[PATCH 3/4] bcache: notify allocator to prepare for GC

[tang.junhui@zte.com.cn]

From: Tang Junhui <tang.junhui@zte.com.cn>

Since no new bucket can be allocated during GC, and front side I/Os would
run out of all the buckets, so notify allocator to pack the free_inc queue
full of buckets before GC, then we could have enough buckets for front side
I/Os during GC period.

Signed-off-by: Tang Junhui <tang.junhui@zte.com.cn>
---
 drivers/md/bcache/alloc.c  | 11 +++++++-
 drivers/md/bcache/bcache.h |  2 ++
 drivers/md/bcache/btree.c  | 69 ++++++++++++++++++++++++++++++++++++++++++++--
 drivers/md/bcache/btree.h  |  4 +++
 4 files changed, 83 insertions(+), 3 deletions(-)

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index a0cc1bc..85020cc 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -323,7 +323,8 @@ static int bch_allocator_thread(void *arg)
 		 * possibly issue discards to them, then we add the bucket to
 		 * the free list:
 		 */
-		while (!fifo_empty(&ca->free_inc)) {
+		while (!fifo_empty(&ca->free_inc) &&
+		       ca->prepare_gc != GC_PREPARING) {
 			long bucket;
 
 			fifo_pop(&ca->free_inc, bucket);
@@ -353,6 +354,14 @@ static int bch_allocator_thread(void *arg)
 		invalidate_buckets(ca);
 
 		/*
+		 * Let GC continue
+		 */
+		if (ca->prepare_gc == GC_PREPARING) {
+			ca->prepare_gc = GC_PREPARED;
+			wake_up_gc(ca->set);
+		}
+
+		/*
 		 * Now, we write their new gens to disk so we can start writing
 		 * new stuff to them:
 		 */
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index ab4c9ca..61a6ff2 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -428,6 +428,8 @@ struct cache {
 	 * cpu
 	 */
 	unsigned		invalidate_needs_gc;
+	/* used to notify allocator to prepare GC*/
+	unsigned int		prepare_gc;
 
 	bool			discard; /* Get rid of? */
 
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 10f967e..aba0700 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1805,6 +1805,46 @@ static void bch_btree_gc(struct cache_set *c)
 	bch_moving_gc(c);
 }
 
+static bool cache_gc_prepare_none(struct cache_set *c)
+{
+	struct cache *ca;
+	unsigned int i;
+
+	for_each_cache(ca, c, i)
+		if (ca->prepare_gc != GC_PREPARE_NONE)
+			return false;
+	return true;
+}
+
+static bool cache_gc_prepare_ok(struct cache_set *c)
+{
+	struct cache *ca;
+	unsigned int i;
+
+	for_each_cache(ca, c, i)
+		if (ca->prepare_gc != GC_PREPARED)
+			return false;
+	return true;
+}
+
+static void set_cache_gc_prepare_none(struct cache_set *c)
+{
+	struct cache *ca;
+	unsigned int i;
+
+	for_each_cache(ca, c, i)
+		ca->prepare_gc = GC_PREPARE_NONE;
+}
+
+static void set_cache_gc_preparing(struct cache_set *c)
+{
+	struct cache *ca;
+	unsigned int i;
+
+	for_each_cache(ca, c, i)
+		ca->prepare_gc = GC_PREPARING;
+}
+
 static bool gc_should_run(struct cache_set *c)
 {
 	struct cache *ca;
@@ -1814,8 +1854,33 @@ static bool gc_should_run(struct cache_set *c)
 		if (ca->invalidate_needs_gc)
 			return true;
 
-	if (atomic_read(&c->sectors_to_gc) < 0)
-		return true;
+	if (atomic_read(&c->sectors_to_gc) < 0) {
+		mutex_lock(&c->bucket_lock);
+		if (cache_gc_prepare_none(c)) {
+			/*
+			 * notify allocator thread to prepare for GC
+			 */
+			set_cache_gc_preparing(c);
+			mutex_unlock(&c->bucket_lock);
+			pr_info("gc preparing");
+			return false;
+		} else if (cache_gc_prepare_ok(c)) {
+			/*
+			 * alloc thread finished preparing,
+			 * and continue to GC
+			 */
+			set_cache_gc_prepare_none(c);
+			mutex_unlock(&c->bucket_lock);
+			pr_info("gc prepared ok");
+			return true;
+		} else {
+			/*
+			 * waitting allocator finishing prepareing
+			 */
+			mutex_unlock(&c->bucket_lock);
+			return false;
+		}
+	}
 
 	return false;
 }
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index d211e2c..e60bd7a 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -102,6 +102,10 @@
 #include "bset.h"
 #include "debug.h"
 
+#define GC_PREPARE_NONE		0
+#define GC_PREPARING		1
+#define GC_PREPARED		2
+
 struct btree_write {
 	atomic_t		*journal;
 
-- 
1.8.3.1