Improve ZVOL queue behavior.

The Linux block device queue subsystem exposes a number of configurable
settings described in Linux block/blk-settings.c. The defaults for these
settings are tuned for hard drives, and are not optimized for ZVOLs. Proper
configuration of these options would allow upper layers (I/O scheduler) to
take better decisions about write merging and ordering.

Detailed rationale:

 - max_hw_sectors is set to unlimited (UINT_MAX). zvol_write() is able to
   handle writes of any size, so there's no reason to impose a limit. Let the
   upper layer decide.

 - max_segments and max_segment_size are set to unlimited. zvol_write() will
   copy the requests' contents into a dbuf anyway, so the number and size of
   the segments are irrelevant. Let the upper layer decide.

 - physical_block_size and io_opt are set to the ZVOL's block size. This
   has the potential to somewhat alleviate issue #361 for ZVOLs, by warning
   the upper layers that writes smaller than the volume's block size will be
   slow.

 - The NONROT flag is set to indicate this isn't a rotational device.
   Although the backing zpool might be composed of rotational devices, the
   resulting ZVOL often doesn't exhibit the same behavior due to the COW
   mechanisms used by ZFS. Setting this flag will prevent upper layers from
   making useless decisions (such as reordering writes) based on incorrect
   assumptions about the behavior of the ZVOL.

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

5 files changed, 25 insertions, 0 deletions

diff --git a/scripts/Makefile.in b/scripts/Makefile.in
index e762912fe..f09668560 100644
--- a/scripts/Makefile.in
+++ b/scripts/Makefile.in
@@ -51,6 +51,11 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-segments.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-nonrot.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-physical-block-size.m4 \
 	$(top_srcdir)/config/kernel-blk-requeue-request.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-bytes.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-pos.m4 \
diff --git a/scripts/zpios-profile/Makefile.in b/scripts/zpios-profile/Makefile.in
index 538416193..e50a0a4af 100644
--- a/scripts/zpios-profile/Makefile.in
+++ b/scripts/zpios-profile/Makefile.in
@@ -51,6 +51,11 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-segments.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-nonrot.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-physical-block-size.m4 \
 	$(top_srcdir)/config/kernel-blk-requeue-request.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-bytes.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-pos.m4 \
diff --git a/scripts/zpios-test/Makefile.in b/scripts/zpios-test/Makefile.in
index ec5f01e72..46e7e0860 100644
--- a/scripts/zpios-test/Makefile.in
+++ b/scripts/zpios-test/Makefile.in
@@ -51,6 +51,11 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-segments.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-nonrot.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-physical-block-size.m4 \
 	$(top_srcdir)/config/kernel-blk-requeue-request.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-bytes.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-pos.m4 \
diff --git a/scripts/zpool-config/Makefile.in b/scripts/zpool-config/Makefile.in
index f60ecf891..33ceab9a1 100644
--- a/scripts/zpool-config/Makefile.in
+++ b/scripts/zpool-config/Makefile.in
@@ -51,6 +51,11 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-segments.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-nonrot.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-physical-block-size.m4 \
 	$(top_srcdir)/config/kernel-blk-requeue-request.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-bytes.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-pos.m4 \
diff --git a/scripts/zpool-layout/Makefile.in b/scripts/zpool-layout/Makefile.in
index 61b1b06bc..6e45dbbc3 100644
--- a/scripts/zpool-layout/Makefile.in
+++ b/scripts/zpool-layout/Makefile.in
@@ -51,6 +51,11 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-blk-end-request.m4 \
 	$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
 	$(top_srcdir)/config/kernel-blk-queue-flush.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-io-opt.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-hw-sectors.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-max-segments.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-nonrot.m4 \
+	$(top_srcdir)/config/kernel-blk-queue-physical-block-size.m4 \
 	$(top_srcdir)/config/kernel-blk-requeue-request.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-bytes.m4 \
 	$(top_srcdir)/config/kernel-blk-rq-pos.m4 \