space_reftree.c revision 290765 
1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21/*
22 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
23 * Use is subject to license terms.
24 */
25/*
26 * Copyright (c) 2013, 2015 by Delphix. All rights reserved.
27 */
28
29#include <sys/zfs_context.h>
30#include <sys/range_tree.h>
31#include <sys/space_reftree.h>
32
33/*
34 * Space reference trees.
35 *
36 * A range tree is a collection of integers.  Every integer is either
37 * in the tree, or it's not.  A space reference tree generalizes
38 * the idea: it allows its members to have arbitrary reference counts,
39 * as opposed to the implicit reference count of 0 or 1 in a range tree.
40 * This representation comes in handy when computing the union or
41 * intersection of multiple space maps.  For example, the union of
42 * N range trees is the subset of the reference tree with refcnt >= 1.
43 * The intersection of N range trees is the subset with refcnt >= N.
44 *
45 * [It's very much like a Fourier transform.  Unions and intersections
46 * are hard to perform in the 'range tree domain', so we convert the trees
47 * into the 'reference count domain', where it's trivial, then invert.]
48 *
49 * vdev_dtl_reassess() uses computations of this form to determine
50 * DTL_MISSING and DTL_OUTAGE for interior vdevs -- e.g. a RAID-Z vdev
51 * has an outage wherever refcnt >= vdev_nparity + 1, and a mirror vdev
52 * has an outage wherever refcnt >= vdev_children.
53 */
54static int
55space_reftree_compare(const void *x1, const void *x2)
56{
57	const space_ref_t *sr1 = x1;
58	const space_ref_t *sr2 = x2;
59
60	if (sr1->sr_offset < sr2->sr_offset)
61		return (-1);
62	if (sr1->sr_offset > sr2->sr_offset)
63		return (1);
64
65	if (sr1 < sr2)
66		return (-1);
67	if (sr1 > sr2)
68		return (1);
69
70	return (0);
71}
72
73void
74space_reftree_create(avl_tree_t *t)
75{
76	avl_create(t, space_reftree_compare,
77	    sizeof (space_ref_t), offsetof(space_ref_t, sr_node));
78}
79
80void
81space_reftree_destroy(avl_tree_t *t)
82{
83	space_ref_t *sr;
84	void *cookie = NULL;
85
86	while ((sr = avl_destroy_nodes(t, &cookie)) != NULL)
87		kmem_free(sr, sizeof (*sr));
88
89	avl_destroy(t);
90}
91
92static void
93space_reftree_add_node(avl_tree_t *t, uint64_t offset, int64_t refcnt)
94{
95	space_ref_t *sr;
96
97	sr = kmem_alloc(sizeof (*sr), KM_SLEEP);
98	sr->sr_offset = offset;
99	sr->sr_refcnt = refcnt;
100
101	avl_add(t, sr);
102}
103
104void
105space_reftree_add_seg(avl_tree_t *t, uint64_t start, uint64_t end,
106    int64_t refcnt)
107{
108	space_reftree_add_node(t, start, refcnt);
109	space_reftree_add_node(t, end, -refcnt);
110}
111
112/*
113 * Convert (or add) a range tree into a reference tree.
114 */
115void
116space_reftree_add_map(avl_tree_t *t, range_tree_t *rt, int64_t refcnt)
117{
118	range_seg_t *rs;
119
120	ASSERT(MUTEX_HELD(rt->rt_lock));
121
122	for (rs = avl_first(&rt->rt_root); rs; rs = AVL_NEXT(&rt->rt_root, rs))
123		space_reftree_add_seg(t, rs->rs_start, rs->rs_end, refcnt);
124}
125
126/*
127 * Convert a reference tree into a range tree.  The range tree will contain
128 * all members of the reference tree for which refcnt >= minref.
129 */
130void
131space_reftree_generate_map(avl_tree_t *t, range_tree_t *rt, int64_t minref)
132{
133	uint64_t start = -1ULL;
134	int64_t refcnt = 0;
135	space_ref_t *sr;
136
137	ASSERT(MUTEX_HELD(rt->rt_lock));
138
139	range_tree_vacate(rt, NULL, NULL);
140
141	for (sr = avl_first(t); sr != NULL; sr = AVL_NEXT(t, sr)) {
142		refcnt += sr->sr_refcnt;
143		if (refcnt >= minref) {
144			if (start == -1ULL) {
145				start = sr->sr_offset;
146			}
147		} else {
148			if (start != -1ULL) {
149				uint64_t end = sr->sr_offset;
150				ASSERT(start <= end);
151				if (end > start)
152					range_tree_add(rt, start, end - start);
153				start = -1ULL;
154			}
155		}
156	}
157	ASSERT(refcnt == 0);
158	ASSERT(start == -1ULL);
159}
160