bcachefs: Switch gc bucket array to a genradix

A user with a 30 tb device is overflowing the INT_MAX limit on vmalloc
allocations...
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -542,7 +542,7 @@ struct bch_dev {
 	 * gc_gens_lock, for device resize - holding any is sufficient for
 	 * access: Or rcu_read_lock(), but only for dev_ptr_stale():
 	 */
-	struct bucket_array __rcu *buckets_gc;
+	GENRADIX(struct bucket)	buckets_gc;
 	struct bucket_gens __rcu *bucket_gens;
 	u8			*oldest_gen;
 	unsigned long		*buckets_nouse;

fs/bcachefs/btree_gc.c

@@ -753,10 +753,8 @@ static void bch2_gc_free(struct bch_fs *c)
 	genradix_free(&c->reflink_gc_table);
 	genradix_free(&c->gc_stripes);
 
-	for_each_member_device(c, ca) {
-		kvfree(rcu_dereference_protected(ca->buckets_gc, 1));
-		ca->buckets_gc = NULL;
-	}
+	for_each_member_device(c, ca)
+		genradix_free(&ca->buckets_gc);
 }
 
 static int bch2_gc_start(struct bch_fs *c)
@@ -910,20 +908,12 @@ static int bch2_gc_alloc_start(struct bch_fs *c)
 	int ret = 0;
 
 	for_each_member_device(c, ca) {
-		struct bucket_array *buckets = kvmalloc(sizeof(struct bucket_array) +
-				ca->mi.nbuckets * sizeof(struct bucket),
-				GFP_KERNEL|__GFP_ZERO);
-		if (!buckets) {
+		ret = genradix_prealloc(&ca->buckets_gc, ca->mi.nbuckets, GFP_KERNEL);
+		if (ret) {
 			bch2_dev_put(ca);
 			ret = -BCH_ERR_ENOMEM_gc_alloc_start;
 			break;
 		}
-
-		buckets->first_bucket	= ca->mi.first_bucket;
-		buckets->nbuckets	= ca->mi.nbuckets;
-		buckets->nbuckets_minus_first =
-			buckets->nbuckets - buckets->first_bucket;
-		rcu_assign_pointer(ca->buckets_gc, buckets);
 	}
 
 	bch_err_fn(c, ret);

fs/bcachefs/buckets.h

@@ -80,22 +80,9 @@ static inline void bucket_lock(struct bucket *b)
 			 TASK_UNINTERRUPTIBLE);
 }
 
-static inline struct bucket_array *gc_bucket_array(struct bch_dev *ca)
-{
-	return rcu_dereference_check(ca->buckets_gc,
-				     !ca->fs ||
-				     percpu_rwsem_is_held(&ca->fs->mark_lock) ||
-				     lockdep_is_held(&ca->fs->state_lock) ||
-				     lockdep_is_held(&ca->bucket_lock));
-}
-
 static inline struct bucket *gc_bucket(struct bch_dev *ca, size_t b)
 {
-	struct bucket_array *buckets = gc_bucket_array(ca);
-
-	if (b - buckets->first_bucket >= buckets->nbuckets_minus_first)
-		return NULL;
-	return buckets->b + b;
+	return genradix_ptr(&ca->buckets_gc, b);
 }
 
 static inline struct bucket_gens *bucket_gens(struct bch_dev *ca)

fs/bcachefs/buckets_types.h

@@ -19,14 +19,6 @@ struct bucket {
 	u32			stripe_sectors;
 } __aligned(sizeof(long));
 
-struct bucket_array {
-	struct rcu_head		rcu;
-	u16			first_bucket;
-	size_t			nbuckets;
-	size_t			nbuckets_minus_first;
-	struct bucket		b[] __counted_by(nbuckets);
-};
-
 struct bucket_gens {
 	struct rcu_head		rcu;
 	u16			first_bucket;