Set zvol discard_granularity to the volblocksize.

Currently, zvols have a discard granularity set to 0, which suggests to
the upper layer that discard requests of arbirarily small size and
alignment can be made efficiently.

In practice however, ZFS does not handle unaligned discard requests
efficiently: indeed, it is unable to free a part of a block. It will
write zeros to the specified range instead, which is both useless and
inefficient (see dnode_free_range).

With this patch, zvol block devices expose volblocksize as their discard
granularity, so the upper layer is aware that it's not supposed to send
discard requests smaller than volblocksize.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #862

8 files changed, 8 insertions, 0 deletions

diff --git a/lib/libspl/include/Makefile.in b/lib/libspl/include/Makefile.in
index 0c6fdcf69..b81c3dbe8 100644
--- a/lib/libspl/include/Makefile.in
+++ b/lib/libspl/include/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/ia32/Makefile.in b/lib/libspl/include/ia32/Makefile.in
index 02186ac39..23ffb4dc1 100644
--- a/lib/libspl/include/ia32/Makefile.in
+++ b/lib/libspl/include/ia32/Makefile.in
@@ -68,6 +68,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/ia32/sys/Makefile.in b/lib/libspl/include/ia32/sys/Makefile.in
index f9e0236bc..2b2c230f9 100644
--- a/lib/libspl/include/ia32/sys/Makefile.in
+++ b/lib/libspl/include/ia32/sys/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/rpc/Makefile.in b/lib/libspl/include/rpc/Makefile.in
index b601bc125..3752b74df 100644
--- a/lib/libspl/include/rpc/Makefile.in
+++ b/lib/libspl/include/rpc/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/sys/Makefile.in b/lib/libspl/include/sys/Makefile.in
index 8258f0fe0..fec69dfe7 100644
--- a/lib/libspl/include/sys/Makefile.in
+++ b/lib/libspl/include/sys/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/sys/dktp/Makefile.in b/lib/libspl/include/sys/dktp/Makefile.in
index 9ea3a27c2..3932adcba 100644
--- a/lib/libspl/include/sys/dktp/Makefile.in
+++ b/lib/libspl/include/sys/dktp/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/sys/sysevent/Makefile.in b/lib/libspl/include/sys/sysevent/Makefile.in
index 62b876137..7d784f360 100644
--- a/lib/libspl/include/sys/sysevent/Makefile.in
+++ b/lib/libspl/include/sys/sysevent/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \
diff --git a/lib/libspl/include/util/Makefile.in b/lib/libspl/include/util/Makefile.in
index cf37f1639..e32a340d2 100644
--- a/lib/libspl/include/util/Makefile.in
+++ b/lib/libspl/include/util/Makefile.in
@@ -70,6 +70,7 @@ am__aclocal_m4_deps =  \
 	$(top_srcdir)/config/kernel-create-umode-t.m4 \
 	$(top_srcdir)/config/kernel-d-make-root.m4 \
 	$(top_srcdir)/config/kernel-d-obtain-alias.m4 \
+	$(top_srcdir)/config/kernel-discard-granularity.m4 \
 	$(top_srcdir)/config/kernel-encode-fh-inode.m4 \
 	$(top_srcdir)/config/kernel-evict-inode.m4 \
 	$(top_srcdir)/config/kernel-fallocate.m4 \