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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;
56 } metaslab_alloc_trace_t;
59 * Used by the metaslab allocation tracing facility to indicate
60 * error conditions. These errors are stored to the offset member
61 * of the metaslab_alloc_trace_t record and displayed by mdb.
63 typedef enum trace_alloc_type {
64 TRACE_ALLOC_FAILURE = -1ULL,
65 TRACE_TOO_SMALL = -2ULL,
66 TRACE_FORCE_GANG = -3ULL,
67 TRACE_NOT_ALLOCATABLE = -4ULL,
68 TRACE_GROUP_FAILURE = -5ULL,
70 TRACE_CONDENSING = -7ULL,
71 TRACE_VDEV_ERROR = -8ULL
74 #define METASLAB_WEIGHT_PRIMARY (1ULL << 63)
75 #define METASLAB_WEIGHT_SECONDARY (1ULL << 62)
76 #define METASLAB_WEIGHT_CLAIM (1ULL << 61)
77 #define METASLAB_WEIGHT_TYPE (1ULL << 60)
78 #define METASLAB_ACTIVE_MASK \
79 (METASLAB_WEIGHT_PRIMARY | METASLAB_WEIGHT_SECONDARY | \
80 METASLAB_WEIGHT_CLAIM)
83 * The metaslab weight is used to encode the amount of free space in a
84 * metaslab, such that the "best" metaslab appears first when sorting the
85 * metaslabs by weight. The weight (and therefore the "best" metaslab) can
86 * be determined in two different ways: by computing a weighted sum of all
87 * the free space in the metaslab (a space based weight) or by counting only
88 * the free segments of the largest size (a segment based weight). We prefer
89 * the segment based weight because it reflects how the free space is
90 * comprised, but we cannot always use it -- legacy pools do not have the
91 * space map histogram information necessary to determine the largest
92 * contiguous regions. Pools that have the space map histogram determine
93 * the segment weight by looking at each bucket in the histogram and
94 * determining the free space whose size in bytes is in the range:
96 * We then encode the largest index, i, that contains regions into the
97 * segment-weighted value.
101 * 64 56 48 40 32 24 16 8 0
102 * +-------+-------+-------+-------+-------+-------+-------+-------+
103 * |PSC1| weighted-free space |
104 * +-------+-------+-------+-------+-------+-------+-------+-------+
106 * PS - indicates primary and secondary activation
107 * C - indicates activation for claimed block zio
108 * space - the fragmentation-weighted space
110 * Segment-based weight:
112 * 64 56 48 40 32 24 16 8 0
113 * +-------+-------+-------+-------+-------+-------+-------+-------+
114 * |PSC0| idx| count of segments in region |
115 * +-------+-------+-------+-------+-------+-------+-------+-------+
117 * PS - indicates primary and secondary activation
118 * C - indicates activation for claimed block zio
119 * idx - index for the highest bucket in the histogram
120 * count - number of segments in the specified bucket
122 #define WEIGHT_GET_ACTIVE(weight) BF64_GET((weight), 61, 3)
123 #define WEIGHT_SET_ACTIVE(weight, x) BF64_SET((weight), 61, 3, x)
125 #define WEIGHT_IS_SPACEBASED(weight) \
126 ((weight) == 0 || BF64_GET((weight), 60, 1))
127 #define WEIGHT_SET_SPACEBASED(weight) BF64_SET((weight), 60, 1, 1)
130 * These macros are only applicable to segment-based weighting.
132 #define WEIGHT_GET_INDEX(weight) BF64_GET((weight), 54, 6)
133 #define WEIGHT_SET_INDEX(weight, x) BF64_SET((weight), 54, 6, x)
134 #define WEIGHT_GET_COUNT(weight) BF64_GET((weight), 0, 54)
135 #define WEIGHT_SET_COUNT(weight, x) BF64_SET((weight), 0, 54, x)
138 * A metaslab class encompasses a category of allocatable top-level vdevs.
139 * Each top-level vdev is associated with a metaslab group which defines
140 * the allocatable region for that vdev. Examples of these categories include
141 * "normal" for data block allocations (i.e. main pool allocations) or "log"
142 * for allocations designated for intent log devices (i.e. slog devices).
143 * When a block allocation is requested from the SPA it is associated with a
144 * metaslab_class_t, and only top-level vdevs (i.e. metaslab groups) belonging
145 * to the class can be used to satisfy that request. Allocations are done
146 * by traversing the metaslab groups that are linked off of the mc_rotor field.
147 * This rotor points to the next metaslab group where allocations will be
148 * attempted. Allocating a block is a 3 step process -- select the metaslab
149 * group, select the metaslab, and then allocate the block. The metaslab
150 * class defines the low-level block allocator that will be used as the
151 * final step in allocation. These allocators are pluggable allowing each class
152 * to use a block allocator that best suits that class.
154 struct metaslab_class {
157 metaslab_group_t *mc_rotor;
158 metaslab_ops_t *mc_ops;
162 * Track the number of metaslab groups that have been initialized
163 * and can accept allocations. An initialized metaslab group is
164 * one has been completely added to the config (i.e. we have
165 * updated the MOS config and the space has been added to the pool).
170 * Toggle to enable/disable the allocation throttle.
172 boolean_t mc_alloc_throttle_enabled;
175 * The allocation throttle works on a reservation system. Whenever
176 * an asynchronous zio wants to perform an allocation it must
177 * first reserve the number of blocks that it wants to allocate.
178 * If there aren't sufficient slots available for the pending zio
179 * then that I/O is throttled until more slots free up. The current
180 * number of reserved allocations is maintained by the mc_alloc_slots
181 * refcount. The mc_alloc_max_slots value determines the maximum
182 * number of allocations that the system allows. Gang blocks are
183 * allowed to reserve slots even if we've reached the maximum
184 * number of allocations allowed.
186 uint64_t *mc_alloc_max_slots;
187 refcount_t *mc_alloc_slots;
189 uint64_t mc_alloc_groups; /* # of allocatable groups */
191 uint64_t mc_alloc; /* total allocated space */
192 uint64_t mc_deferred; /* total deferred frees */
193 uint64_t mc_space; /* total space (alloc + free) */
194 uint64_t mc_dspace; /* total deflated space */
195 uint64_t mc_minblocksize;
196 uint64_t mc_histogram[RANGE_TREE_HISTOGRAM_SIZE];
200 * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
201 * of a top-level vdev. They are linked togther to form a circular linked
202 * list and can belong to only one metaslab class. Metaslab groups may become
203 * ineligible for allocations for a number of reasons such as limited free
204 * space, fragmentation, or going offline. When this happens the allocator will
205 * simply find the next metaslab group in the linked list and attempt
206 * to allocate from that group instead.
208 struct metaslab_group {
210 metaslab_t **mg_primaries;
211 metaslab_t **mg_secondaries;
212 avl_tree_t mg_metaslab_tree;
214 boolean_t mg_allocatable; /* can we allocate? */
215 uint64_t mg_ms_ready;
218 * A metaslab group is considered to be initialized only after
219 * we have updated the MOS config and added the space to the pool.
220 * We only allow allocation attempts to a metaslab group if it
221 * has been initialized.
223 boolean_t mg_initialized;
225 uint64_t mg_free_capacity; /* percentage free */
227 int64_t mg_activation_count;
228 metaslab_class_t *mg_class;
231 metaslab_group_t *mg_prev;
232 metaslab_group_t *mg_next;
235 * In order for the allocation throttle to function properly, we cannot
236 * have too many IOs going to each disk by default; the throttle
237 * operates by allocating more work to disks that finish quickly, so
238 * allocating larger chunks to each disk reduces its effectiveness.
239 * However, if the number of IOs going to each allocator is too small,
240 * we will not perform proper aggregation at the vdev_queue layer,
241 * also resulting in decreased performance. Therefore, we will use a
244 * Each allocator in each metaslab group has a current queue depth
245 * (mg_alloc_queue_depth[allocator]) and a current max queue depth
246 * (mg_cur_max_alloc_queue_depth[allocator]), and each metaslab group
247 * has an absolute max queue depth (mg_max_alloc_queue_depth). We
248 * add IOs to an allocator until the mg_alloc_queue_depth for that
249 * allocator hits the cur_max. Every time an IO completes for a given
250 * allocator on a given metaslab group, we increment its cur_max until
251 * it reaches mg_max_alloc_queue_depth. The cur_max resets every txg to
252 * help protect against disks that decrease in performance over time.
254 * It's possible for an allocator to handle more allocations than
255 * its max. This can occur when gang blocks are required or when other
256 * groups are unable to handle their share of allocations.
258 uint64_t mg_max_alloc_queue_depth;
259 uint64_t *mg_cur_max_alloc_queue_depth;
260 refcount_t *mg_alloc_queue_depth;
263 * A metalab group that can no longer allocate the minimum block
264 * size will set mg_no_free_space. Once a metaslab group is out
265 * of space then its share of work must be distributed to other
268 boolean_t mg_no_free_space;
270 uint64_t mg_allocations;
271 uint64_t mg_failed_allocations;
272 uint64_t mg_fragmentation;
273 uint64_t mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
277 * This value defines the number of elements in the ms_lbas array. The value
278 * of 64 was chosen as it covers all power of 2 buckets up to UINT64_MAX.
279 * This is the equivalent of highbit(UINT64_MAX).
284 * Each metaslab maintains a set of in-core trees to track metaslab
285 * operations. The in-core free tree (ms_allocatable) contains the list of
286 * free segments which are eligible for allocation. As blocks are
287 * allocated, the allocated segment are removed from the ms_allocatable and
288 * added to a per txg allocation tree (ms_allocating). As blocks are
289 * freed, they are added to the free tree (ms_freeing). These trees
290 * allow us to process all allocations and frees in syncing context
291 * where it is safe to update the on-disk space maps. An additional set
292 * of in-core trees is maintained to track deferred frees
293 * (ms_defer). Once a block is freed it will move from the
294 * ms_freed to the ms_defer tree. A deferred free means that a block
295 * has been freed but cannot be used by the pool until TXG_DEFER_SIZE
296 * transactions groups later. For example, a block that is freed in txg
297 * 50 will not be available for reallocation until txg 52 (50 +
298 * TXG_DEFER_SIZE). This provides a safety net for uberblock rollback.
299 * A pool could be safely rolled back TXG_DEFERS_SIZE transactions
300 * groups and ensure that no block has been reallocated.
302 * The simplified transition diagram looks like this:
308 * free segment (ms_allocatable) -> ms_allocating[4] -> (write to space map)
310 * | ms_freeing <--- FREE
315 * +-------- ms_defer[2] <-------+-------> (write to space map)
318 * Each metaslab's space is tracked in a single space map in the MOS,
319 * which is only updated in syncing context. Each time we sync a txg,
320 * we append the allocs and frees from that txg to the space map. The
321 * pool space is only updated once all metaslabs have finished syncing.
323 * To load the in-core free tree we read the space map from disk. This
324 * object contains a series of alloc and free records that are combined
325 * to make up the list of all free segments in this metaslab. These
326 * segments are represented in-core by the ms_allocatable and are stored
329 * As the space map grows (as a result of the appends) it will
330 * eventually become space-inefficient. When the metaslab's in-core
331 * free tree is zfs_condense_pct/100 times the size of the minimal
332 * on-disk representation, we rewrite it in its minimized form. If a
333 * metaslab needs to condense then we must set the ms_condensing flag to
334 * ensure that allocations are not performed on the metaslab that is
339 kmutex_t ms_sync_lock;
340 kcondvar_t ms_load_cv;
345 uint64_t ms_fragmentation;
347 range_tree_t *ms_allocating[TXG_SIZE];
348 range_tree_t *ms_allocatable;
351 * The following range trees are accessed only from syncing context.
352 * ms_free*tree only have entries while syncing, and are empty
355 range_tree_t *ms_freeing; /* to free this syncing txg */
356 range_tree_t *ms_freed; /* already freed this syncing txg */
357 range_tree_t *ms_defer[TXG_DEFER_SIZE];
358 range_tree_t *ms_checkpointing; /* to add to the checkpoint */
360 boolean_t ms_condensing; /* condensing? */
361 boolean_t ms_condense_wanted;
362 uint64_t ms_condense_checked_txg;
365 * We must hold both ms_lock and ms_group->mg_lock in order to
369 boolean_t ms_loading;
371 int64_t ms_deferspace; /* sum of ms_defermap[] space */
372 uint64_t ms_weight; /* weight vs. others in group */
373 uint64_t ms_activation_weight; /* activation weight */
376 * Track of whenever a metaslab is selected for loading or allocation.
377 * We use this value to determine how long the metaslab should
380 uint64_t ms_selected_txg;
382 uint64_t ms_alloc_txg; /* last successful alloc (debug only) */
383 uint64_t ms_max_size; /* maximum allocatable size */
386 * -1 if it's not active in an allocator, otherwise set to the allocator
387 * this metaslab is active for.
390 boolean_t ms_primary; /* Only valid if ms_allocator is not -1 */
393 * The metaslab block allocators can optionally use a size-ordered
394 * range tree and/or an array of LBAs. Not all allocators use
395 * this functionality. The ms_allocatable_by_size should always
396 * contain the same number of segments as the ms_allocatable. The
397 * only difference is that the ms_allocatable_by_size is ordered by
400 avl_tree_t ms_allocatable_by_size;
401 uint64_t ms_lbas[MAX_LBAS];
403 metaslab_group_t *ms_group; /* metaslab group */
404 avl_node_t ms_group_node; /* node in metaslab group tree */
405 txg_node_t ms_txg_node; /* per-txg dirty metaslab links */
414 #endif /* _SYS_METASLAB_IMPL_H */