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

7 files changed, 21 insertions, 0 deletions

diff --git a/include/Makefile.in b/include/Makefile.in
index 4bacc977d..da7c0018f 100644
--- a/include/Makefile.in
+++ b/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/include/linux/Makefile.in b/include/linux/Makefile.in
index cdf0e1c62..aa5651d3e 100644
--- a/include/linux/Makefile.in
+++ b/include/linux/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/include/linux/blkdev_compat.h b/include/linux/blkdev_compat.h
index bd1b2bf54..a5294ceba 100644
--- a/include/linux/blkdev_compat.h
+++ b/include/linux/blkdev_compat.h
@@ -433,6 +433,21 @@ bio_set_flags_failfast(struct block_device *bdev, int *flags)
 #endif
 
 /*
+ * 2.6.33 API change
+ * Discard granularity and alignment restrictions may now be set.  For
+ * older kernels which do not support this it is safe to skip it.
+ */
+#ifdef HAVE_DISCARD_GRANULARITY
+static inline void
+blk_queue_discard_granularity(struct request_queue *q, unsigned int dg)
+{
+	q->limits.discard_granularity = dg;
+}
+#else
+#define blk_queue_discard_granularity(x, dg)	((void)0)
+#endif /* HAVE_DISCARD_GRANULARITY */
+
+/*
  * Default Linux IO Scheduler,
  * Setting the scheduler to noop will allow the Linux IO scheduler to
  * still perform front and back merging, while leaving the request
diff --git a/include/sys/Makefile.in b/include/sys/Makefile.in
index e6e880bab..be2aec909 100644
--- a/include/sys/Makefile.in
+++ b/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/include/sys/fm/Makefile.in b/include/sys/fm/Makefile.in
index 9d2aff60b..9193af56b 100644
--- a/include/sys/fm/Makefile.in
+++ b/include/sys/fm/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/include/sys/fm/fs/Makefile.in b/include/sys/fm/fs/Makefile.in
index feac8f9fb..8d7829d83 100644
--- a/include/sys/fm/fs/Makefile.in
+++ b/include/sys/fm/fs/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/include/sys/fs/Makefile.in b/include/sys/fs/Makefile.in
index c1bff97bb..7529f0682 100644
--- a/include/sys/fs/Makefile.in
+++ b/include/sys/fs/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 \