[PATCH 06/15] xfs: reorder zeroing and flushing sequence in truncate

Christoph Hellwig
2016-05-09T08:47:55Z

Currently zeroing out blocks and waiting for writeout is a bit of a mess in
truncate. This patch gives it a clear order in preparation for the iomap
path:

(1) we first wait for any direct I/O to complete to prevent any races
for it
(2) we then perform the actual zeroing, and only use the truncate_page
helpers for truncating down. The truncate up case already is
handled by the separate call to xfs_zero_eof.
(3) only then we write back dirty data, as zeroing block may cause
dirty pages when using either xfs_zero_eof or the new iomap
infrastructure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bob Peterson <rpeterso@redhat.com>
---
fs/xfs/xfs_iops.c | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index c5d4eba..1a5ca4b 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -801,20 +801,35 @@ xfs_setattr_size(
return error;

/*
+ * Wait for all direct I/O to complete.
+ */
+ inode_dio_wait(inode);
+
+ /*
* File data changes must be complete before we start the transaction to
* modify the inode. This needs to be done before joining the inode to
* the transaction because the inode cannot be unlocked once it is a
* part of the transaction.
*
- * Start with zeroing any data block beyond EOF that we may expose on
- * file extension.
+ * Start with zeroing any data beyond EOF that we may expose on file
+ * extension, or zeroing out the rest of the block on a downward
+ * truncate.
*/
if (newsize > oldsize) {
error = xfs_zero_eof(ip, newsize, oldsize, &did_zeroing);
- if (error)
- return error;
+ } else {
+ if (IS_DAX(inode)) {
+ error = dax_truncate_page(inode, newsize,
+ xfs_get_blocks_direct);
+ } else {
+ error = block_truncate_page(inode->i_mapping, newsize,
+ xfs_get_blocks);
+ }
}

+ if (error)
+ return error;
+
/*
* We are going to log the inode size change in this transaction so
* any previous writes that are beyond the on disk EOF and the new
@@ -831,9 +846,6 @@ xfs_setattr_size(
return error;
}

- /* Now wait for all direct I/O to complete. */
- inode_dio_wait(inode);
-
/*
* We've already locked out new page faults, so now we can safely remove
* pages from the page cache knowing they won't get refaulted until we
@@ -851,13 +863,6 @@ xfs_setattr_size(
* to hope that the caller sees ENOMEM and retries the truncate
* operation.
*/
- if (IS_DAX(inode))
- error = dax_truncate_page(inode, newsize, xfs_get_blocks_direct);
- else
- error = block_truncate_page(inode->i_mapping, newsize,
- xfs_get_blocks);
- if (error)
- return error;
truncate_setsize(inode, newsize);

error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);