---

yaml
---
r: 352941
b: refs/heads/master
c: a1e16c2
h: refs/heads/master
i:
  352939: 8d3cd03
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 311f08acde635e4e5ccea9b9d8c856cc2e0ced95
+refs/heads/master: a1e16c26660b301cc8423185924cf1b0b16ea92b

trunk/fs/xfs/xfs_iomap.c

@@ -310,6 +310,62 @@ xfs_iomap_eof_want_preallocate(
 	return 0;
 }
 
+/*
+ * Determine the initial size of the preallocation. We are beyond the current
+ * EOF here, but we need to take into account whether this is a sparse write or
+ * an extending write when determining the preallocation size.  Hence we need to
+ * look up the extent that ends at the current write offset and use the result
+ * to determine the preallocation size.
+ *
+ * If the extent is a hole, then preallocation is essentially disabled.
+ * Otherwise we take the size of the preceeding data extent as the basis for the
+ * preallocation size. If the size of the extent is greater than half the
+ * maximum extent length, then use the current offset as the basis. This ensures
+ * that for large files the preallocation size always extends to MAXEXTLEN
+ * rather than falling short due to things like stripe unit/width alignment of
+ * real extents.
+ */
+STATIC int
+xfs_iomap_eof_prealloc_initial_size(
+	struct xfs_mount	*mp,
+	struct xfs_inode	*ip,
+	xfs_off_t		offset,
+	xfs_bmbt_irec_t		*imap,
+	int			nimaps)
+{
+	xfs_fileoff_t   start_fsb;
+	int		imaps = 1;
+	int		error;
+
+	ASSERT(nimaps >= imaps);
+
+	/* if we are using a specific prealloc size, return now */
+	if (mp->m_flags & XFS_MOUNT_DFLT_IOSIZE)
+		return 0;
+
+	/*
+	 * As we write multiple pages, the offset will always align to the
+	 * start of a page and hence point to a hole at EOF. i.e. if the size is
+	 * 4096 bytes, we only have one block at FSB 0, but XFS_B_TO_FSB(4096)
+	 * will return FSB 1. Hence if there are blocks in the file, we want to
+	 * point to the block prior to the EOF block and not the hole that maps
+	 * directly at @offset.
+	 */
+	start_fsb = XFS_B_TO_FSB(mp, offset);
+	if (start_fsb)
+		start_fsb--;
+	error = xfs_bmapi_read(ip, start_fsb, 1, imap, &imaps, XFS_BMAPI_ENTIRE);
+	if (error)
+		return 0;
+
+	ASSERT(imaps == 1);
+	if (imap[0].br_startblock == HOLESTARTBLOCK)
+		return 0;
+	if (imap[0].br_blockcount <= (MAXEXTLEN >> 1))
+		return imap[0].br_blockcount;
+	return XFS_B_TO_FSB(mp, offset);
+}
+
 /*
  * If we don't have a user specified preallocation size, dynamically increase
  * the preallocation size as the size of the file grows. Cap the maximum size
@@ -319,20 +375,19 @@ xfs_iomap_eof_want_preallocate(
 STATIC xfs_fsblock_t
 xfs_iomap_prealloc_size(
 	struct xfs_mount	*mp,
-	struct xfs_inode	*ip)
+	struct xfs_inode	*ip,
+	xfs_off_t		offset,
+	struct xfs_bmbt_irec	*imap,
+	int			nimaps)
 {
 	xfs_fsblock_t		alloc_blocks = 0;
 
-	if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE)) {
+	alloc_blocks = xfs_iomap_eof_prealloc_initial_size(mp, ip, offset,
+							   imap, nimaps);
+	if (alloc_blocks > 0) {
 		int shift = 0;
 		int64_t freesp;
 
-		/*
-		 * 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.
-		 */
-		alloc_blocks = XFS_B_TO_FSB(mp, XFS_ISIZE(ip)) + 1;
 		alloc_blocks = XFS_FILEOFF_MIN(MAXEXTLEN,
 					rounddown_pow_of_two(alloc_blocks));
 
@@ -399,15 +454,17 @@ xfs_iomap_write_delay(
 	extsz = xfs_get_extsz_hint(ip);
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);
 
-
 	error = xfs_iomap_eof_want_preallocate(mp, ip, offset, count,
 				imap, XFS_WRITE_IMAPS, &prealloc);
 	if (error)
 		return error;
 
 retry:
 	if (prealloc) {
-		xfs_fsblock_t	alloc_blocks = xfs_iomap_prealloc_size(mp, ip);
+		xfs_fsblock_t	alloc_blocks;
+
+		alloc_blocks = xfs_iomap_prealloc_size(mp, ip, offset, imap,
+						       XFS_WRITE_IMAPS);
 
 		aligned_offset = XFS_WRITEIO_ALIGN(mp, (offset + count - 1));
 		ioalign = XFS_B_TO_FSBT(mp, aligned_offset);