Trim L2ARC

The l2arc_evict() function is responsible for evicting buffers which
reference the next bytes of the L2ARC device to be overwritten. Teach
this function to additionally TRIM that vdev space before it is
overwritten if the device has been filled with data. This is done by
vdev_trim_simple() which trims by issuing a new type of TRIM,
TRIM_TYPE_SIMPLE.

We also implement a "Trim Ahead" feature. It is a zfs module parameter,
expressed in % of the current write size. This trims ahead of the
current write size. A minimum of 64MB will be trimmed. The default is 0
which disables TRIM on L2ARC as it can put significant stress to
underlying storage devices. To enable TRIM on L2ARC we set
l2arc_trim_ahead > 0.

We also implement TRIM of the whole cache device upon addition to a
pool, pool creation or when the header of the device is invalid upon
importing a pool or onlining a cache device. This is dependent on
l2arc_trim_ahead > 0. TRIM of the whole device is done with
TRIM_TYPE_MANUAL so that its status can be monitored by zpool status -t.
We save the TRIM state for the whole device and the time of completion
on-disk in the header, and restore these upon L2ARC rebuild so that
zpool status -t can correctly report them. Whole device TRIM is done
asynchronously so that the user can export of the pool or remove the
cache device while it is trimming (ie if it is too slow).

We do not TRIM the whole device if persistent L2ARC has been disabled by
l2arc_rebuild_enabled = 0 because we may not want to lose all cached
buffers (eg we may want to import the pool with
l2arc_rebuild_enabled = 0 only once because of memory pressure). If
persistent L2ARC has been disabled by setting the module parameter
l2arc_rebuild_blocks_min_l2size to a value greater than the size of the
cache device then the whole device is trimmed upon creation or import of
a pool if l2arc_trim_ahead > 0.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Adam D. Moss <[email protected]>
Signed-off-by: George Amanakis <[email protected]>
Closes #9713
Closes #9789 
Closes #10224

4 files changed, 24 insertions, 2 deletions

diff --git a/include/sys/arc_impl.h b/include/sys/arc_impl.h
index e8c944ce8..5724db0a5 100644
--- a/include/sys/arc_impl.h
+++ b/include/sys/arc_impl.h
@@ -240,7 +240,14 @@ typedef struct l2arc_dev_hdr_phys {
 	 */
 	uint64_t	dh_lb_asize;		/* mirror of l2ad_lb_asize */
 	uint64_t	dh_lb_count;		/* mirror of l2ad_lb_count */
-	const uint64_t		dh_pad[32];	/* pad to 512 bytes */
+	/*
+	 * Mirrors of vdev_trim_action_time and vdev_trim_state, used to
+	 * display when the cache device was fully trimmed for the last
+	 * time.
+	 */
+	uint64_t		dh_trim_action_time;
+	uint64_t		dh_trim_state;
+	const uint64_t		dh_pad[30];	/* pad to 512 bytes */
 	zio_eck_t		dh_tail;
 } l2arc_dev_hdr_phys_t;
 CTASSERT_GLOBAL(sizeof (l2arc_dev_hdr_phys_t) == SPA_MINBLOCKSIZE);
@@ -399,6 +406,7 @@ typedef struct l2arc_dev {
 	 * Number of log blocks present on the device.
 	 */
 	zfs_refcount_t		l2ad_lb_count;
+	boolean_t		l2ad_trim_all; /* TRIM whole device */
 } l2arc_dev_t;
 
 /*
@@ -902,6 +910,10 @@ extern int param_set_arc_int(ZFS_MODULE_PARAM_ARGS);
 boolean_t l2arc_log_blkptr_valid(l2arc_dev_t *dev,
     const l2arc_log_blkptr_t *lbp);
 
+/* used in vdev_trim.c */
+void l2arc_dev_hdr_update(l2arc_dev_t *dev);
+l2arc_dev_t *l2arc_vdev_get(vdev_t *vd);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/include/sys/spa.h b/include/sys/spa.h
index a03319e2b..5806dda41 100644
--- a/include/sys/spa.h
+++ b/include/sys/spa.h
@@ -745,6 +745,7 @@ typedef enum {
 typedef enum trim_type {
 	TRIM_TYPE_MANUAL = 0,
 	TRIM_TYPE_AUTO = 1,
+	TRIM_TYPE_SIMPLE = 2
 } trim_type_t;
 
 /* state manipulation functions */
@@ -788,6 +789,7 @@ extern int bpobj_enqueue_free_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx);
 #define	SPA_ASYNC_TRIM_RESTART			0x200
 #define	SPA_ASYNC_AUTOTRIM_RESTART		0x400
 #define	SPA_ASYNC_L2CACHE_REBUILD		0x800
+#define	SPA_ASYNC_L2CACHE_TRIM			0x1000
 
 /*
  * Controls the behavior of spa_vdev_remove().
@@ -940,6 +942,12 @@ typedef struct spa_iostats {
 	kstat_named_t	autotrim_bytes_skipped;
 	kstat_named_t	autotrim_extents_failed;
 	kstat_named_t	autotrim_bytes_failed;
+	kstat_named_t	simple_trim_extents_written;
+	kstat_named_t	simple_trim_bytes_written;
+	kstat_named_t	simple_trim_extents_skipped;
+	kstat_named_t	simple_trim_bytes_skipped;
+	kstat_named_t	simple_trim_extents_failed;
+	kstat_named_t	simple_trim_bytes_failed;
 } spa_iostats_t;
 
 extern void spa_stats_init(spa_t *spa);
diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h
index 96546ac35..56407a191 100644
--- a/include/sys/vdev_impl.h
+++ b/include/sys/vdev_impl.h
@@ -301,7 +301,7 @@ struct vdev {
 	uint64_t	vdev_initialize_inflight;
 	kmutex_t	vdev_trim_io_lock;
 	kcondvar_t	vdev_trim_io_cv;
-	uint64_t	vdev_trim_inflight[2];
+	uint64_t	vdev_trim_inflight[3];
 
 	/*
 	 * Values stored in the config for an indirect or removing vdev.
diff --git a/include/sys/vdev_trim.h b/include/sys/vdev_trim.h
index 1e5401766..16f4be2a4 100644
--- a/include/sys/vdev_trim.h
+++ b/include/sys/vdev_trim.h
@@ -44,6 +44,8 @@ extern void vdev_autotrim(spa_t *spa);
 extern void vdev_autotrim_stop_all(spa_t *spa);
 extern void vdev_autotrim_stop_wait(vdev_t *vd);
 extern void vdev_autotrim_restart(spa_t *spa);
+extern int vdev_trim_simple(vdev_t *vd, uint64_t start, uint64_t size);
+extern void vdev_trim_l2arc(spa_t *spa);
 
 #ifdef	__cplusplus
 }