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Set zvol discard_granularity to the volblocksize.

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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 <behlendorf1@llnl.gov>
Closes #862
This commit is contained in:
Etienne Dechamps
2012-08-01 10:29:59 +02:00
committed by Brian Behlendorf
parent 9a512dca97
commit ee5fd0bb80
61 changed files with 233 additions and 0 deletions
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man/Makefile.in
+1
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@@ -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 \
man/man5/Makefile.in
+1
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@@ -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 \
man/man8/Makefile.in
+1
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@@ -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 \