Add TRIM support

UNMAP/TRIM support is a frequently-requested feature to help
prevent performance from degrading on SSDs and on various other
SAN-like storage back-ends.  By issuing UNMAP/TRIM commands for
sectors which are no longer allocated the underlying device can
often more efficiently manage itself.

This TRIM implementation is modeled on the `zpool initialize`
feature which writes a pattern to all unallocated space in the
pool.  The new `zpool trim` command uses the same vdev_xlate()
code to calculate what sectors are unallocated, the same per-
vdev TRIM thread model and locking, and the same basic CLI for
a consistent user experience.  The core difference is that
instead of writing a pattern it will issue UNMAP/TRIM commands
for those extents.

The zio pipeline was updated to accommodate this by adding a new
ZIO_TYPE_TRIM type and associated spa taskq.  This new type makes
is straight forward to add the platform specific TRIM/UNMAP calls
to vdev_disk.c and vdev_file.c.  These new ZIO_TYPE_TRIM zios are
handled largely the same way as ZIO_TYPE_READs or ZIO_TYPE_WRITEs.
This makes it possible to largely avoid changing the pipieline,
one exception is that TRIM zio's may exceed the 16M block size
limit since they contain no data.

In addition to the manual `zpool trim` command, a background
automatic TRIM was added and is controlled by the 'autotrim'
property.  It relies on the exact same infrastructure as the
manual TRIM.  However, instead of relying on the extents in a
metaslab's ms_allocatable range tree, a ms_trim tree is kept
per metaslab.  When 'autotrim=on', ranges added back to the
ms_allocatable tree are also added to the ms_free tree.  The
ms_free tree is then periodically consumed by an autotrim
thread which systematically walks a top level vdev's metaslabs.

Since the automatic TRIM will skip ranges it considers too small
there is value in occasionally running a full `zpool trim`.  This
may occur when the freed blocks are small and not enough time
was allowed to aggregate them.  An automatic TRIM and a manual
`zpool trim` may be run concurrently, in which case the automatic
TRIM will yield to the manual TRIM.

Reviewed-by: Jorgen Lundman <[email protected]>
Reviewed-by: Tim Chase <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Contributions-by: Saso Kiselkov <[email protected]>
Contributions-by: Tim Chase <[email protected]>
Contributions-by: Chunwei Chen <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #8419 
Closes #598 

1 files changed, 19 insertions, 6 deletions

diff --git a/include/sys/metaslab_impl.h b/include/sys/metaslab_impl.h
index 676c5dd46..ca1104c14 100644
--- a/include/sys/metaslab_impl.h
+++ b/include/sys/metaslab_impl.h
@@ -69,7 +69,7 @@ typedef enum trace_alloc_type {
 	TRACE_ENOSPC		= -6ULL,
 	TRACE_CONDENSING	= -7ULL,
 	TRACE_VDEV_ERROR	= -8ULL,
-	TRACE_INITIALIZING	= -9ULL
+	TRACE_DISABLED		= -9ULL,
 } trace_alloc_type_t;
 
 #define	METASLAB_WEIGHT_PRIMARY		(1ULL << 63)
@@ -272,10 +272,10 @@ struct metaslab_group {
 	uint64_t		mg_fragmentation;
 	uint64_t		mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
 
-	int			mg_ms_initializing;
-	boolean_t		mg_initialize_updating;
-	kmutex_t		mg_ms_initialize_lock;
-	kcondvar_t		mg_ms_initialize_cv;
+	int			mg_ms_disabled;
+	boolean_t		mg_disabled_updating;
+	kmutex_t		mg_ms_disabled_lock;
+	kcondvar_t		mg_ms_disabled_cv;
 };
 
 /*
@@ -389,11 +389,24 @@ struct metaslab {
 	range_tree_t	*ms_defer[TXG_DEFER_SIZE];
 	range_tree_t	*ms_checkpointing; /* to add to the checkpoint */
 
+	/*
+	 * The ms_trim tree is the set of allocatable segments which are
+	 * eligible for trimming. (When the metaslab is loaded, it's a
+	 * subset of ms_allocatable.)  It's kept in-core as long as the
+	 * autotrim property is set and is not vacated when the metaslab
+	 * is unloaded.  Its purpose is to aggregate freed ranges to
+	 * facilitate efficient trimming.
+	 */
+	range_tree_t	*ms_trim;
+
 	boolean_t	ms_condensing;	/* condensing? */
 	boolean_t	ms_condense_wanted;
 	uint64_t	ms_condense_checked_txg;
 
-	uint64_t	ms_initializing; /* leaves initializing this ms */
+	/*
+	 * The number of consumers which have disabled the metaslab.
+	 */
+	uint64_t	ms_disabled;
 
 	/*
 	 * We must always hold the ms_lock when modifying ms_loaded