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30 #ifndef _SYS_METASLAB_IMPL_H
31 #define _SYS_METASLAB_IMPL_H
33 #include <sys/metaslab.h>
34 #include <sys/space_map.h>
35 #include <sys/range_tree.h>
45 * Metaslab allocation tracing record.
47 typedef struct metaslab_alloc_trace {
48 list_node_t mat_list_node;
49 metaslab_group_t *mat_mg;
55 } metaslab_alloc_trace_t;
58 * Used by the metaslab allocation tracing facility to indicate
59 * error conditions. These errors are stored to the offset member
60 * of the metaslab_alloc_trace_t record and displayed by mdb.
62 typedef enum trace_alloc_type {
63 TRACE_ALLOC_FAILURE = -1ULL,
64 TRACE_TOO_SMALL = -2ULL,
65 TRACE_FORCE_GANG = -3ULL,
66 TRACE_NOT_ALLOCATABLE = -4ULL,
67 TRACE_GROUP_FAILURE = -5ULL,
69 TRACE_CONDENSING = -7ULL,
70 TRACE_VDEV_ERROR = -8ULL
73 #define METASLAB_WEIGHT_PRIMARY (1ULL << 63)
74 #define METASLAB_WEIGHT_SECONDARY (1ULL << 62)
75 #define METASLAB_WEIGHT_TYPE (1ULL << 61)
76 #define METASLAB_ACTIVE_MASK \
77 (METASLAB_WEIGHT_PRIMARY | METASLAB_WEIGHT_SECONDARY)
80 * The metaslab weight is used to encode the amount of free space in a
81 * metaslab, such that the "best" metaslab appears first when sorting the
82 * metaslabs by weight. The weight (and therefore the "best" metaslab) can
83 * be determined in two different ways: by computing a weighted sum of all
84 * the free space in the metaslab (a space based weight) or by counting only
85 * the free segments of the largest size (a segment based weight). We prefer
86 * the segment based weight because it reflects how the free space is
87 * comprised, but we cannot always use it -- legacy pools do not have the
88 * space map histogram information necessary to determine the largest
89 * contiguous regions. Pools that have the space map histogram determine
90 * the segment weight by looking at each bucket in the histogram and
91 * determining the free space whose size in bytes is in the range:
93 * We then encode the largest index, i, that contains regions into the
94 * segment-weighted value.
98 * 64 56 48 40 32 24 16 8 0
99 * +-------+-------+-------+-------+-------+-------+-------+-------+
100 * |PS1| weighted-free space |
101 * +-------+-------+-------+-------+-------+-------+-------+-------+
103 * PS - indicates primary and secondary activation
104 * space - the fragmentation-weighted space
106 * Segment-based weight:
108 * 64 56 48 40 32 24 16 8 0
109 * +-------+-------+-------+-------+-------+-------+-------+-------+
110 * |PS0| idx| count of segments in region |
111 * +-------+-------+-------+-------+-------+-------+-------+-------+
113 * PS - indicates primary and secondary activation
114 * idx - index for the highest bucket in the histogram
115 * count - number of segments in the specified bucket
117 #define WEIGHT_GET_ACTIVE(weight) BF64_GET((weight), 62, 2)
118 #define WEIGHT_SET_ACTIVE(weight, x) BF64_SET((weight), 62, 2, x)
120 #define WEIGHT_IS_SPACEBASED(weight) \
121 ((weight) == 0 || BF64_GET((weight), 61, 1))
122 #define WEIGHT_SET_SPACEBASED(weight) BF64_SET((weight), 61, 1, 1)
125 * These macros are only applicable to segment-based weighting.
127 #define WEIGHT_GET_INDEX(weight) BF64_GET((weight), 55, 6)
128 #define WEIGHT_SET_INDEX(weight, x) BF64_SET((weight), 55, 6, x)
129 #define WEIGHT_GET_COUNT(weight) BF64_GET((weight), 0, 55)
130 #define WEIGHT_SET_COUNT(weight, x) BF64_SET((weight), 0, 55, x)
133 * A metaslab class encompasses a category of allocatable top-level vdevs.
134 * Each top-level vdev is associated with a metaslab group which defines
135 * the allocatable region for that vdev. Examples of these categories include
136 * "normal" for data block allocations (i.e. main pool allocations) or "log"
137 * for allocations designated for intent log devices (i.e. slog devices).
138 * When a block allocation is requested from the SPA it is associated with a
139 * metaslab_class_t, and only top-level vdevs (i.e. metaslab groups) belonging
140 * to the class can be used to satisfy that request. Allocations are done
141 * by traversing the metaslab groups that are linked off of the mc_rotor field.
142 * This rotor points to the next metaslab group where allocations will be
143 * attempted. Allocating a block is a 3 step process -- select the metaslab
144 * group, select the metaslab, and then allocate the block. The metaslab
145 * class defines the low-level block allocator that will be used as the
146 * final step in allocation. These allocators are pluggable allowing each class
147 * to use a block allocator that best suits that class.
149 struct metaslab_class {
152 metaslab_group_t *mc_rotor;
153 metaslab_ops_t *mc_ops;
157 * Track the number of metaslab groups that have been initialized
158 * and can accept allocations. An initialized metaslab group is
159 * one has been completely added to the config (i.e. we have
160 * updated the MOS config and the space has been added to the pool).
165 * Toggle to enable/disable the allocation throttle.
167 boolean_t mc_alloc_throttle_enabled;
170 * The allocation throttle works on a reservation system. Whenever
171 * an asynchronous zio wants to perform an allocation it must
172 * first reserve the number of blocks that it wants to allocate.
173 * If there aren't sufficient slots available for the pending zio
174 * then that I/O is throttled until more slots free up. The current
175 * number of reserved allocations is maintained by the mc_alloc_slots
176 * refcount. The mc_alloc_max_slots value determines the maximum
177 * number of allocations that the system allows. Gang blocks are
178 * allowed to reserve slots even if we've reached the maximum
179 * number of allocations allowed.
181 uint64_t mc_alloc_max_slots;
182 refcount_t mc_alloc_slots;
184 uint64_t mc_alloc_groups; /* # of allocatable groups */
186 uint64_t mc_alloc; /* total allocated space */
187 uint64_t mc_deferred; /* total deferred frees */
188 uint64_t mc_space; /* total space (alloc + free) */
189 uint64_t mc_dspace; /* total deflated space */
190 uint64_t mc_minblocksize;
191 uint64_t mc_histogram[RANGE_TREE_HISTOGRAM_SIZE];
195 * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
196 * of a top-level vdev. They are linked togther to form a circular linked
197 * list and can belong to only one metaslab class. Metaslab groups may become
198 * ineligible for allocations for a number of reasons such as limited free
199 * space, fragmentation, or going offline. When this happens the allocator will
200 * simply find the next metaslab group in the linked list and attempt
201 * to allocate from that group instead.
203 struct metaslab_group {
205 avl_tree_t mg_metaslab_tree;
207 boolean_t mg_allocatable; /* can we allocate? */
210 * A metaslab group is considered to be initialized only after
211 * we have updated the MOS config and added the space to the pool.
212 * We only allow allocation attempts to a metaslab group if it
213 * has been initialized.
215 boolean_t mg_initialized;
217 uint64_t mg_free_capacity; /* percentage free */
219 int64_t mg_activation_count;
220 metaslab_class_t *mg_class;
223 metaslab_group_t *mg_prev;
224 metaslab_group_t *mg_next;
227 * Each metaslab group can handle mg_max_alloc_queue_depth allocations
228 * which are tracked by mg_alloc_queue_depth. It's possible for a
229 * metaslab group to handle more allocations than its max. This
230 * can occur when gang blocks are required or when other groups
231 * are unable to handle their share of allocations.
233 uint64_t mg_max_alloc_queue_depth;
234 refcount_t mg_alloc_queue_depth;
237 * A metalab group that can no longer allocate the minimum block
238 * size will set mg_no_free_space. Once a metaslab group is out
239 * of space then its share of work must be distributed to other
242 boolean_t mg_no_free_space;
244 uint64_t mg_allocations;
245 uint64_t mg_failed_allocations;
246 uint64_t mg_fragmentation;
247 uint64_t mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
251 * This value defines the number of elements in the ms_lbas array. The value
252 * of 64 was chosen as it covers all power of 2 buckets up to UINT64_MAX.
253 * This is the equivalent of highbit(UINT64_MAX).
258 * Each metaslab maintains a set of in-core trees to track metaslab operations.
259 * The in-core free tree (ms_tree) contains the current list of free segments.
260 * As blocks are allocated, the allocated segment are removed from the ms_tree
261 * and added to a per txg allocation tree (ms_alloctree). As blocks are freed,
262 * they are added to the per txg free tree (ms_freetree). These per txg
263 * trees allow us to process all allocations and frees in syncing context
264 * where it is safe to update the on-disk space maps. One additional in-core
265 * tree is maintained to track deferred frees (ms_defertree). Once a block
266 * is freed it will move from the ms_freetree to the ms_defertree. A deferred
267 * free means that a block has been freed but cannot be used by the pool
268 * until TXG_DEFER_SIZE transactions groups later. For example, a block
269 * that is freed in txg 50 will not be available for reallocation until
270 * txg 52 (50 + TXG_DEFER_SIZE). This provides a safety net for uberblock
271 * rollback. A pool could be safely rolled back TXG_DEFERS_SIZE
272 * transactions groups and ensure that no block has been reallocated.
274 * The simplified transition diagram looks like this:
280 * free segment (ms_tree) --------> ms_alloctree ----> (write to space map)
283 * | ms_freetree <--- FREE
287 * +----------- ms_defertree <-------+---------> (write to space map)
290 * Each metaslab's space is tracked in a single space map in the MOS,
291 * which is only updated in syncing context. Each time we sync a txg,
292 * we append the allocs and frees from that txg to the space map.
293 * The pool space is only updated once all metaslabs have finished syncing.
295 * To load the in-core free tree we read the space map from disk.
296 * This object contains a series of alloc and free records that are
297 * combined to make up the list of all free segments in this metaslab. These
298 * segments are represented in-core by the ms_tree and are stored in an
301 * As the space map grows (as a result of the appends) it will
302 * eventually become space-inefficient. When the metaslab's in-core free tree
303 * is zfs_condense_pct/100 times the size of the minimal on-disk
304 * representation, we rewrite it in its minimized form. If a metaslab
305 * needs to condense then we must set the ms_condensing flag to ensure
306 * that allocations are not performed on the metaslab that is being written.
310 kcondvar_t ms_load_cv;
315 uint64_t ms_fragmentation;
317 range_tree_t *ms_alloctree[TXG_SIZE];
318 range_tree_t *ms_freetree[TXG_SIZE];
319 range_tree_t *ms_defertree[TXG_DEFER_SIZE];
320 range_tree_t *ms_tree;
322 boolean_t ms_condensing; /* condensing? */
323 boolean_t ms_condense_wanted;
326 * We must hold both ms_lock and ms_group->mg_lock in order to
330 boolean_t ms_loading;
332 int64_t ms_deferspace; /* sum of ms_defermap[] space */
333 uint64_t ms_weight; /* weight vs. others in group */
334 uint64_t ms_activation_weight; /* activation weight */
337 * Track of whenever a metaslab is selected for loading or allocation.
338 * We use this value to determine how long the metaslab should
341 uint64_t ms_selected_txg;
343 uint64_t ms_alloc_txg; /* last successful alloc (debug only) */
344 uint64_t ms_max_size; /* maximum allocatable size */
347 * The metaslab block allocators can optionally use a size-ordered
348 * range tree and/or an array of LBAs. Not all allocators use
349 * this functionality. The ms_size_tree should always contain the
350 * same number of segments as the ms_tree. The only difference
351 * is that the ms_size_tree is ordered by segment sizes.
353 avl_tree_t ms_size_tree;
354 uint64_t ms_lbas[MAX_LBAS];
356 metaslab_group_t *ms_group; /* metaslab group */
357 avl_node_t ms_group_node; /* node in metaslab group tree */
358 txg_node_t ms_txg_node; /* per-txg dirty metaslab links */
365 #endif /* _SYS_METASLAB_IMPL_H */