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Add support for DISCARD to ZVOLs.

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DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning.
It allows ZVOL clients to discard (unmap, trim) block ranges from
a ZVOL, thus optimizing disk space usage by allowing a ZVOL to
shrink instead of just grow.

We can't use zfs_space() or zfs_freesp() here, since these functions
only work on regular files, not volumes. Fortunately we can use the
low-level function dmu_free_long_range() which does exactly what we
want.

Currently the discard operation is not added to the log. That's not
a big deal since losing discard requests cannot result in data
corruption. It would however result in disk space usage higher than
it should be. Thus adding log support to zvol_discard() is probably
a good idea for a future improvement.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Etienne Dechamps
2011-09-02 15:23:12 +02:00
committed by Brian Behlendorf
parent cb2d19010d
commit 30930fba21
60 changed files with 273 additions and 0 deletions
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udev/Makefile.in
+1
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@@ -49,6 +49,7 @@ am__aclocal_m4_deps = \
$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
$(top_srcdir)/config/kernel-blk-end-request.m4 \
$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
$(top_srcdir)/config/kernel-blk-queue-discard.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 \
udev/rules.d/Makefile.in
+1
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@@ -50,6 +50,7 @@ am__aclocal_m4_deps = \
$(top_srcdir)/config/kernel-bio-rw-syncio.m4 \
$(top_srcdir)/config/kernel-blk-end-request.m4 \
$(top_srcdir)/config/kernel-blk-fetch-request.m4 \
$(top_srcdir)/config/kernel-blk-queue-discard.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 \