Finally drop long disabled vdev cache.

It was a vdev level read cache, designed to aggregate many small
reads by speculatively issuing bigger reads instead and caching
the result.  But since it has almost no idea about what is going
on with exception of ZIO_FLAG_DONT_CACHE flag set by higher layers,
it was found to make more harm than good, for which reason it was
disabled for the past 12 years.  These days we have much better
instruments to enlarge the I/Os, such as speculative and prescient
prefetches, I/O scheduler, I/O aggregation etc.

Besides just the dead code removal this removes one extra mutex
lock/unlock per write inside vdev_cache_write(), not otherwise
disabled and trying to do some work.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #14953

cmd/arc_summary

@@ -64,7 +64,6 @@ SECTION_HELP = 'print info from one section ('+' '.join(SECTIONS)+')'
 SECTION_PATHS = {'arc': 'arcstats',
                  'dmu': 'dmu_tx',
                  'l2arc': 'arcstats',  # L2ARC stuff lives in arcstats
-                 'vdev': 'vdev_cache_stats',
                  'zfetch': 'zfetchstats',
                  'zil': 'zil'}
 
@@ -90,8 +89,6 @@ if sys.platform.startswith('freebsd'):
     # Requires py36-sysctl on FreeBSD
     import sysctl
 
-    VDEV_CACHE_SIZE = 'vdev.cache_size'
-
     def is_value(ctl):
         return ctl.type != sysctl.CTLTYPE_NODE
 
@@ -135,8 +132,6 @@ elif sys.platform.startswith('linux'):
     SPL_PATH = '/sys/module/spl/parameters'
     TUNABLES_PATH = '/sys/module/zfs/parameters'
 
-    VDEV_CACHE_SIZE = 'zfs_vdev_cache_size'
-
     def load_kstats(section):
         path = os.path.join(KSTAT_PATH, section)
         with open(path) as f:
@@ -952,35 +947,6 @@ def section_tunables(*_):
     print()
 
 
-def section_vdev(kstats_dict):
-    """Collect information on VDEV caches"""
-
-    # Currently [Nov 2017] the VDEV cache is disabled, because it is actually
-    # harmful. When this is the case, we just skip the whole entry. See
-    # https://github.com/openzfs/zfs/blob/master/module/zfs/vdev_cache.c
-    # for details
-    tunables = get_vdev_params()
-
-    if tunables[VDEV_CACHE_SIZE] == '0':
-        print('VDEV cache disabled, skipping section\n')
-        return
-
-    vdev_stats = isolate_section('vdev_cache_stats', kstats_dict)
-
-    vdev_cache_total = int(vdev_stats['hits']) +\
-        int(vdev_stats['misses']) +\
-        int(vdev_stats['delegations'])
-
-    prt_1('VDEV cache summary:', f_hits(vdev_cache_total))
-    prt_i2('Hit ratio:', f_perc(vdev_stats['hits'], vdev_cache_total),
-           f_hits(vdev_stats['hits']))
-    prt_i2('Miss ratio:', f_perc(vdev_stats['misses'], vdev_cache_total),
-           f_hits(vdev_stats['misses']))
-    prt_i2('Delegations:', f_perc(vdev_stats['delegations'], vdev_cache_total),
-           f_hits(vdev_stats['delegations']))
-    print()
-
-
 def section_zil(kstats_dict):
     """Collect information on the ZFS Intent Log. Some of the information
     taken from https://github.com/openzfs/zfs/blob/master/include/sys/zil.h
@@ -1008,7 +974,6 @@ section_calls = {'arc': section_arc,
                  'l2arc': section_l2arc,
                  'spl': section_spl,
                  'tunables': section_tunables,
-                 'vdev': section_vdev,
                  'zil': section_zil}
 
 

cmd/zdb/zdb.c

@@ -8546,9 +8546,9 @@ zdb_read_block(char *thing, spa_t *spa)
 		 */
 		zio_nowait(zio_vdev_child_io(zio, bp, vd, offset, pabd,
 		    psize, ZIO_TYPE_READ, ZIO_PRIORITY_SYNC_READ,
-		    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_PROPAGATE |
-		    ZIO_FLAG_DONT_RETRY | ZIO_FLAG_CANFAIL | ZIO_FLAG_RAW |
-		    ZIO_FLAG_OPTIONAL, NULL, NULL));
+		    ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY |
+		    ZIO_FLAG_CANFAIL | ZIO_FLAG_RAW | ZIO_FLAG_OPTIONAL,
+		    NULL, NULL));
 	}
 
 	error = zio_wait(zio);
@@ -8642,7 +8642,6 @@ zdb_read_block(char *thing, spa_t *spa)
 				zio_nowait(zio_vdev_child_io(czio, bp, vd,
 				    offset, pabd, psize, ZIO_TYPE_READ,
 				    ZIO_PRIORITY_SYNC_READ,
-				    ZIO_FLAG_DONT_CACHE |
 				    ZIO_FLAG_DONT_PROPAGATE |
 				    ZIO_FLAG_DONT_RETRY |
 				    ZIO_FLAG_CANFAIL | ZIO_FLAG_RAW |

include/os/linux/kernel/linux/mod_compat.h

@@ -68,7 +68,6 @@ enum scope_prefix_types {
 	zfs_trim,
 	zfs_txg,
 	zfs_vdev,
-	zfs_vdev_cache,
 	zfs_vdev_file,
 	zfs_vdev_mirror,
 	zfs_vnops,

include/sys/spa.h

@@ -1174,10 +1174,6 @@ extern void zep_to_zb(uint64_t dataset, zbookmark_err_phys_t *zep,
     zbookmark_phys_t *zb);
 extern void name_to_errphys(char *buf, zbookmark_err_phys_t *zep);
 
-/* vdev cache */
-extern void vdev_cache_stat_init(void);
-extern void vdev_cache_stat_fini(void);
-
 /* vdev mirror */
 extern void vdev_mirror_stat_init(void);
 extern void vdev_mirror_stat_fini(void);

include/sys/vdev.h

@@ -158,12 +158,6 @@ extern boolean_t vdev_allocatable(vdev_t *vd);
 extern boolean_t vdev_accessible(vdev_t *vd, zio_t *zio);
 extern boolean_t vdev_is_spacemap_addressable(vdev_t *vd);
 
-extern void vdev_cache_init(vdev_t *vd);
-extern void vdev_cache_fini(vdev_t *vd);
-extern boolean_t vdev_cache_read(zio_t *zio);
-extern void vdev_cache_write(zio_t *zio);
-extern void vdev_cache_purge(vdev_t *vd);
-
 extern void vdev_queue_init(vdev_t *vd);
 extern void vdev_queue_fini(vdev_t *vd);
 extern zio_t *vdev_queue_io(zio_t *zio);

include/sys/vdev_impl.h

@@ -57,8 +57,6 @@ extern "C" {
  * Forward declarations that lots of things need.
  */
 typedef struct vdev_queue vdev_queue_t;
-typedef struct vdev_cache vdev_cache_t;
-typedef struct vdev_cache_entry vdev_cache_entry_t;
 struct abd;
 
 extern uint_t zfs_vdev_queue_depth_pct;
@@ -132,23 +130,6 @@ typedef const struct vdev_ops {
 /*
  * Virtual device properties
  */
-struct vdev_cache_entry {
-	struct abd	*ve_abd;
-	uint64_t	ve_offset;
-	clock_t		ve_lastused;
-	avl_node_t	ve_offset_node;
-	avl_node_t	ve_lastused_node;
-	uint32_t	ve_hits;
-	uint16_t	ve_missed_update;
-	zio_t		*ve_fill_io;
-};
-
-struct vdev_cache {
-	avl_tree_t	vc_offset_tree;
-	avl_tree_t	vc_lastused_tree;
-	kmutex_t	vc_lock;
-};
-
 typedef struct vdev_queue_class {
 	uint32_t	vqc_active;
 
@@ -443,7 +424,6 @@ struct vdev {
 	boolean_t	vdev_resilver_deferred;  /* resilver deferred */
 	boolean_t	vdev_kobj_flag; /* kobj event record */
 	vdev_queue_t	vdev_queue;	/* I/O deadline schedule queue	*/
-	vdev_cache_t	vdev_cache;	/* physical block cache		*/
 	spa_aux_vdev_t	*vdev_aux;	/* for l2cache and spares vdevs	*/
 	zio_t		*vdev_probe_zio; /* root of current probe	*/
 	vdev_aux_t	vdev_label_aux;	/* on-disk aux state		*/

include/sys/zio.h

@@ -190,7 +190,6 @@ typedef uint64_t zio_flag_t;
 #define	ZIO_FLAG_SPECULATIVE	(1ULL << 8)
 #define	ZIO_FLAG_CONFIG_WRITER	(1ULL << 9)
 #define	ZIO_FLAG_DONT_RETRY	(1ULL << 10)
-#define	ZIO_FLAG_DONT_CACHE	(1ULL << 11)
 #define	ZIO_FLAG_NODATA		(1ULL << 12)
 #define	ZIO_FLAG_INDUCE_DAMAGE	(1ULL << 13)
 #define	ZIO_FLAG_IO_ALLOCATING	(1ULL << 14)

lib/libzpool/Makefile.am

@@ -135,7 +135,6 @@ nodist_libzpool_la_SOURCES = \
 	module/zfs/uberblock.c \
 	module/zfs/unique.c \
 	module/zfs/vdev.c \
-	module/zfs/vdev_cache.c \
 	module/zfs/vdev_draid.c \
 	module/zfs/vdev_draid_rand.c \
 	module/zfs/vdev_indirect.c \

man/man4/zfs.4

@@ -2028,21 +2028,6 @@ Max vdev I/O aggregation size.
 .It Sy zfs_vdev_aggregation_limit_non_rotating Ns = Ns Sy 131072 Ns B Po 128 KiB Pc Pq uint
 Max vdev I/O aggregation size for non-rotating media.
 .
-.It Sy zfs_vdev_cache_bshift Ns = Ns Sy 16 Po 64 KiB Pc Pq uint
-Shift size to inflate reads to.
-.
-.It Sy zfs_vdev_cache_max Ns = Ns Sy 16384 Ns B Po 16 KiB Pc Pq uint
-Inflate reads smaller than this value to meet the
-.Sy zfs_vdev_cache_bshift
-size
-.Pq default Sy 64 KiB .
-.
-.It Sy zfs_vdev_cache_size Ns = Ns Sy 0 Pq uint
-Total size of the per-disk cache in bytes.
-.Pp
-Currently this feature is disabled, as it has been found to not be helpful
-for performance and in some cases harmful.
-.
 .It Sy zfs_vdev_mirror_rotating_inc Ns = Ns Sy 0 Pq int
 A number by which the balancing algorithm increments the load calculation for
 the purpose of selecting the least busy mirror member when an I/O operation

man/man8/zpool-events.8

@@ -456,7 +456,6 @@ ZIO_FLAG_CANFAIL:0x00000080
 ZIO_FLAG_SPECULATIVE:0x00000100
 ZIO_FLAG_CONFIG_WRITER:0x00000200
 ZIO_FLAG_DONT_RETRY:0x00000400
-ZIO_FLAG_DONT_CACHE:0x00000800
 ZIO_FLAG_NODATA:0x00001000
 ZIO_FLAG_INDUCE_DAMAGE:0x00002000
 

module/Kbuild.in

@@ -382,7 +382,6 @@ ZFS_OBJS := \
 	uberblock.o \
 	unique.o \
 	vdev.o \
-	vdev_cache.o \
 	vdev_draid.o \
 	vdev_draid_rand.o \
 	vdev_indirect.o \

module/Makefile.bsd

@@ -308,7 +308,6 @@ SRCS+=	abd.c \
 	uberblock.c \
 	unique.c \
 	vdev.c \
-	vdev_cache.c \
 	vdev_draid.c \
 	vdev_draid_rand.c \
 	vdev_indirect.c \

module/os/freebsd/zfs/sysctl_os.c

@@ -872,8 +872,6 @@ SYSCTL_INT(_vfs_zfs, OID_AUTO, validate_skip,
 	"Enable to bypass vdev_validate().");
 /* END CSTYLED */
 
-/* vdev_cache.c */
-
 /* vdev_mirror.c */
 
 /* vdev_queue.c */

module/zfs/arc.c

@@ -6106,8 +6106,7 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
 				    asize, abd,
 				    ZIO_CHECKSUM_OFF,
 				    l2arc_read_done, cb, priority,
-				    zio_flags | ZIO_FLAG_DONT_CACHE |
-				    ZIO_FLAG_CANFAIL |
+				    zio_flags | ZIO_FLAG_CANFAIL |
 				    ZIO_FLAG_DONT_PROPAGATE |
 				    ZIO_FLAG_DONT_RETRY, B_FALSE);
 				acb->acb_zio_head = rzio;
@@ -10177,8 +10176,7 @@ l2arc_dev_hdr_read(l2arc_dev_t *dev)
 	err = zio_wait(zio_read_phys(NULL, dev->l2ad_vdev,
 	    VDEV_LABEL_START_SIZE, l2dhdr_asize, abd,
 	    ZIO_CHECKSUM_LABEL, NULL, NULL, ZIO_PRIORITY_SYNC_READ,
-	    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_CANFAIL |
-	    ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY |
+	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY |
 	    ZIO_FLAG_SPECULATIVE, B_FALSE));
 
 	abd_free(abd);
@@ -10498,11 +10496,10 @@ l2arc_log_blk_fetch(vdev_t *vd, const l2arc_log_blkptr_t *lbp,
 	cb = kmem_zalloc(sizeof (l2arc_read_callback_t), KM_SLEEP);
 	cb->l2rcb_abd = abd_get_from_buf(lb, asize);
 	pio = zio_root(vd->vdev_spa, l2arc_blk_fetch_done, cb,
-	    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE |
-	    ZIO_FLAG_DONT_RETRY);
+	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY);
 	(void) zio_nowait(zio_read_phys(pio, vd, lbp->lbp_daddr, asize,
 	    cb->l2rcb_abd, ZIO_CHECKSUM_OFF, NULL, NULL,
-	    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_DONT_CACHE | ZIO_FLAG_CANFAIL |
+	    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL |
 	    ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY, B_FALSE));
 
 	return (pio);

module/zfs/dmu_recv.c

@@ -1371,8 +1371,8 @@ do_corrective_recv(struct receive_writer_arg *rwa, struct drr_write *drrw,
 	dnode_t *dn;
 	abd_t *abd = rrd->abd;
 	zio_cksum_t bp_cksum = bp->blk_cksum;
-	zio_flag_t flags = ZIO_FLAG_SPECULATIVE |
-	    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_RETRY | ZIO_FLAG_CANFAIL;
+	zio_flag_t flags = ZIO_FLAG_SPECULATIVE | ZIO_FLAG_DONT_RETRY |
+	    ZIO_FLAG_CANFAIL;
 
 	if (rwa->raw)
 		flags |= ZIO_FLAG_RAW;

module/zfs/spa_misc.c

@@ -2438,7 +2438,6 @@ spa_init(spa_mode_t mode)
 	zio_init();
 	dmu_init();
 	zil_init();
-	vdev_cache_stat_init();
 	vdev_mirror_stat_init();
 	vdev_raidz_math_init();
 	vdev_file_init();
@@ -2462,7 +2461,6 @@ spa_fini(void)
 	spa_evict_all();
 
 	vdev_file_fini();
-	vdev_cache_stat_fini();
 	vdev_mirror_stat_fini();
 	vdev_raidz_math_fini();
 	chksum_fini();

module/zfs/vdev.c

@@ -715,7 +715,6 @@ vdev_alloc_common(spa_t *spa, uint_t id, uint64_t guid, vdev_ops_t *ops)
 	    offsetof(struct vdev, vdev_dtl_node));
 	vd->vdev_stat.vs_timestamp = gethrtime();
 	vdev_queue_init(vd);
-	vdev_cache_init(vd);
 
 	return (vd);
 }
@@ -1096,7 +1095,6 @@ vdev_free(vdev_t *vd)
 	 * Clean up vdev structure.
 	 */
 	vdev_queue_fini(vd);
-	vdev_cache_fini(vd);
 
 	if (vd->vdev_path)
 		spa_strfree(vd->vdev_path);
@@ -1720,8 +1718,7 @@ vdev_probe(vdev_t *vd, zio_t *zio)
 		vps = kmem_zalloc(sizeof (*vps), KM_SLEEP);
 
 		vps->vps_flags = ZIO_FLAG_CANFAIL | ZIO_FLAG_PROBE |
-		    ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_AGGREGATE |
-		    ZIO_FLAG_TRYHARD;
+		    ZIO_FLAG_DONT_AGGREGATE | ZIO_FLAG_TRYHARD;
 
 		if (spa_config_held(spa, SCL_ZIO, RW_WRITER)) {
 			/*
@@ -2612,8 +2609,6 @@ vdev_close(vdev_t *vd)
 
 	vd->vdev_ops->vdev_op_close(vd);
 
-	vdev_cache_purge(vd);
-
 	/*
 	 * We record the previous state before we close it, so that if we are
 	 * doing a reopen(), we don't generate FMA ereports if we notice that