xfs: use shifting and masking when converting rt extents, if possible

Avoid the costs of integer division (32-bit and 64-bit) if the realtime
extent size is a power of two.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index e9d317a3dafe..d7873e0360f0 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -198,6 +198,18 @@ static inline uint64_t howmany_64(uint64_t x, uint32_t y)
 	return x;
 }
 
+/* If @b is a power of 2, return log2(b).  Else return -1. */
+static inline int8_t log2_if_power2(unsigned long b)
+{
+	return is_power_of_2(b) ? ilog2(b) : -1;
+}
+
+/* If @b is a power of 2, return a mask of the lower bits, else return zero. */
+static inline unsigned long long mask64_if_power2(unsigned long b)
+{
+	return is_power_of_2(b) ? b - 1 : 0;
+}
+
 int xfs_rw_bdev(struct block_device *bdev, sector_t sector, unsigned int count,
 		char *data, enum req_op op);