/*
* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
- * Copyright (c) 2011 by Delphix. All rights reserved.
+ */
+
+/*
+ * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
*/
#ifndef _SYS_METASLAB_IMPL_H
#include <sys/metaslab.h>
#include <sys/space_map.h>
+#include <sys/range_tree.h>
#include <sys/vdev.h>
#include <sys/txg.h>
#include <sys/avl.h>
extern "C" {
#endif
+/*
+ * Metaslab allocation tracing record.
+ */
+typedef struct metaslab_alloc_trace {
+ list_node_t mat_list_node;
+ metaslab_group_t *mat_mg;
+ metaslab_t *mat_msp;
+ uint64_t mat_size;
+ uint64_t mat_weight;
+ uint32_t mat_dva_id;
+ uint64_t mat_offset;
+} metaslab_alloc_trace_t;
+
+/*
+ * Used by the metaslab allocation tracing facility to indicate
+ * error conditions. These errors are stored to the offset member
+ * of the metaslab_alloc_trace_t record and displayed by mdb.
+ */
+typedef enum trace_alloc_type {
+ TRACE_ALLOC_FAILURE = -1ULL,
+ TRACE_TOO_SMALL = -2ULL,
+ TRACE_FORCE_GANG = -3ULL,
+ TRACE_NOT_ALLOCATABLE = -4ULL,
+ TRACE_GROUP_FAILURE = -5ULL,
+ TRACE_ENOSPC = -6ULL,
+ TRACE_CONDENSING = -7ULL,
+ TRACE_VDEV_ERROR = -8ULL
+} trace_alloc_type_t;
+
+#define METASLAB_WEIGHT_PRIMARY (1ULL << 63)
+#define METASLAB_WEIGHT_SECONDARY (1ULL << 62)
+#define METASLAB_WEIGHT_TYPE (1ULL << 61)
+#define METASLAB_ACTIVE_MASK \
+ (METASLAB_WEIGHT_PRIMARY | METASLAB_WEIGHT_SECONDARY)
+
+/*
+ * The metaslab weight is used to encode the amount of free space in a
+ * metaslab, such that the "best" metaslab appears first when sorting the
+ * metaslabs by weight. The weight (and therefore the "best" metaslab) can
+ * be determined in two different ways: by computing a weighted sum of all
+ * the free space in the metaslab (a space based weight) or by counting only
+ * the free segments of the largest size (a segment based weight). We prefer
+ * the segment based weight because it reflects how the free space is
+ * comprised, but we cannot always use it -- legacy pools do not have the
+ * space map histogram information necessary to determine the largest
+ * contiguous regions. Pools that have the space map histogram determine
+ * the segment weight by looking at each bucket in the histogram and
+ * determining the free space whose size in bytes is in the range:
+ * [2^i, 2^(i+1))
+ * We then encode the largest index, i, that contains regions into the
+ * segment-weighted value.
+ *
+ * Space-based weight:
+ *
+ * 64 56 48 40 32 24 16 8 0
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ * |PS1| weighted-free space |
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ *
+ * PS - indicates primary and secondary activation
+ * space - the fragmentation-weighted space
+ *
+ * Segment-based weight:
+ *
+ * 64 56 48 40 32 24 16 8 0
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ * |PS0| idx| count of segments in region |
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ *
+ * PS - indicates primary and secondary activation
+ * idx - index for the highest bucket in the histogram
+ * count - number of segments in the specified bucket
+ */
+#define WEIGHT_GET_ACTIVE(weight) BF64_GET((weight), 62, 2)
+#define WEIGHT_SET_ACTIVE(weight, x) BF64_SET((weight), 62, 2, x)
+
+#define WEIGHT_IS_SPACEBASED(weight) \
+ ((weight) == 0 || BF64_GET((weight), 61, 1))
+#define WEIGHT_SET_SPACEBASED(weight) BF64_SET((weight), 61, 1, 1)
+
+/*
+ * These macros are only applicable to segment-based weighting.
+ */
+#define WEIGHT_GET_INDEX(weight) BF64_GET((weight), 55, 6)
+#define WEIGHT_SET_INDEX(weight, x) BF64_SET((weight), 55, 6, x)
+#define WEIGHT_GET_COUNT(weight) BF64_GET((weight), 0, 55)
+#define WEIGHT_SET_COUNT(weight, x) BF64_SET((weight), 0, 55, x)
+
+/*
+ * A metaslab class encompasses a category of allocatable top-level vdevs.
+ * Each top-level vdev is associated with a metaslab group which defines
+ * the allocatable region for that vdev. Examples of these categories include
+ * "normal" for data block allocations (i.e. main pool allocations) or "log"
+ * for allocations designated for intent log devices (i.e. slog devices).
+ * When a block allocation is requested from the SPA it is associated with a
+ * metaslab_class_t, and only top-level vdevs (i.e. metaslab groups) belonging
+ * to the class can be used to satisfy that request. Allocations are done
+ * by traversing the metaslab groups that are linked off of the mc_rotor field.
+ * This rotor points to the next metaslab group where allocations will be
+ * attempted. Allocating a block is a 3 step process -- select the metaslab
+ * group, select the metaslab, and then allocate the block. The metaslab
+ * class defines the low-level block allocator that will be used as the
+ * final step in allocation. These allocators are pluggable allowing each class
+ * to use a block allocator that best suits that class.
+ */
struct metaslab_class {
+ kmutex_t mc_lock;
spa_t *mc_spa;
metaslab_group_t *mc_rotor;
- space_map_ops_t *mc_ops;
+ metaslab_ops_t *mc_ops;
uint64_t mc_aliquot;
+
+ /*
+ * Track the number of metaslab groups that have been initialized
+ * and can accept allocations. An initialized metaslab group is
+ * one has been completely added to the config (i.e. we have
+ * updated the MOS config and the space has been added to the pool).
+ */
+ uint64_t mc_groups;
+
+ /*
+ * Toggle to enable/disable the allocation throttle.
+ */
+ boolean_t mc_alloc_throttle_enabled;
+
+ /*
+ * The allocation throttle works on a reservation system. Whenever
+ * an asynchronous zio wants to perform an allocation it must
+ * first reserve the number of blocks that it wants to allocate.
+ * If there aren't sufficient slots available for the pending zio
+ * then that I/O is throttled until more slots free up. The current
+ * number of reserved allocations is maintained by the mc_alloc_slots
+ * refcount. The mc_alloc_max_slots value determines the maximum
+ * number of allocations that the system allows. Gang blocks are
+ * allowed to reserve slots even if we've reached the maximum
+ * number of allocations allowed.
+ */
+ uint64_t mc_alloc_max_slots;
+ refcount_t mc_alloc_slots;
+
+ uint64_t mc_alloc_groups; /* # of allocatable groups */
+
uint64_t mc_alloc; /* total allocated space */
uint64_t mc_deferred; /* total deferred frees */
uint64_t mc_space; /* total space (alloc + free) */
uint64_t mc_dspace; /* total deflated space */
+ uint64_t mc_histogram[RANGE_TREE_HISTOGRAM_SIZE];
};
+/*
+ * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
+ * of a top-level vdev. They are linked together to form a circular linked
+ * list and can belong to only one metaslab class. Metaslab groups may become
+ * ineligible for allocations for a number of reasons such as limited free
+ * space, fragmentation, or going offline. When this happens the allocator will
+ * simply find the next metaslab group in the linked list and attempt
+ * to allocate from that group instead.
+ */
struct metaslab_group {
kmutex_t mg_lock;
avl_tree_t mg_metaslab_tree;
uint64_t mg_aliquot;
- uint64_t mg_bonus_area;
- uint64_t mg_alloc_failures;
+ boolean_t mg_allocatable; /* can we allocate? */
+
+ /*
+ * A metaslab group is considered to be initialized only after
+ * we have updated the MOS config and added the space to the pool.
+ * We only allow allocation attempts to a metaslab group if it
+ * has been initialized.
+ */
+ boolean_t mg_initialized;
+
+ uint64_t mg_free_capacity; /* percentage free */
int64_t mg_bias;
int64_t mg_activation_count;
metaslab_class_t *mg_class;
vdev_t *mg_vd;
+ taskq_t *mg_taskq;
metaslab_group_t *mg_prev;
metaslab_group_t *mg_next;
+
+ /*
+ * Each metaslab group can handle mg_max_alloc_queue_depth allocations
+ * which are tracked by mg_alloc_queue_depth. It's possible for a
+ * metaslab group to handle more allocations than its max. This
+ * can occur when gang blocks are required or when other groups
+ * are unable to handle their share of allocations.
+ */
+ uint64_t mg_max_alloc_queue_depth;
+ refcount_t mg_alloc_queue_depth;
+
+ /*
+ * A metalab group that can no longer allocate the minimum block
+ * size will set mg_no_free_space. Once a metaslab group is out
+ * of space then its share of work must be distributed to other
+ * groups.
+ */
+ boolean_t mg_no_free_space;
+
+ uint64_t mg_allocations;
+ uint64_t mg_failed_allocations;
+ uint64_t mg_fragmentation;
+ uint64_t mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
};
/*
- * Each metaslab's free space is tracked in space map object in the MOS,
+ * This value defines the number of elements in the ms_lbas array. The value
+ * of 64 was chosen as it covers all power of 2 buckets up to UINT64_MAX.
+ * This is the equivalent of highbit(UINT64_MAX).
+ */
+#define MAX_LBAS 64
+
+/*
+ * Each metaslab maintains a set of in-core trees to track metaslab
+ * operations. The in-core free tree (ms_tree) contains the list of
+ * free segments which are eligible for allocation. As blocks are
+ * allocated, the allocated segment are removed from the ms_tree and
+ * added to a per txg allocation tree (ms_alloctree). As blocks are
+ * freed, they are added to the free tree (ms_freeingtree). These trees
+ * allow us to process all allocations and frees in syncing context
+ * where it is safe to update the on-disk space maps. An additional set
+ * of in-core trees is maintained to track deferred frees
+ * (ms_defertree). Once a block is freed it will move from the
+ * ms_freedtree to the ms_defertree. A deferred free means that a block
+ * has been freed but cannot be used by the pool until TXG_DEFER_SIZE
+ * transactions groups later. For example, a block that is freed in txg
+ * 50 will not be available for reallocation until txg 52 (50 +
+ * TXG_DEFER_SIZE). This provides a safety net for uberblock rollback.
+ * A pool could be safely rolled back TXG_DEFERS_SIZE transactions
+ * groups and ensure that no block has been reallocated.
+ *
+ * The simplified transition diagram looks like this:
+ *
+ *
+ * ALLOCATE
+ * |
+ * V
+ * free segment (ms_tree) -----> ms_alloctree[4] ----> (write to space map)
+ * ^
+ * | ms_freeingtree <--- FREE
+ * | |
+ * | v
+ * | ms_freedtree
+ * | |
+ * +-------- ms_defertree[2] <-------+---------> (write to space map)
+ *
+ *
+ * Each metaslab's space is tracked in a single space map in the MOS,
* which is only updated in syncing context. Each time we sync a txg,
- * we append the allocs and frees from that txg to the space map object.
- * When the txg is done syncing, metaslab_sync_done() updates ms_smo
- * to ms_smo_syncing. Everything in ms_smo is always safe to allocate.
+ * we append the allocs and frees from that txg to the space map. The
+ * pool space is only updated once all metaslabs have finished syncing.
+ *
+ * To load the in-core free tree we read the space map from disk. This
+ * object contains a series of alloc and free records that are combined
+ * to make up the list of all free segments in this metaslab. These
+ * segments are represented in-core by the ms_tree and are stored in an
+ * AVL tree.
+ *
+ * As the space map grows (as a result of the appends) it will
+ * eventually become space-inefficient. When the metaslab's in-core
+ * free tree is zfs_condense_pct/100 times the size of the minimal
+ * on-disk representation, we rewrite it in its minimized form. If a
+ * metaslab needs to condense then we must set the ms_condensing flag to
+ * ensure that allocations are not performed on the metaslab that is
+ * being written.
*/
struct metaslab {
- kmutex_t ms_lock; /* metaslab lock */
- space_map_obj_t ms_smo; /* synced space map object */
- space_map_obj_t ms_smo_syncing; /* syncing space map object */
- space_map_t ms_allocmap[TXG_SIZE]; /* allocated this txg */
- space_map_t ms_freemap[TXG_SIZE]; /* freed this txg */
- space_map_t ms_defermap[TXG_DEFER_SIZE]; /* deferred frees */
- space_map_t ms_map; /* in-core free space map */
+ kmutex_t ms_lock;
+ kmutex_t ms_sync_lock;
+ kcondvar_t ms_load_cv;
+ space_map_t *ms_sm;
+ uint64_t ms_id;
+ uint64_t ms_start;
+ uint64_t ms_size;
+ uint64_t ms_fragmentation;
+
+ range_tree_t *ms_alloctree[TXG_SIZE];
+ range_tree_t *ms_tree;
+
+ /*
+ * The following range trees are accessed only from syncing context.
+ * ms_free*tree only have entries while syncing, and are empty
+ * between syncs.
+ */
+ range_tree_t *ms_freeingtree; /* to free this syncing txg */
+ range_tree_t *ms_freedtree; /* already freed this syncing txg */
+ range_tree_t *ms_defertree[TXG_DEFER_SIZE];
+
+ boolean_t ms_condensing; /* condensing? */
+ boolean_t ms_condense_wanted;
+
+ /*
+ * We must hold both ms_lock and ms_group->mg_lock in order to
+ * modify ms_loaded.
+ */
+ boolean_t ms_loaded;
+ boolean_t ms_loading;
+
int64_t ms_deferspace; /* sum of ms_defermap[] space */
uint64_t ms_weight; /* weight vs. others in group */
+ uint64_t ms_activation_weight; /* activation weight */
+
+ /*
+ * Track of whenever a metaslab is selected for loading or allocation.
+ * We use this value to determine how long the metaslab should
+ * stay cached.
+ */
+ uint64_t ms_selected_txg;
+
+ uint64_t ms_alloc_txg; /* last successful alloc (debug only) */
+ uint64_t ms_max_size; /* maximum allocatable size */
+
+ /*
+ * The metaslab block allocators can optionally use a size-ordered
+ * range tree and/or an array of LBAs. Not all allocators use
+ * this functionality. The ms_size_tree should always contain the
+ * same number of segments as the ms_tree. The only difference
+ * is that the ms_size_tree is ordered by segment sizes.
+ */
+ avl_tree_t ms_size_tree;
+ uint64_t ms_lbas[MAX_LBAS];
+
metaslab_group_t *ms_group; /* metaslab group */
avl_node_t ms_group_node; /* node in metaslab group tree */
txg_node_t ms_txg_node; /* per-txg dirty metaslab links */
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