Reintroduce zfs_remove() synchronous deletes

Reintroduce a slightly adapted version of the Illumos logic for
synchronous unlinks.  The basic idea here is that only files
smaller than zfs_delete_blocks (20480) blocks should be deleted
synchronously.  Unlinking larger files should be handled
asynchronously to minimize impact to the caller.

To accomplish this iput() which is responsible for calling
zfs_znode_delete() on Linux is only called in the delete_now
path.  Otherwise zfs_async_iput() is used which allows the
last reference to be dropped by a taskq thread effectively
making the removal asynchronous.

Porting notes:
- Add zfs_delete_blocks module option for performance analysis.
  The default value is DMU_MAX_DELETEBLKCNT which is the same
  as upstream.  Reducing this value means that smaller files
  will be unlinked asynchronously like large files.
- All occurrences of zfsvfs changes to zsb.

Ported-by: KernelOfTruth [email protected]
Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index e0c61ec21..f801f257b 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -718,6 +718,21 @@ Default value: \fB500,000\fR.
 .sp
 .ne 2
 .na
+\fBzfs_delete_blocks\fR (ulong)
+.ad
+.RS 12n
+This is the used to define a large file for the purposes of delete.  Files
+containing more than \fBzfs_delete_blocks\fR will be deleted asynchronously
+while smaller files are deleted synchronously.  Decreasing this value will
+reduce the time spent in an unlink(2) system call at the expense of a longer
+delay before the freed space is available.
+.sp
+Default value: \fB20,480\fR.
+.RE
+
+.sp
+.ne 2
+.na
 \fBzfs_dirty_data_max\fR (int)
 .ad
 .RS 12n