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mirror_zfs/include/sys/vdev.h
Paul Dagnelie ca5777793e Reduce loaded range tree memory usage 
This patch implements a new tree structure for ZFS, and uses it to 
store range trees more efficiently.

The new structure is approximately a B-tree, though there are some 
small differences from the usual characterizations. The tree has core 
nodes and leaf nodes; each contain data elements, which the elements 
in the core nodes acting as separators between its children. The 
difference between core and leaf nodes is that the core nodes have an 
array of children, while leaf nodes don't. Every node in the tree may 
be only partially full; in most cases, they are all at least 50% full 
(in terms of element count) except for the root node, which can be 
less full. Underfull nodes will steal from their neighbors or merge to 
remain full enough, while overfull nodes will split in two. The data 
elements are contained in tree-controlled buffers; they are copied 
into these on insertion, and overwritten on deletion. This means that 
the elements are not independently allocated, which reduces overhead, 
but also means they can't be shared between trees (and also that 
pointers to them are only valid until a side-effectful tree operation 
occurs). The overhead varies based on how dense the tree is, but is 
usually on the order of about 50% of the element size; the per-node 
overheads are very small, and so don't make a significant difference. 
The trees can accept arbitrary records; they accept a size and a 
comparator to allow them to be used for a variety of purposes.

The new trees replace the AVL trees used in the range trees today. 
Currently, the range_seg_t structure contains three 8 byte integers 
of payload and two 24 byte avl_tree_node_ts to handle its storage in 
both an offset-sorted tree and a size-sorted tree (total size: 64 
bytes). In the new model, the range seg structures are usually two 4 
byte integers, but a separate one needs to exist for the size-sorted 
and offset-sorted tree. Between the raw size, the 50% overhead, and 
the double storage, the new btrees are expected to use 8*1.5*2 = 24 
bytes per record, or 33.3% as much memory as the AVL trees (this is 
for the purposes of storing metaslab range trees; for other purposes, 
like scrubs, they use ~50% as much memory).

We reduced the size of the payload in the range segments by teaching 
range trees about starting offsets and shifts; since metaslabs have a 
fixed starting offset, and they all operate in terms of disk sectors, 
we can store the ranges using 4-byte integers as long as the size of 
the metaslab divided by the sector size is less than 2^32. For 512-byte
sectors, this is a 2^41 (or 2TB) metaslab, which with the default
settings corresponds to a 256PB disk. 4k sector disks can handle 
metaslabs up to 2^46 bytes, or 2^63 byte disks. Since we do not 
anticipate disks of this size in the near future, there should be 
almost no cases where metaslabs need 64-byte integers to store their 
ranges. We do still have the capability to store 64-byte integer ranges 
to account for cases where we are storing per-vdev (or per-dnode) trees, 
which could reasonably go above the limits discussed. We also do not 
store fill information in the compact version of the node, since it 
is only used for sorted scrub.

We also optimized the metaslab loading process in various other ways
to offset some inefficiencies in the btree model. While individual
operations (find, insert, remove_from) are faster for the btree than 
they are for the avl tree, remove usually requires a find operation, 
while in the AVL tree model the element itself suffices. Some clever 
changes actually caused an overall speedup in metaslab loading; we use 
approximately 40% less cpu to load metaslabs in our tests on Illumos.

Another memory and performance optimization was achieved by changing 
what is stored in the size-sorted trees. When a disk is heavily 
fragmented, the df algorithm used by default in ZFS will almost always 
find a number of small regions in its initial cursor-based search; it 
will usually only fall back to the size-sorted tree to find larger 
regions. If we increase the size of the cursor-based search slightly, 
and don't store segments that are smaller than a tunable size floor 
in the size-sorted tree, we can further cut memory usage down to 
below 20% of what the AVL trees store. This also results in further 
reductions in CPU time spent loading metaslabs.

The 16KiB size floor was chosen because it results in substantial memory 
usage reduction while not usually resulting in situations where we can't 
find an appropriate chunk with the cursor and are forced to use an 
oversized chunk from the size-sorted tree. In addition, even if we do 
have to use an oversized chunk from the size-sorted tree, the chunk 
would be too small to use for ZIL allocations, so it isn't as big of a 
loss as it might otherwise be. And often, more small allocations will 
follow the initial one, and the cursor search will now find the 
remainder of the chunk we didn't use all of and use it for subsequent 
allocations. Practical testing has shown little or no change in 
fragmentation as a result of this change.

If the size-sorted tree becomes empty while the offset sorted one still 
has entries, it will load all the entries from the offset sorted tree 
and disregard the size floor until it is unloaded again. This operation 
occurs rarely with the default setting, only on incredibly thoroughly 
fragmented pools.

There are some other small changes to zdb to teach it to handle btrees, 
but nothing major.
                                           
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed by: Sebastien Roy seb@delphix.com
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #9181
2019-10-09 10:36:03 -07:00

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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2011, 2017 by Delphix. All rights reserved.
* Copyright (c) 2017, Intel Corporation.
*/
#ifndef _SYS_VDEV_H
#define _SYS_VDEV_H
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu.h>
#include <sys/space_map.h>
#include <sys/fs/zfs.h>
#ifdef __cplusplus
extern "C" {
#endif
typedef enum vdev_dtl_type {
DTL_MISSING, /* 0% replication: no copies of the data */
DTL_PARTIAL, /* less than 100% replication: some copies missing */
DTL_SCRUB, /* unable to fully repair during scrub/resilver */
DTL_OUTAGE, /* temporarily missing (used to attempt detach) */
DTL_TYPES
} vdev_dtl_type_t;
extern int zfs_nocacheflush;
extern void vdev_dbgmsg(vdev_t *vd, const char *fmt, ...);
extern void vdev_dbgmsg_print_tree(vdev_t *, int);
extern int vdev_open(vdev_t *);
extern void vdev_open_children(vdev_t *);
extern int vdev_validate(vdev_t *);
extern int vdev_copy_path_strict(vdev_t *, vdev_t *);
extern void vdev_copy_path_relaxed(vdev_t *, vdev_t *);
extern void vdev_close(vdev_t *);
extern int vdev_create(vdev_t *, uint64_t txg, boolean_t isreplace);
extern void vdev_reopen(vdev_t *);
extern int vdev_validate_aux(vdev_t *vd);
extern zio_t *vdev_probe(vdev_t *vd, zio_t *pio);
extern boolean_t vdev_is_concrete(vdev_t *vd);
extern boolean_t vdev_is_bootable(vdev_t *vd);
extern vdev_t *vdev_lookup_top(spa_t *spa, uint64_t vdev);
extern vdev_t *vdev_lookup_by_guid(vdev_t *vd, uint64_t guid);
extern int vdev_count_leaves(spa_t *spa);
extern void vdev_dtl_dirty(vdev_t *vd, vdev_dtl_type_t d,
uint64_t txg, uint64_t size);
extern boolean_t vdev_dtl_contains(vdev_t *vd, vdev_dtl_type_t d,
uint64_t txg, uint64_t size);
extern boolean_t vdev_dtl_empty(vdev_t *vd, vdev_dtl_type_t d);
extern boolean_t vdev_dtl_need_resilver(vdev_t *vd, uint64_t off, size_t size);
extern void vdev_dtl_reassess(vdev_t *vd, uint64_t txg, uint64_t scrub_txg,
int scrub_done);
extern boolean_t vdev_dtl_required(vdev_t *vd);
extern boolean_t vdev_resilver_needed(vdev_t *vd,
uint64_t *minp, uint64_t *maxp);
extern void vdev_destroy_unlink_zap(vdev_t *vd, uint64_t zapobj,
dmu_tx_t *tx);
extern uint64_t vdev_create_link_zap(vdev_t *vd, dmu_tx_t *tx);
extern void vdev_construct_zaps(vdev_t *vd, dmu_tx_t *tx);
extern void vdev_destroy_spacemaps(vdev_t *vd, dmu_tx_t *tx);
extern void vdev_indirect_mark_obsolete(vdev_t *vd, uint64_t offset,
uint64_t size);
extern void spa_vdev_indirect_mark_obsolete(spa_t *spa, uint64_t vdev,
uint64_t offset, uint64_t size, dmu_tx_t *tx);
extern boolean_t vdev_replace_in_progress(vdev_t *vdev);
extern void vdev_hold(vdev_t *);
extern void vdev_rele(vdev_t *);
extern int vdev_metaslab_init(vdev_t *vd, uint64_t txg);
extern void vdev_metaslab_fini(vdev_t *vd);
extern void vdev_metaslab_set_size(vdev_t *);
extern void vdev_expand(vdev_t *vd, uint64_t txg);
extern void vdev_split(vdev_t *vd);
extern void vdev_deadman(vdev_t *vd, char *tag);
extern void vdev_xlate(vdev_t *vd, const range_seg64_t *logical_rs,
range_seg64_t *physical_rs);
extern void vdev_get_stats_ex(vdev_t *vd, vdev_stat_t *vs, vdev_stat_ex_t *vsx);
extern void vdev_get_stats(vdev_t *vd, vdev_stat_t *vs);
extern void vdev_clear_stats(vdev_t *vd);
extern void vdev_stat_update(zio_t *zio, uint64_t psize);
extern void vdev_scan_stat_init(vdev_t *vd);
extern void vdev_propagate_state(vdev_t *vd);
extern void vdev_set_state(vdev_t *vd, boolean_t isopen, vdev_state_t state,
vdev_aux_t aux);
extern boolean_t vdev_children_are_offline(vdev_t *vd);
extern void vdev_space_update(vdev_t *vd,
int64_t alloc_delta, int64_t defer_delta, int64_t space_delta);
extern int64_t vdev_deflated_space(vdev_t *vd, int64_t space);
extern uint64_t vdev_psize_to_asize(vdev_t *vd, uint64_t psize);
extern int vdev_fault(spa_t *spa, uint64_t guid, vdev_aux_t aux);
extern int vdev_degrade(spa_t *spa, uint64_t guid, vdev_aux_t aux);
extern int vdev_online(spa_t *spa, uint64_t guid, uint64_t flags,
vdev_state_t *);
extern int vdev_offline(spa_t *spa, uint64_t guid, uint64_t flags);
extern void vdev_clear(spa_t *spa, vdev_t *vd);
extern boolean_t vdev_is_dead(vdev_t *vd);
extern boolean_t vdev_readable(vdev_t *vd);
extern boolean_t vdev_writeable(vdev_t *vd);
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);
extern void vdev_queue_io_done(zio_t *zio);
extern void vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority);
extern int vdev_queue_length(vdev_t *vd);
extern uint64_t vdev_queue_last_offset(vdev_t *vd);
extern void vdev_config_dirty(vdev_t *vd);
extern void vdev_config_clean(vdev_t *vd);
extern int vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg);
extern void vdev_state_dirty(vdev_t *vd);
extern void vdev_state_clean(vdev_t *vd);
extern void vdev_set_deferred_resilver(spa_t *spa, vdev_t *vd);
typedef enum vdev_config_flag {
VDEV_CONFIG_SPARE = 1 << 0,
VDEV_CONFIG_L2CACHE = 1 << 1,
VDEV_CONFIG_REMOVING = 1 << 2,
VDEV_CONFIG_MOS = 1 << 3,
VDEV_CONFIG_MISSING = 1 << 4
} vdev_config_flag_t;
extern void vdev_top_config_generate(spa_t *spa, nvlist_t *config);
extern nvlist_t *vdev_config_generate(spa_t *spa, vdev_t *vd,
boolean_t getstats, vdev_config_flag_t flags);
/*
* Label routines
*/
struct uberblock;
extern uint64_t vdev_label_offset(uint64_t psize, int l, uint64_t offset);
extern int vdev_label_number(uint64_t psise, uint64_t offset);
extern nvlist_t *vdev_label_read_config(vdev_t *vd, uint64_t txg);
extern void vdev_uberblock_load(vdev_t *, struct uberblock *, nvlist_t **);
extern void vdev_config_generate_stats(vdev_t *vd, nvlist_t *nv);
extern void vdev_label_write(zio_t *zio, vdev_t *vd, int l, abd_t *buf, uint64_t
offset, uint64_t size, zio_done_func_t *done, void *private, int flags);
typedef enum {
VDEV_LABEL_CREATE, /* create/add a new device */
VDEV_LABEL_REPLACE, /* replace an existing device */
VDEV_LABEL_SPARE, /* add a new hot spare */
VDEV_LABEL_REMOVE, /* remove an existing device */
VDEV_LABEL_L2CACHE, /* add an L2ARC cache device */
VDEV_LABEL_SPLIT /* generating new label for split-off dev */
} vdev_labeltype_t;
extern int vdev_label_init(vdev_t *vd, uint64_t txg, vdev_labeltype_t reason);
#ifdef __cplusplus
}
#endif
#endif /* _SYS_VDEV_H */
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