xfs: add EOFBLOCKS inode tagging/untagging

Add the XFS_ICI_EOFBLOCKS_TAG inode tag to identify inodes with
speculatively preallocated blocks beyond EOF. An inode is tagged
when speculative preallocation occurs and untagged either via
truncate down or when post-EOF blocks are freed via release or
reclaim.

The tag management is intentionally not aggressive to prefer
simplicity over the complexity of handling all the corner cases
under which post-EOF blocks could be freed (i.e., forward
truncation, fallocate, write error conditions, etc.). This means
that a tagged inode may or may not have post-EOF blocks after a
period of time. The tag is eventually cleared when the inode is
released or reclaimed.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a066cf1766ab..add06b4e9a63 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -41,6 +41,7 @@
 #include "xfs_utils.h"
 #include "xfs_iomap.h"
 #include "xfs_trace.h"
+#include "xfs_icache.h"
 
 
 #define XFS_WRITEIO_ALIGN(mp,off)       (((off) >> mp->m_writeio_log) \
@@ -450,6 +451,13 @@ retry:
         if (!(imap[0].br_startblock || XFS_IS_REALTIME_INODE(ip)))
                 return xfs_alert_fsblock_zero(ip, &imap[0]);
 
+        /*
+         * Tag the inode as speculatively preallocated so we can reclaim this
+         * space on demand, if necessary.
+         */
+        if (prealloc)
+                xfs_inode_set_eofblocks_tag(ip);
+
         *ret_imap = imap[0];
         return 0;
 }