diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index f11123079fe0..41adcd1546f1 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -329,12 +329,13 @@ void bch_data_insert(struct closure *cl)
 	bch_data_insert_start(cl);
 }
 
-/* Congested? */
-
-unsigned int bch_get_congested(struct cache_set *c)
+/*
+ * Congested?  Return 0 (not congested) or the limit (in sectors)
+ * beyond which we should bypass the cache due to congestion.
+ */
+unsigned int bch_get_congested(const struct cache_set *c)
 {
 	int i;
-	long rand;
 
 	if (!c->congested_read_threshold_us &&
 	    !c->congested_write_threshold_us)
@@ -353,8 +354,7 @@ unsigned int bch_get_congested(struct cache_set *c)
 	if (i > 0)
 		i = fract_exp_two(i, 6);
 
-	rand = get_random_int();
-	i -= bitmap_weight(&rand, BITS_PER_LONG);
+	i -= hweight32(get_random_u32());
 
 	return i > 0 ? i : 1;
 }
@@ -376,7 +376,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
 {
 	struct cache_set *c = dc->disk.c;
 	unsigned int mode = cache_mode(dc);
-	unsigned int sectors, congested = bch_get_congested(c);
+	unsigned int sectors, congested;
 	struct task_struct *task = current;
 	struct io *i;
 
@@ -412,6 +412,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
 			goto rescale;
 	}
 
+	congested = bch_get_congested(c);
 	if (!congested && !dc->sequential_cutoff)
 		goto rescale;
 
diff --git a/drivers/md/bcache/request.h b/drivers/md/bcache/request.h
index 721bf336ed1a..c64dbd7a91aa 100644
--- a/drivers/md/bcache/request.h
+++ b/drivers/md/bcache/request.h
@@ -33,7 +33,7 @@ struct data_insert_op {
 	BKEY_PADDED(replace_key);
 };
 
-unsigned int bch_get_congested(struct cache_set *c);
+unsigned int bch_get_congested(const struct cache_set *c);
 void bch_data_insert(struct closure *cl);
 
 void bch_cached_dev_request_init(struct cached_dev *dc);
diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h
index 00aab6abcfe4..1fbced94e4cc 100644
--- a/drivers/md/bcache/util.h
+++ b/drivers/md/bcache/util.h
@@ -560,17 +560,29 @@ static inline uint64_t bch_crc64_update(uint64_t crc,
 	return crc;
 }
 
-/* Does linear interpolation between powers of two */
+/*
+ * A stepwise-linear pseudo-exponential.  This returns 1 << (x >>
+ * frac_bits), with the less-significant bits filled in by linear
+ * interpolation.
+ *
+ * This can also be interpreted as a floating-point number format,
+ * where the low frac_bits are the mantissa (with implicit leading
+ * 1 bit), and the more significant bits are the exponent.
+ * The return value is 1.mantissa * 2^exponent.
+ *
+ * The way this is used, fract_bits is 6 and the largest possible
+ * input is CONGESTED_MAX-1 = 1023 (exponent 16, mantissa 0x1.fc),
+ * so the maximum output is 0x1fc00.
+ */
 static inline unsigned int fract_exp_two(unsigned int x,
 					 unsigned int fract_bits)
 {
-	unsigned int fract = x & ~(~0 << fract_bits);
+	unsigned int mantissa = 1 << fract_bits;	/* Implicit bit */
 
-	x >>= fract_bits;
-	x   = 1 << x;
-	x  += (x * fract) >> fract_bits;
-
-	return x;
+	mantissa += x & (mantissa - 1);
+	x >>= fract_bits;	/* The exponent */
+	/* Largest intermediate value 0x7f0000 */
+	return mantissa << x >> fract_bits;
 }
 
 void bch_bio_map(struct bio *bio, void *base);