (struct kmem_cache *cachep, struct gfs2_glock *gl);
+	void (*lm_put_lock) (struct gfs2_glock *gl);
 	unsigned int (*lm_lock) (struct gfs2_glock *gl,
 				 unsigned int req_state, unsigned int flags);
 	void (*lm_cancel) (struct gfs2_glock *gl);
@@ -192,7 +192,7 @@ int gfs2_glock_get(struct gfs2_sbd *sdp,
 		   int create, struct gfs2_glock **glp);
 void gfs2_glock_hold(struct gfs2_glock *gl);
 void gfs2_glock_put_nolock(struct gfs2_glock *gl);
-int gfs2_glock_put(struct gfs2_glock *gl);
+void gfs2_glock_put(struct gfs2_glock *gl);
 void gfs2_holder_init(struct gfs2_glock *gl, unsigned int state, unsigned flags,
 		      struct gfs2_holder *gh);
 void gfs2_holder_reinit(unsigned int state, unsigned flags,
@@ -239,25 +239,22 @@ static inline int gfs2_glock_nq_init(struct gfs2_glock *gl,
 	return error;
 }
 
-/*  Lock Value Block functions  */
-
-int gfs2_lvb_hold(struct gfs2_glock *gl);
-void gfs2_lvb_unhold(struct gfs2_glock *gl);
-
-void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state);
-void gfs2_glock_complete(struct gfs2_glock *gl, int ret);
-void gfs2_reclaim_glock(struct gfs2_sbd *sdp);
-void gfs2_gl_hash_clear(struct gfs2_sbd *sdp);
-void gfs2_glock_finish_truncate(struct gfs2_inode *ip);
-void gfs2_glock_thaw(struct gfs2_sbd *sdp);
-
-int __init gfs2_glock_init(void);
-void gfs2_glock_exit(void);
-
-int gfs2_create_debugfs_file(struct gfs2_sbd *sdp);
-void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp);
-int gfs2_register_debugfs(void);
-void gfs2_unregister_debugfs(void);
+extern void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state);
+extern void gfs2_glock_complete(struct gfs2_glock *gl, int ret);
+extern void gfs2_reclaim_glock(struct gfs2_sbd *sdp);
+extern void gfs2_gl_hash_clear(struct gfs2_sbd *sdp);
+extern void gfs2_glock_finish_truncate(struct gfs2_inode *ip);
+extern void gfs2_glock_thaw(struct gfs2_sbd *sdp);
+extern void gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl);
+extern void gfs2_glock_free(struct rcu_head *rcu);
+
+extern int __init gfs2_glock_init(void);
+extern void gfs2_glock_exit(void);
+
+extern int gfs2_create_debugfs_file(struct gfs2_sbd *sdp);
+extern void gfs2_delete_debugfs_file(struct gfs2_sbd *sdp);
+extern int gfs2_register_debugfs(void);
+extern void gfs2_unregister_debugfs(void);
 
 extern const struct lm_lockops gfs2_dlm_ops;
 
diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 0d149dc..31838ef 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -206,8 +206,17 @@ static void inode_go_inval(struct gfs2_glock *gl, int flags)
 static int inode_go_demote_ok(const struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
+	struct gfs2_holder *gh;
+
 	if (sdp->sd_jindex == gl->gl_object || sdp->sd_rindex == gl->gl_object)
 		return 0;
+
+	if (!list_empty(&gl->gl_holders)) {
+		gh = list_entry(gl->gl_holders.next, struct gfs2_holder, gh_list);
+		if (gh->gh_list.next != &gl->gl_holders)
+			return 0;
+	}
+
 	return 1;
 }
 
@@ -272,19 +281,6 @@ static int inode_go_dump(struct seq_file *seq, const struct gfs2_glock *gl)
 }
 
 /**
- * rgrp_go_demote_ok - Check to see if it's ok to unlock a RG's glock
- * @gl: the glock
- *
- * Returns: 1 if it's ok
- */
-
-static int rgrp_go_demote_ok(const struct gfs2_glock *gl)
-{
-	const struct address_space *mapping = (const struct address_space *)(gl + 1);
-	return !mapping->nrpages;
-}
-
-/**
  * rgrp_go_lock - operation done after an rgrp lock is locked by
  *    a first holder on this node.
  * @gl: the glock
@@ -411,7 +407,6 @@ const struct gfs2_glock_operations gfs2_inode_glops = {
 const struct gfs2_glock_operations gfs2_rgrp_glops = {
 	.go_xmote_th = rgrp_go_sync,
 	.go_inval = rgrp_go_inval,
-	.go_demote_ok = rgrp_go_demote_ok,
 	.go_lock = rgrp_go_lock,
 	.go_unlock = rgrp_go_unlock,
 	.go_dump = gfs2_rgrp_dump,
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 764fbb4..602c2aa 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -14,6 +14,7 @@
 #include <linux/workqueue.h>
 #include <linux/dlm.h>
 #include <linux/buffer_head.h>
+#include <linux/rcupdate.h>
 
 #define DIO_WAIT	0x00000010
 #define DIO_METADATA	0x00000020
@@ -231,6 +232,7 @@ struct gfs2_glock {
 	atomic_t gl_ail_count;
 	struct delayed_work gl_work;
 	struct work_struct gl_delete;
+	struct rcu_head gl_rcu;
 };
 
 #define GFS2_MIN_LVB_SIZE 32	/* Min size of LVB that gfs2 supports */
diff --git a/fs/gfs2/lock_dlm.c b/fs/gfs2/lock_dlm.c
index 1c09425..ba7ab71 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;
@@ -171,16 +165,14 @@ static unsigned int gdlm_lock(struct gfs2_glock *gl,
 	return LM_OUT_ASYNC;
 }
 
-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;
 	}
 
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index bf33f82..11a73ef 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -91,7 +91,8 @@ static void gfs2_unpin(struct gfs2_sbd *sdp, struct buffer_head *bh,
 	}
 	bd->bd_ail = ai;
 	list_add(&bd->bd_ail_st_list, &ai->ai_ail1_list);
-	clear_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags);
+	if (test_and_clear_bit(GLF_LFLUSH, &bd->bd_gl->gl_flags))
+		gfs2_glock_schedule_for_reclaim(bd->bd_gl);
 	trace_gfs2_pin(bd, 0);
 	gfs2_log_unlock(sdp);
 	unlock_buffer(bh);
diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c
index d7eb1e2..c99fe49 100644
--- a/fs/gfs2/main.c
+++ b/fs/gfs2/main.c
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/gfs2_ondisk.h>
+#include <linux/rcupdate.h>
 #include <asm/atomic.h>
 
 #include "gfs2.h"
@@ -198,6 +199,8 @@ static void __exit exit_gfs2_fs(void)
 	unregister_filesystem(&gfs2meta_fs_type);
 	destroy_workqueue(gfs_recovery_wq);
 
+	rcu_barrier();
+
 	kmem_cache_destroy(gfs2_quotad_cachep);
 	kmem_cache_destroy(gfs2_rgrpd_cachep);
 	kmem_cache_destroy(gfs2_bufdata_cachep);
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index aeafc23..cc82532 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -929,12 +929,9 @@ static const match_table_t nolock_tokens = {
 	{ Opt_err, NULL },
 };
 
-static void nolock_put_lock(struct kmem_cache *cachep, struct gfs2_glock *gl)
+static void nolock_put_lock(struct gfs2_glock *gl)
 {
-	struct gfs2_sbd *sdp = gl->gl_sbd;
-	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);
 }
 
 static const struct lm_lockops nolock_ops = {
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4ec3b38..6b6079e 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -276,6 +276,19 @@ static inline void list_splice_init_rcu(struct list_head *list,
 	     pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**
+ * hlist_entry_rcu - get the struct for this entry
+ * @ptr:        the &struct list_head pointer.
+ * @type:       the type of the struct this is embedded in.
+ * @member:     the name of the list_struct within the struct.
+ *
+ * This primitive may safely run concurrently with the _rcu list-mutation
+ * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
+ */
+
+#define hlist_entry_rcu(ptr, type, member) \
+	container_of(rcu_dereference_raw(ptr),type,member)
+
+/**
  * hlist_del_rcu - deletes entry from hash list without re-initialization
  * @n: the element to delete from the hash list.
  *




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