4 files changed, 52 insertions, 0 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 96d2213f279e..fdf75352e16a 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -627,6 +627,20 @@ struct cache_set {
 	struct bkey		gc_done;
 
 	/*
+	 * For automatical garbage collection after writeback completed, this
+	 * varialbe is used as bit fields,
+	 * - 0000 0001b (BCH_ENABLE_AUTO_GC): enable gc after writeback
+	 * - 0000 0010b (BCH_DO_AUTO_GC):     do gc after writeback
+	 * This is an optimization for following write request after writeback
+	 * finished, but read hit rate dropped due to clean data on cache is
+	 * discarded. Unless user explicitly sets it via sysfs, it won't be
+	 * enabled.
+	 */
+#define BCH_ENABLE_AUTO_GC	1
+#define BCH_DO_AUTO_GC		2
+	uint8_t			gc_after_writeback;
+
+	/*
 	 * The allocation code needs gc_mark in struct bucket to be correct, but
 	 * it's not while a gc is in progress. Protected by bucket_lock.
 	 */
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index c09748497cdc..621186b4240f 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -128,6 +128,7 @@ rw_attribute(expensive_debug_checks);
 rw_attribute(cache_replacement_policy);
 rw_attribute(btree_shrinker_disabled);
 rw_attribute(copy_gc_enabled);
+rw_attribute(gc_after_writeback);
 rw_attribute(size);
 
 static ssize_t bch_snprint_string_list(char *buf,
@@ -693,6 +694,7 @@ SHOW(__bch_cache_set)
 	sysfs_printf(gc_always_rewrite,		"%i", c->gc_always_rewrite);
 	sysfs_printf(btree_shrinker_disabled,	"%i", c->shrinker_disabled);
 	sysfs_printf(copy_gc_enabled,		"%i", c->copy_gc_enabled);
+	sysfs_printf(gc_after_writeback,	"%i", c->gc_after_writeback);
 	sysfs_printf(io_disable,		"%i",
 		     test_bit(CACHE_SET_IO_DISABLE, &c->flags));
 
@@ -793,6 +795,12 @@ STORE(__bch_cache_set)
 	sysfs_strtoul(gc_always_rewrite,	c->gc_always_rewrite);
 	sysfs_strtoul(btree_shrinker_disabled,	c->shrinker_disabled);
 	sysfs_strtoul(copy_gc_enabled,		c->copy_gc_enabled);
+	/*
+	 * write gc_after_writeback here may overwrite an already set
+	 * BCH_DO_AUTO_GC, it doesn't matter because this flag will be
+	 * set in next chance.
+	 */
+	sysfs_strtoul_clamp(gc_after_writeback, c->gc_after_writeback, 0, 1);
 
 	return size;
 }
@@ -873,6 +881,7 @@ static struct attribute *bch_cache_set_internal_files[] = {
 	&sysfs_gc_always_rewrite,
 	&sysfs_btree_shrinker_disabled,
 	&sysfs_copy_gc_enabled,
+	&sysfs_gc_after_writeback,
 	&sysfs_io_disable,
 	NULL
 };
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 1696b212ec4e..73f0efac2b9f 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -17,6 +17,15 @@
 #include <linux/sched/clock.h>
 #include <trace/events/bcache.h>
 
+static void update_gc_after_writeback(struct cache_set *c)
+{
+	if (c->gc_after_writeback != (BCH_ENABLE_AUTO_GC) ||
+	    c->gc_stats.in_use < BCH_AUTO_GC_DIRTY_THRESHOLD)
+		return;
+
+	c->gc_after_writeback |= BCH_DO_AUTO_GC;
+}
+
 /* Rate limiting */
 static uint64_t __calc_target_rate(struct cached_dev *dc)
 {
@@ -191,6 +200,7 @@ static void update_writeback_rate(struct work_struct *work)
 		if (!set_at_max_writeback_rate(c, dc)) {
 			down_read(&dc->writeback_lock);
 			__update_writeback_rate(dc);
+			update_gc_after_writeback(c);
 			up_read(&dc->writeback_lock);
 		}
 	}
@@ -689,6 +699,23 @@ static int bch_writeback_thread(void *arg)
 				up_write(&dc->writeback_lock);
 				break;
 			}
+
+			/*
+			 * When dirty data rate is high (e.g. 50%+), there might
+			 * be heavy buckets fragmentation after writeback
+			 * finished, which hurts following write performance.
+			 * If users really care about write performance they
+			 * may set BCH_ENABLE_AUTO_GC via sysfs, then when
+			 * BCH_DO_AUTO_GC is set, garbage collection thread
+			 * will be wake up here. After moving gc, the shrunk
+			 * btree and discarded free buckets SSD space may be
+			 * helpful for following write requests.
+			 */
+			if (c->gc_after_writeback ==
+			    (BCH_ENABLE_AUTO_GC|BCH_DO_AUTO_GC)) {
+				c->gc_after_writeback &= ~BCH_DO_AUTO_GC;
+				force_wake_up_gc(c);
+			}
 		}
 
 		up_write(&dc->writeback_lock);
diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index d2b9fdbc8994..ce63be98a39d 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -11,6 +11,8 @@
 #define WRITEBACK_RATE_UPDATE_SECS_MAX		60
 #define WRITEBACK_RATE_UPDATE_SECS_DEFAULT	5
 
+#define BCH_AUTO_GC_DIRTY_THRESHOLD	50
+
 /*
  * 14 (16384ths) is chosen here as something that each backing device
  * should be a reasonable fraction of the share, and not to blow up