[PATCH 2/4] xfs: push rounddown_pow_of_two() to after prealloc throttle

[Brian Foster]

The round down occurs towards the beginning of the function. Push
it down after throttling has occurred. This is to support adding
further transformations to 'alloc_blocks' that might not preserve
power-of-two alignment (and thus could lead to rounding down
multiple times).

Signed-off-by: Brian Foster <bfoster at redhat.com>
---
 fs/xfs/xfs_iomap.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index bd7c060..d381326 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -329,13 +329,11 @@ xfs_iomap_prealloc_size(
 		goto check_writeio;
 
 	/*
-	 * rounddown_pow_of_two() returns an undefined result
-	 * if we pass in alloc_blocks = 0. Hence the "+ 1" to
-	 * ensure we always pass in a non-zero value.
+	 * MAXEXTLEN is 21 bits, add one to protect against the rounddown
+	 * further down.
 	 */
-	alloc_blocks = XFS_B_TO_FSB(mp, XFS_ISIZE(ip)) + 1;
-	alloc_blocks = XFS_FILEOFF_MIN(MAXEXTLEN,
-				rounddown_pow_of_two(alloc_blocks));
+	alloc_blocks = XFS_FILEOFF_MIN(MAXEXTLEN + 1,
+				XFS_B_TO_FSB(mp, XFS_ISIZE(ip)));
 
 	xfs_icsb_sync_counters(mp, XFS_ICSB_LAZY_COUNT);
 	freesp = mp->m_sb.sb_fdblocks;
@@ -352,6 +350,8 @@ xfs_iomap_prealloc_size(
 	}
 	if (shift)
 		alloc_blocks >>= shift;
+	if (alloc_blocks)
+		alloc_blocks = rounddown_pow_of_two(alloc_blocks);
 
 check_writeio:
 	if (alloc_blocks < mp->m_writeio_blocks)
-- 
1.7.7.6