X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=fs%2Fxfs%2Fxfs_iomap.c;h=67f22b2b44b3c41c51ce3ac6c1f911f5db47b181;hb=9e88ba4e45ecad2425c4cc4e0861a26f4e36c6da;hp=7edcde691d1a2539e340db2e83769ad12188e6e6;hpb=95dfec6ae1cb8c03406aac612a5642cbddb676b3;p=linux-2.6

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 7edcde691d..67f22b2b44 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -889,6 +889,16 @@ xfs_iomap_write_unwritten(
 	count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
 	count_fsb = (xfs_filblks_t)(count_fsb - offset_fsb);
 
+	/*
+	 * Reserve enough blocks in this transaction for two complete extent
+	 * btree splits.  We may be converting the middle part of an unwritten
+	 * extent and in this case we will insert two new extents in the btree
+	 * each of which could cause a full split.
+	 *
+	 * This reservation amount will be used in the first call to
+	 * xfs_bmbt_split() to select an AG with enough space to satisfy the
+	 * rest of the operation.
+	 */
 	resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0) << 1;
 
 	do {