linux-kernel - [PATCH 4.14 070/109] dm linear: eliminate linear_end_io call if CONFIG_DM

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Date:   Tue, 16 Oct 2018 19:05:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.14 070/109] dm linear: eliminate linear_end_io call if CONFIG_DM_ZONED disabled

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@...hat.com>

commit beb9caac211c1be1bc118bb62d5cf09c4107e6a5 upstream.

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@...r.kernel.org
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -101,6 +101,7 @@ static int linear_map(struct dm_target *
 	return DM_MAPIO_REMAPPED;
 }
 
+#ifdef CONFIG_DM_ZONED
 static int linear_end_io(struct dm_target *ti, struct bio *bio,
 			 blk_status_t *error)
 {
@@ -111,6 +112,7 @@ static int linear_end_io(struct dm_targe
 
 	return DM_ENDIO_DONE;
 }
+#endif
 
 static void linear_status(struct dm_target *ti, status_type_t type,
 			  unsigned status_flags, char *result, unsigned maxlen)
@@ -187,12 +189,16 @@ static size_t linear_dax_copy_from_iter(
 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,