1 files changed, 67 insertions, 10 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 364818eef40e..912d83d8860a 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -311,6 +311,62 @@ xfs_iomap_eof_want_preallocate(
 }
 
 /*
+ * 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
  * at a single extent or less if the filesystem is near full. The closer the
@@ -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));
 
@@ -399,7 +454,6 @@ 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)
@@ -407,7 +461,10 @@ xfs_iomap_write_delay(
 
 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);