dm linear: eliminate linear_end_io call if CONFIG_DM_ZONED disabled

This change “dm linear: eliminate linear_end_io call if CONFIG_DM_ZONED disabled” in Linux kernel is authored by Mike Snitzer <snitzer [at] redhat.com> on Wed Oct 10 12:01:55 2018 -0400.

dm linear: eliminate linear_end_io call if CONFIG_DM_ZONED disabled

It is best to avoid any extra overhead associated with bio completion.
DM core will indirectly call a DM target's .end_io if it is defined.
In the case of DM linear, there is no need to do so (for every bio that
completes) if CONFIG_DM_ZONED is not enabled.

Avoiding an extra indirect call for every bio completion is very
important for ensuring DM linear doesn't incur more overhead that
further widens the performance gap between dm-linear and raw block
devices.

Fixes: 0be12c1c7fce7 ("dm linear: add support for zoned block devices")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit beb9caa.

There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/md/dm-linear.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index d10964d..172f6fa 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -102,6 +102,7 @@ static int linear_map(struct dm_target *ti, struct bio *bio)
 	return DM_MAPIO_REMAPPED;
 }
 
+#ifdef CONFIG_DM_ZONED
 static int linear_end_io(struct dm_target *ti, struct bio *bio,
 			 blk_status_t *error)
 {
@@ -112,6 +113,7 @@ static int linear_end_io(struct dm_target *ti, struct bio *bio,
 
 	return DM_ENDIO_DONE;
 }
+#endif
 
 static void linear_status(struct dm_target *ti, status_type_t type,
 			  unsigned status_flags, char *result, unsigned maxlen)
@@ -208,12 +210,16 @@ static size_t linear_dax_copy_to_iter(struct dm_target *ti, pgoff_t pgoff,
 static struct target_type linear_target = {
 	.name   = "linear",
 	.version = {1, 4, 0},
+#ifdef CONFIG_DM_ZONED
+	.end_io = linear_end_io,
 	.features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_ZONED_HM,
+#else
+	.features = DM_TARGET_PASSES_INTEGRITY,
+#endif
 	.module = THIS_MODULE,
 	.ctr    = linear_ctr,
 	.dtr    = linear_dtr,
 	.map    = linear_map,
-	.end_io = linear_end_io,
 	.status = linear_status,
 	.prepare_ioctl = linear_prepare_ioctl,
 	.iterate_devices = linear_iterate_devices,

The commit for this change in Linux stable tree is beb9caa (patch).

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