include/sys/metaslab_impl.h

   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 /*
  27  * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
  28  */
  29
  30 #ifndef _SYS_METASLAB_IMPL_H
  31 #define _SYS_METASLAB_IMPL_H
  32
  33 #include <sys/metaslab.h>
  34 #include <sys/space_map.h>
  35 #include <sys/range_tree.h>
  36 #include <sys/vdev.h>
  37 #include <sys/txg.h>
  38 #include <sys/avl.h>
  39
  40 #ifdef  __cplusplus
  41 extern "C" {
  42 #endif
  43
  44 /*
  45  * A metaslab class encompasses a category of allocatable top-level vdevs.
  46  * Each top-level vdev is associated with a metaslab group which defines
  47  * the allocatable region for that vdev. Examples of these categories include
  48  * "normal" for data block allocations (i.e. main pool allocations) or "log"
  49  * for allocations designated for intent log devices (i.e. slog devices).
  50  * When a block allocation is requested from the SPA it is associated with a
  51  * metaslab_class_t, and only top-level vdevs (i.e. metaslab groups) belonging
  52  * to the class can be used to satisfy that request. Allocations are done
  53  * by traversing the metaslab groups that are linked off of the mc_rotor field.
  54  * This rotor points to the next metaslab group where allocations will be
  55  * attempted. Allocating a block is a 3 step process -- select the metaslab
  56  * group, select the metaslab, and then allocate the block. The metaslab
  57  * class defines the low-level block allocator that will be used as the
  58  * final step in allocation. These allocators are pluggable allowing each class
  59  * to use a block allocator that best suits that class.
  60  */
  61 struct metaslab_class {
  62         spa_t                   *mc_spa;
  63         metaslab_group_t        *mc_rotor;
  64         metaslab_ops_t          *mc_ops;
  65         uint64_t                mc_aliquot;
  66         uint64_t                mc_alloc_groups; /* # of allocatable groups */
  67         uint64_t                mc_alloc;       /* total allocated space */
  68         uint64_t                mc_deferred;    /* total deferred frees */
  69         uint64_t                mc_space;       /* total space (alloc + free) */
  70         uint64_t                mc_dspace;      /* total deflated space */
  71         uint64_t                mc_histogram[RANGE_TREE_HISTOGRAM_SIZE];
  72 };
  73
  74 /*
  75  * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
  76  * of a top-level vdev. They are linked togther to form a circular linked
  77  * list and can belong to only one metaslab class. Metaslab groups may become
  78  * ineligible for allocations for a number of reasons such as limited free
  79  * space, fragmentation, or going offline. When this happens the allocator will
  80  * simply find the next metaslab group in the linked list and attempt
  81  * to allocate from that group instead.
  82  */
  83 struct metaslab_group {
  84         kmutex_t                mg_lock;
  85         avl_tree_t              mg_metaslab_tree;
  86         uint64_t                mg_aliquot;
  87         boolean_t               mg_allocatable;         /* can we allocate? */
  88         uint64_t                mg_free_capacity;       /* percentage free */
  89         int64_t                 mg_bias;
  90         int64_t                 mg_activation_count;
  91         metaslab_class_t        *mg_class;
  92         vdev_t                  *mg_vd;
  93         taskq_t                 *mg_taskq;
  94         metaslab_group_t        *mg_prev;
  95         metaslab_group_t        *mg_next;
  96         uint64_t                mg_fragmentation;
  97         uint64_t                mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
  98 };
  99
 100 /*
 101  * This value defines the number of elements in the ms_lbas array. The value
 102  * of 64 was chosen as it covers all power of 2 buckets up to UINT64_MAX.
 103  * This is the equivalent of highbit(UINT64_MAX).
 104  */
 105 #define MAX_LBAS        64
 106
 107 /*
 108  * Each metaslab maintains a set of in-core trees to track metaslab operations.
 109  * The in-core free tree (ms_tree) contains the current list of free segments.
 110  * As blocks are allocated, the allocated segment are removed from the ms_tree
 111  * and added to a per txg allocation tree (ms_alloctree). As blocks are freed,
 112  * they are added to the per txg free tree (ms_freetree). These per txg
 113  * trees allow us to process all allocations and frees in syncing context
 114  * where it is safe to update the on-disk space maps. One additional in-core
 115  * tree is maintained to track deferred frees (ms_defertree). Once a block
 116  * is freed it will move from the ms_freetree to the ms_defertree. A deferred
 117  * free means that a block has been freed but cannot be used by the pool
 118  * until TXG_DEFER_SIZE transactions groups later. For example, a block
 119  * that is freed in txg 50 will not be available for reallocation until
 120  * txg 52 (50 + TXG_DEFER_SIZE).  This provides a safety net for uberblock
 121  * rollback. A pool could be safely rolled back TXG_DEFERS_SIZE
 122  * transactions groups and ensure that no block has been reallocated.
 123  *
 124  * The simplified transition diagram looks like this:
 125  *
 126  *
 127  *      ALLOCATE
 128  *         |
 129  *         V
 130  *    free segment (ms_tree) --------> ms_alloctree ----> (write to space map)
 131  *         ^
 132  *         |
 133  *         |                           ms_freetree <--- FREE
 134  *         |                                 |
 135  *         |                                 |
 136  *         |                                 |
 137  *         +----------- ms_defertree <-------+---------> (write to space map)
 138  *
 139  *
 140  * Each metaslab's space is tracked in a single space map in the MOS,
 141  * which is only updated in syncing context. Each time we sync a txg,
 142  * we append the allocs and frees from that txg to the space map.
 143  * The pool space is only updated once all metaslabs have finished syncing.
 144  *
 145  * To load the in-core free tree we read the space map from disk.
 146  * This object contains a series of alloc and free records that are
 147  * combined to make up the list of all free segments in this metaslab. These
 148  * segments are represented in-core by the ms_tree and are stored in an
 149  * AVL tree.
 150  *
 151  * As the space map grows (as a result of the appends) it will
 152  * eventually become space-inefficient. When the metaslab's in-core free tree
 153  * is zfs_condense_pct/100 times the size of the minimal on-disk
 154  * representation, we rewrite it in its minimized form. If a metaslab
 155  * needs to condense then we must set the ms_condensing flag to ensure
 156  * that allocations are not performed on the metaslab that is being written.
 157  */
 158 struct metaslab {
 159         kmutex_t        ms_lock;
 160         kcondvar_t      ms_load_cv;
 161         space_map_t     *ms_sm;
 162         metaslab_ops_t  *ms_ops;
 163         uint64_t        ms_id;
 164         uint64_t        ms_start;
 165         uint64_t        ms_size;
 166         uint64_t        ms_fragmentation;
 167
 168         range_tree_t    *ms_alloctree[TXG_SIZE];
 169         range_tree_t    *ms_freetree[TXG_SIZE];
 170         range_tree_t    *ms_defertree[TXG_DEFER_SIZE];
 171         range_tree_t    *ms_tree;
 172
 173         boolean_t       ms_condensing;  /* condensing? */
 174         boolean_t       ms_condense_wanted;
 175         boolean_t       ms_loaded;
 176         boolean_t       ms_loading;
 177
 178         int64_t         ms_deferspace;  /* sum of ms_defermap[] space   */
 179         uint64_t        ms_weight;      /* weight vs. others in group   */
 180         uint64_t        ms_access_txg;
 181
 182         /*
 183          * The metaslab block allocators can optionally use a size-ordered
 184          * range tree and/or an array of LBAs. Not all allocators use
 185          * this functionality. The ms_size_tree should always contain the
 186          * same number of segments as the ms_tree. The only difference
 187          * is that the ms_size_tree is ordered by segment sizes.
 188          */
 189         avl_tree_t      ms_size_tree;
 190         uint64_t        ms_lbas[MAX_LBAS];
 191
 192         metaslab_group_t *ms_group;     /* metaslab group               */
 193         avl_node_t      ms_group_node;  /* node in metaslab group tree  */
 194         txg_node_t      ms_txg_node;    /* per-txg dirty metaslab links */
 195 };
 196
 197 #ifdef  __cplusplus
 198 }
 199 #endif
 200
 201 #endif  /* _SYS_METASLAB_IMPL_H */