bcachefs: Scale down number of writepoints when low on space

this means we don't have to reserve space for them when calculating
filesystem capacity
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/alloc_background.c

@@ -975,6 +975,7 @@ void bch2_recalc_capacity(struct bch_fs *c)
 {
 	struct bch_dev *ca;
 	u64 capacity = 0, reserved_sectors = 0, gc_reserve;
+	unsigned bucket_size_max = 0;
 	unsigned long ra_pages = 0;
 	unsigned i, j;
 
@@ -1012,12 +1013,9 @@ void bch2_recalc_capacity(struct bch_fs *c)
 
 		dev_reserve += ca->free_inc.size;
 
-		dev_reserve += ARRAY_SIZE(c->write_points);
-
 		dev_reserve += 1;	/* btree write point */
 		dev_reserve += 1;	/* copygc write point */
 		dev_reserve += 1;	/* rebalance write point */
-		dev_reserve += WRITE_POINT_COUNT;
 
 		dev_reserve *= ca->mi.bucket_size;
 
@@ -1027,6 +1025,9 @@ void bch2_recalc_capacity(struct bch_fs *c)
 					     ca->mi.first_bucket);
 
 		reserved_sectors += dev_reserve * 2;
+
+		bucket_size_max = max_t(unsigned, bucket_size_max,
+					ca->mi.bucket_size);
 	}
 
 	gc_reserve = c->opts.gc_reserve_bytes
@@ -1039,6 +1040,8 @@ void bch2_recalc_capacity(struct bch_fs *c)
 
 	c->capacity = capacity - reserved_sectors;
 
+	c->bucket_size_max = bucket_size_max;
+
 	if (c->capacity) {
 		bch2_io_timer_add(&c->io_clock[READ],
 				 &c->bucket_clock[READ].rescale);
@@ -1330,8 +1333,6 @@ static int __bch2_fs_allocator_start(struct bch_fs *c)
 	 * invalidated on disk:
 	 */
 	if (invalidating_data) {
-		BUG();
-		pr_info("holding writes");
 		pr_debug("invalidating existing data");
 		set_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags);
 	} else {
@@ -1391,40 +1392,12 @@ int bch2_fs_allocator_start(struct bch_fs *c)
 	return bch2_alloc_write(c);
 }
 
-void bch2_fs_allocator_init(struct bch_fs *c)
+void bch2_fs_allocator_background_init(struct bch_fs *c)
 {
-	struct open_bucket *ob;
-	struct write_point *wp;
-
-	mutex_init(&c->write_points_hash_lock);
 	spin_lock_init(&c->freelist_lock);
 	bch2_bucket_clock_init(c, READ);
 	bch2_bucket_clock_init(c, WRITE);
 
-	/* open bucket 0 is a sentinal NULL: */
-	spin_lock_init(&c->open_buckets[0].lock);
-
-	for (ob = c->open_buckets + 1;
-	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets); ob++) {
-		spin_lock_init(&ob->lock);
-		c->open_buckets_nr_free++;
-
-		ob->freelist = c->open_buckets_freelist;
-		c->open_buckets_freelist = ob - c->open_buckets;
-	}
-
-	writepoint_init(&c->btree_write_point, BCH_DATA_BTREE);
-	writepoint_init(&c->rebalance_write_point, BCH_DATA_USER);
-
-	for (wp = c->write_points;
-	     wp < c->write_points + ARRAY_SIZE(c->write_points); wp++) {
-		writepoint_init(wp, BCH_DATA_USER);
-
-		wp->last_used	= sched_clock();
-		wp->write_point	= (unsigned long) wp;
-		hlist_add_head_rcu(&wp->node, writepoint_hash(c, wp->write_point));
-	}
-
 	c->pd_controllers_update_seconds = 5;
 	INIT_DELAYED_WORK(&c->pd_controllers_update, pd_controllers_update);
 }

fs/bcachefs/alloc_background.h

@@ -57,6 +57,6 @@ int bch2_dev_allocator_start(struct bch_dev *);
 
 int bch2_alloc_write(struct bch_fs *);
 int bch2_fs_allocator_start(struct bch_fs *);
-void bch2_fs_allocator_init(struct bch_fs *);
+void bch2_fs_allocator_background_init(struct bch_fs *);
 
 #endif /* _BCACHEFS_ALLOC_BACKGROUND_H */

fs/bcachefs/alloc_foreground.c

@@ -492,7 +492,7 @@ void bch2_writepoint_stop(struct bch_fs *c, struct bch_dev *ca,
 
 	mutex_lock(&wp->lock);
 	open_bucket_for_each(c, &wp->ptrs, ob, i)
-		if (ob->ptr.dev == ca->dev_idx)
+		if (!ca || ob->ptr.dev == ca->dev_idx)
 			open_bucket_free_unused(c, wp, ob);
 		else
 			ob_push(c, &ptrs, ob);
@@ -501,6 +501,15 @@ void bch2_writepoint_stop(struct bch_fs *c, struct bch_dev *ca,
 	mutex_unlock(&wp->lock);
 }
 
+static inline struct hlist_head *writepoint_hash(struct bch_fs *c,
+						 unsigned long write_point)
+{
+	unsigned hash =
+		hash_long(write_point, ilog2(ARRAY_SIZE(c->write_points_hash)));
+
+	return &c->write_points_hash[hash];
+}
+
 static struct write_point *__writepoint_find(struct hlist_head *head,
 					     unsigned long write_point)
 {
@@ -513,6 +522,53 @@ static struct write_point *__writepoint_find(struct hlist_head *head,
 	return NULL;
 }
 
+static inline bool too_many_writepoints(struct bch_fs *c, unsigned factor)
+{
+	u64 stranded	= c->write_points_nr * c->bucket_size_max;
+	u64 free	= bch2_fs_sectors_free(c, bch2_fs_usage_read(c));
+
+	return stranded * factor > free;
+}
+
+static bool try_increase_writepoints(struct bch_fs *c)
+{
+	struct write_point *wp;
+
+	if (c->write_points_nr == ARRAY_SIZE(c->write_points) ||
+	    too_many_writepoints(c, 32))
+		return false;
+
+	wp = c->write_points + c->write_points_nr++;
+	hlist_add_head_rcu(&wp->node, writepoint_hash(c, wp->write_point));
+	return true;
+}
+
+static bool try_decrease_writepoints(struct bch_fs *c,
+				     unsigned old_nr)
+{
+	struct write_point *wp;
+
+	mutex_lock(&c->write_points_hash_lock);
+	if (c->write_points_nr < old_nr) {
+		mutex_unlock(&c->write_points_hash_lock);
+		return true;
+	}
+
+	if (c->write_points_nr == 1 ||
+	    !too_many_writepoints(c, 8)) {
+		mutex_unlock(&c->write_points_hash_lock);
+		return false;
+	}
+
+	wp = c->write_points + --c->write_points_nr;
+
+	hlist_del_rcu(&wp->node);
+	mutex_unlock(&c->write_points_hash_lock);
+
+	bch2_writepoint_stop(c, NULL, wp);
+	return true;
+}
+
 static struct write_point *writepoint_find(struct bch_fs *c,
 					   unsigned long write_point)
 {
@@ -536,16 +592,22 @@ static struct write_point *writepoint_find(struct bch_fs *c,
 		mutex_unlock(&wp->lock);
 		goto restart_find;
 	}
-
+restart_find_oldest:
 	oldest = NULL;
 	for (wp = c->write_points;
-	     wp < c->write_points + ARRAY_SIZE(c->write_points);
-	     wp++)
+	     wp < c->write_points + c->write_points_nr; wp++)
 		if (!oldest || time_before64(wp->last_used, oldest->last_used))
 			oldest = wp;
 
 	mutex_lock(&oldest->lock);
 	mutex_lock(&c->write_points_hash_lock);
+	if (oldest >= c->write_points + c->write_points_nr ||
+	    try_increase_writepoints(c)) {
+		mutex_unlock(&c->write_points_hash_lock);
+		mutex_unlock(&oldest->lock);
+		goto restart_find_oldest;
+	}
+
 	wp = __writepoint_find(head, write_point);
 	if (wp && wp != oldest) {
 		mutex_unlock(&c->write_points_hash_lock);
@@ -581,10 +643,12 @@ struct write_point *bch2_alloc_sectors_start(struct bch_fs *c,
 	unsigned nr_effective = 0;
 	struct open_buckets ptrs = { .nr = 0 };
 	bool have_cache = false;
+	unsigned write_points_nr;
 	int ret = 0, i;
 
 	BUG_ON(!nr_replicas || !nr_replicas_required);
-
+retry:
+	write_points_nr = c->write_points_nr;
 	wp = writepoint_find(c, write_point.v);
 
 	if (!target || (flags & BCH_WRITE_ONLY_SPECIFIED_DEVS)) {
@@ -637,6 +701,11 @@ struct write_point *bch2_alloc_sectors_start(struct bch_fs *c,
 	wp->ptrs = ptrs;
 
 	mutex_unlock(&wp->lock);
+
+	if (ret == -ENOSPC &&
+	    try_decrease_writepoints(c, write_points_nr))
+		goto retry;
+
 	return ERR_PTR(ret);
 }
 
@@ -688,3 +757,37 @@ void bch2_alloc_sectors_done(struct bch_fs *c, struct write_point *wp)
 
 	bch2_open_buckets_put(c, &ptrs);
 }
+
+void bch2_fs_allocator_foreground_init(struct bch_fs *c)
+{
+	struct open_bucket *ob;
+	struct write_point *wp;
+
+	mutex_init(&c->write_points_hash_lock);
+	c->write_points_nr = ARRAY_SIZE(c->write_points);
+
+	/* open bucket 0 is a sentinal NULL: */
+	spin_lock_init(&c->open_buckets[0].lock);
+
+	for (ob = c->open_buckets + 1;
+	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets); ob++) {
+		spin_lock_init(&ob->lock);
+		c->open_buckets_nr_free++;
+
+		ob->freelist = c->open_buckets_freelist;
+		c->open_buckets_freelist = ob - c->open_buckets;
+	}
+
+	writepoint_init(&c->btree_write_point, BCH_DATA_BTREE);
+	writepoint_init(&c->rebalance_write_point, BCH_DATA_USER);
+
+	for (wp = c->write_points;
+	     wp < c->write_points + c->write_points_nr; wp++) {
+		writepoint_init(wp, BCH_DATA_USER);
+
+		wp->last_used	= sched_clock();
+		wp->write_point	= (unsigned long) wp;
+		hlist_add_head_rcu(&wp->node,
+				   writepoint_hash(c, wp->write_point));
+	}
+}

fs/bcachefs/alloc_foreground.h

@@ -91,15 +91,6 @@ void bch2_alloc_sectors_done(struct bch_fs *, struct write_point *);
 void bch2_writepoint_stop(struct bch_fs *, struct bch_dev *,
 			  struct write_point *);
 
-static inline struct hlist_head *writepoint_hash(struct bch_fs *c,
-						 unsigned long write_point)
-{
-	unsigned hash =
-		hash_long(write_point, ilog2(ARRAY_SIZE(c->write_points_hash)));
-
-	return &c->write_points_hash[hash];
-}
-
 static inline struct write_point_specifier writepoint_hashed(unsigned long v)
 {
 	return (struct write_point_specifier) { .v = v | 1 };
@@ -117,4 +108,6 @@ static inline void writepoint_init(struct write_point *wp,
 	wp->type = type;
 }
 
+void bch2_fs_allocator_foreground_init(struct bch_fs *);
+
 #endif /* _BCACHEFS_ALLOC_FOREGROUND_H */

fs/bcachefs/alloc_types.h

@@ -46,7 +46,9 @@ typedef FIFO(long)	alloc_fifo;
 
 /* Enough for 16 cache devices, 2 tiers and some left over for pipelining */
 #define OPEN_BUCKETS_COUNT	256
-#define WRITE_POINT_COUNT	32
+
+#define WRITE_POINT_HASH_NR	32
+#define WRITE_POINT_MAX		32
 
 struct open_bucket {
 	spinlock_t		lock;

fs/bcachefs/bcachefs.h

@@ -601,6 +601,7 @@ struct bch_fs {
 	 * and forces them to be revalidated
 	 */
 	u32			capacity_gen;
+	unsigned		bucket_size_max;
 
 	atomic64_t		sectors_available;
 
@@ -630,9 +631,10 @@ struct bch_fs {
 	struct write_point	btree_write_point;
 	struct write_point	rebalance_write_point;
 
-	struct write_point	write_points[WRITE_POINT_COUNT];
-	struct hlist_head	write_points_hash[WRITE_POINT_COUNT];
+	struct write_point	write_points[WRITE_POINT_MAX];
+	struct hlist_head	write_points_hash[WRITE_POINT_HASH_NR];
 	struct mutex		write_points_hash_lock;
+	unsigned		write_points_nr;
 
 	/* GARBAGE COLLECTION */
 	struct task_struct	*gc_thread;

fs/bcachefs/buckets.c

@@ -300,11 +300,6 @@ u64 bch2_fs_sectors_used(struct bch_fs *c, struct bch_fs_usage stats)
 	return min(c->capacity, __bch2_fs_sectors_used(c, stats));
 }
 
-static u64 bch2_fs_sectors_free(struct bch_fs *c, struct bch_fs_usage stats)
-{
-	return c->capacity - bch2_fs_sectors_used(c, stats);
-}
-
 static inline int is_unavailable_bucket(struct bucket_mark m)
 {
 	return !is_available_bucket(m);

fs/bcachefs/buckets.h

@@ -175,6 +175,12 @@ void bch2_fs_usage_apply(struct bch_fs *, struct bch_fs_usage *,
 
 u64 bch2_fs_sectors_used(struct bch_fs *, struct bch_fs_usage);
 
+static inline u64 bch2_fs_sectors_free(struct bch_fs *c,
+				       struct bch_fs_usage stats)
+{
+	return c->capacity - bch2_fs_sectors_used(c, stats);
+}
+
 static inline bool is_available_bucket(struct bucket_mark mark)
 {
 	return (!mark.owned_by_allocator &&

fs/bcachefs/super.c

@@ -524,7 +524,8 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 	for (i = 0; i < BCH_TIME_STAT_NR; i++)
 		bch2_time_stats_init(&c->times[i]);
 
-	bch2_fs_allocator_init(c);
+	bch2_fs_allocator_background_init(c);
+	bch2_fs_allocator_foreground_init(c);
 	bch2_fs_rebalance_init(c);
 	bch2_fs_quota_init(c);