bcachefs: Refactor rebalance_pred function

Before, the logic for if we should move an extent was duplicated
somewhat, in both rebalance_add_key() and rebalance_pred(); this
centralizes that in __rebalance_pred()

This is prep work for a patch that enables marking data as
incompressible.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/rebalance.c

@@ -17,50 +17,51 @@
 #include <linux/kthread.h>
 #include <linux/sched/cputime.h>
 
-static inline bool rebalance_ptr_pred(struct bch_fs *c,
-				      struct extent_ptr_decoded p,
-				      struct bch_io_opts *io_opts)
+/*
+ * Check if an extent should be moved:
+ * returns -1 if it should not be moved, or
+ * device of pointer that should be moved, if known, or INT_MAX if unknown
+ */
+static int __bch2_rebalance_pred(struct bch_fs *c,
+				 struct bkey_s_c k,
+				 struct bch_io_opts *io_opts)
 {
-	if (io_opts->background_target &&
-	    !bch2_dev_in_target(c, p.ptr.dev, io_opts->background_target) &&
-	    !p.ptr.cached)
-		return true;
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	const union bch_extent_entry *entry;
+	struct extent_ptr_decoded p;
+
+	if (io_opts->background_compression)
+		bkey_for_each_ptr_decode(k.k, ptrs, p, entry)
+			if (!p.ptr.cached &&
+			    p.crc.compression_type !=
+			    bch2_compression_opt_to_type[io_opts->background_compression])
+				return p.ptr.dev;
 
-	if (io_opts->background_compression &&
-	    p.crc.compression_type !=
-	    bch2_compression_opt_to_type[io_opts->background_compression])
-		return true;
+	if (io_opts->background_target)
+		bkey_for_each_ptr_decode(k.k, ptrs, p, entry)
+			if (!p.ptr.cached &&
+			    !bch2_dev_in_target(c, p.ptr.dev, io_opts->background_target))
+				return p.ptr.dev;
 
-	return false;
+	return -1;
 }
 
 void bch2_rebalance_add_key(struct bch_fs *c,
 			    struct bkey_s_c k,
 			    struct bch_io_opts *io_opts)
 {
-	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
-	const union bch_extent_entry *entry;
-	struct extent_ptr_decoded p;
+	atomic64_t *counter;
+	int dev;
 
-	if (!io_opts->background_target &&
-	    !io_opts->background_compression)
+	dev = __bch2_rebalance_pred(c, k, io_opts);
+	if (dev < 0)
 		return;
 
-	bkey_for_each_ptr_decode(k.k, ptrs, p, entry)
-		if (rebalance_ptr_pred(c, p, io_opts)) {
-			struct bch_dev *ca = bch_dev_bkey_exists(c, p.ptr.dev);
+	counter = dev < INT_MAX
+		? &bch_dev_bkey_exists(c, dev)->rebalance_work
+		: &c->rebalance.work_unknown_dev;
 
-			if (atomic64_add_return(p.crc.compressed_size,
-						&ca->rebalance_work) ==
-			    p.crc.compressed_size)
-				rebalance_wakeup(c);
-		}
-}
-
-void bch2_rebalance_add_work(struct bch_fs *c, u64 sectors)
-{
-	if (atomic64_add_return(sectors, &c->rebalance.work_unknown_dev) ==
-	    sectors)
+	if (atomic64_add_return(k.k->size, counter) == k.k->size)
 		rebalance_wakeup(c);
 }
 
@@ -69,26 +70,20 @@ static enum data_cmd rebalance_pred(struct bch_fs *c, void *arg,
 				    struct bch_io_opts *io_opts,
 				    struct data_opts *data_opts)
 {
-	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
-	const union bch_extent_entry *entry;
-	struct extent_ptr_decoded p;
-	unsigned nr_replicas = 0;
-
-	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
-		nr_replicas += !p.ptr.cached;
-
-		if (rebalance_ptr_pred(c, p, io_opts))
-			goto found;
+	if (__bch2_rebalance_pred(c, k, io_opts) >= 0) {
+		data_opts->target		= io_opts->background_target;
+		data_opts->btree_insert_flags	= 0;
+		return DATA_ADD_REPLICAS;
+	} else {
+		return DATA_SKIP;
 	}
+}
 
-	if (nr_replicas < io_opts->data_replicas)
-		goto found;
-
-	return DATA_SKIP;
-found:
-	data_opts->target		= io_opts->background_target;
-	data_opts->btree_insert_flags	= 0;
-	return DATA_ADD_REPLICAS;
+void bch2_rebalance_add_work(struct bch_fs *c, u64 sectors)
+{
+	if (atomic64_add_return(sectors, &c->rebalance.work_unknown_dev) ==
+	    sectors)
+		rebalance_wakeup(c);
 }
 
 struct rebalance_work {