FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/include/sys/metaslab_impl.h

     /*
      * CDDL HEADER START
      *
      * The contents of this file are subject to the terms of the
      * Common Development and Distribution License (the "License").
      * You may not use this file except in compliance with the License.
      *
      * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      * or https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    /*
     * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
     * Use is subject to license terms.
     */
    
    /*
     * Copyright (c) 2011, 2019 by Delphix. All rights reserved.
     */
    
    #ifndef _SYS_METASLAB_IMPL_H
    #define _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>
    #include <sys/multilist.h>
    
    #ifdef  __cplusplus
    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;
            int                                     mat_allocator;
    } 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_DISABLED          = -9ULL,
    } trace_alloc_type_t;
    
    #define METASLAB_WEIGHT_PRIMARY         (1ULL << 63)
    #define METASLAB_WEIGHT_SECONDARY       (1ULL << 62)
    #define METASLAB_WEIGHT_CLAIM           (1ULL << 61)
    #define METASLAB_WEIGHT_TYPE            (1ULL << 60)
    #define METASLAB_ACTIVE_MASK            \
            (METASLAB_WEIGHT_PRIMARY | METASLAB_WEIGHT_SECONDARY | \
            METASLAB_WEIGHT_CLAIM)
    
    /*
     * 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
    *      +-------+-------+-------+-------+-------+-------+-------+-------+
    *      |PSC1|                  weighted-free space                     |
    *      +-------+-------+-------+-------+-------+-------+-------+-------+
    *
    *      PS - indicates primary and secondary activation
    *      C - indicates activation for claimed block zio
    *      space - the fragmentation-weighted space
    *
    * Segment-based weight:
    *
    *      64      56      48      40      32      24      16      8       0
    *      +-------+-------+-------+-------+-------+-------+-------+-------+
    *      |PSC0| idx|            count of segments in region              |
    *      +-------+-------+-------+-------+-------+-------+-------+-------+
    *
    *      PS - indicates primary and secondary activation
    *      C - indicates activation for claimed block zio
    *      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), 61, 3)
   #define WEIGHT_SET_ACTIVE(weight, x)            BF64_SET((weight), 61, 3, x)
   
   #define WEIGHT_IS_SPACEBASED(weight)            \
           ((weight) == 0 || BF64_GET((weight), 60, 1))
   #define WEIGHT_SET_SPACEBASED(weight)           BF64_SET((weight), 60, 1, 1)
   
   /*
    * These macros are only applicable to segment-based weighting.
    */
   #define WEIGHT_GET_INDEX(weight)                BF64_GET((weight), 54, 6)
   #define WEIGHT_SET_INDEX(weight, x)             BF64_SET((weight), 54, 6, x)
   #define WEIGHT_GET_COUNT(weight)                BF64_GET((weight), 0, 54)
   #define WEIGHT_SET_COUNT(weight, x)             BF64_SET((weight), 0, 54, x)
   
   /*
    * Per-allocator data structure.
    */
   typedef struct metaslab_class_allocator {
           metaslab_group_t        *mca_rotor;
           uint64_t                mca_aliquot;
   
           /*
            * 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 mca_alloc_slots
            * refcount. The mca_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                mca_alloc_max_slots;
           zfs_refcount_t          mca_alloc_slots;
   } ____cacheline_aligned metaslab_class_allocator_t;
   
   /*
    * 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 mca_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;
           const metaslab_ops_t            *mc_ops;
   
           /*
            * 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;
   
           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];
   
           /*
            * List of all loaded metaslabs in the class, sorted in order of most
            * recent use.
            */
           multilist_t             mc_metaslab_txg_list;
   
           metaslab_class_allocator_t      mc_allocator[];
   };
   
   /*
    * Per-allocator data structure.
    */
   typedef struct metaslab_group_allocator {
           uint64_t        mga_cur_max_alloc_queue_depth;
           zfs_refcount_t  mga_alloc_queue_depth;
           metaslab_t      *mga_primary;
           metaslab_t      *mga_secondary;
   } metaslab_group_allocator_t;
   
   /*
    * 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;
           boolean_t               mg_allocatable;         /* can we allocate? */
           uint64_t                mg_ms_ready;
   
           /*
            * 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;
   
           /*
            * In order for the allocation throttle to function properly, we cannot
            * have too many IOs going to each disk by default; the throttle
            * operates by allocating more work to disks that finish quickly, so
            * allocating larger chunks to each disk reduces its effectiveness.
            * However, if the number of IOs going to each allocator is too small,
            * we will not perform proper aggregation at the vdev_queue layer,
            * also resulting in decreased performance. Therefore, we will use a
            * ramp-up strategy.
            *
            * Each allocator in each metaslab group has a current queue depth
            * (mg_alloc_queue_depth[allocator]) and a current max queue depth
            * (mga_cur_max_alloc_queue_depth[allocator]), and each metaslab group
            * has an absolute max queue depth (mg_max_alloc_queue_depth).  We
            * add IOs to an allocator until the mg_alloc_queue_depth for that
            * allocator hits the cur_max. Every time an IO completes for a given
            * allocator on a given metaslab group, we increment its cur_max until
            * it reaches mg_max_alloc_queue_depth. The cur_max resets every txg to
            * help protect against disks that decrease in performance over time.
            *
            * It's possible for an allocator 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;
   
           /*
            * 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];
   
           int                     mg_ms_disabled;
           boolean_t               mg_disabled_updating;
           kmutex_t                mg_ms_disabled_lock;
           kcondvar_t              mg_ms_disabled_cv;
   
           int                     mg_allocators;
           metaslab_group_allocator_t      mg_allocator[];
   };
   
   /*
    * 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_allocatable) contains the list of
    * free segments which are eligible for allocation.  As blocks are
    * allocated, the allocated segment are removed from the ms_allocatable and
    * added to a per txg allocation tree (ms_allocating).  As blocks are
    * freed, they are added to the free tree (ms_freeing).  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_defer).  Once a block is freed it will move from the
    * ms_freed to the ms_defer tree.  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_allocatable) -> ms_allocating[4] -> (write to space map)
    *         ^
    *         |                        ms_freeing <--- FREE
    *         |                             |
    *         |                             v
    *         |                         ms_freed
    *         |                             |
    *         +-------- ms_defer[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.  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_allocatable 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 {
           /*
            * This is the main lock of the metaslab and its purpose is to
            * coordinate our allocations and frees [e.g metaslab_block_alloc(),
            * metaslab_free_concrete(), ..etc] with our various syncing
            * procedures [e.g. metaslab_sync(), metaslab_sync_done(), ..etc].
            *
            * The lock is also used during some miscellaneous operations like
            * using the metaslab's histogram for the metaslab group's histogram
            * aggregation, or marking the metaslab for initialization.
            */
           kmutex_t        ms_lock;
   
           /*
            * Acquired together with the ms_lock whenever we expect to
            * write to metaslab data on-disk (i.e flushing entries to
            * the metaslab's space map). It helps coordinate readers of
            * the metaslab's space map [see spa_vdev_remove_thread()]
            * with writers [see metaslab_sync() or metaslab_flush()].
            *
            * Note that metaslab_load(), even though a reader, uses
            * a completely different mechanism to deal with the reading
            * of the metaslab's space map based on ms_synced_length. That
            * said, the function still uses the ms_sync_lock after it
            * has read the ms_sm [see relevant comment in metaslab_load()
            * as to why].
            */
           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_allocating[TXG_SIZE];
           range_tree_t    *ms_allocatable;
           uint64_t        ms_allocated_this_txg;
           uint64_t        ms_allocating_total;
   
           /*
            * 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_freeing;    /* to free this syncing txg */
           range_tree_t    *ms_freed;      /* already freed this syncing txg */
           range_tree_t    *ms_defer[TXG_DEFER_SIZE];
           range_tree_t    *ms_checkpointing; /* to add to the checkpoint */
   
           /*
            * The ms_trim tree is the set of allocatable segments which are
            * eligible for trimming. (When the metaslab is loaded, it's a
            * subset of ms_allocatable.)  It's kept in-core as long as the
            * autotrim property is set and is not vacated when the metaslab
            * is unloaded.  Its purpose is to aggregate freed ranges to
            * facilitate efficient trimming.
            */
           range_tree_t    *ms_trim;
   
           boolean_t       ms_condensing;  /* condensing? */
           boolean_t       ms_condense_wanted;
   
           /*
            * The number of consumers which have disabled the metaslab.
            */
           uint64_t        ms_disabled;
   
           /*
            * We must always hold the ms_lock when modifying ms_loaded
            * and ms_loading.
            */
           boolean_t       ms_loaded;
           boolean_t       ms_loading;
           kcondvar_t      ms_flush_cv;
           boolean_t       ms_flushing;
   
           /*
            * The following histograms count entries that are in the
            * metaslab's space map (and its histogram) but are not in
            * ms_allocatable yet, because they are in ms_freed, ms_freeing,
            * or ms_defer[].
            *
            * When the metaslab is not loaded, its ms_weight needs to
            * reflect what is allocatable (i.e. what will be part of
            * ms_allocatable if it is loaded).  The weight is computed from
            * the spacemap histogram, but that includes ranges that are
            * not yet allocatable (because they are in ms_freed,
            * ms_freeing, or ms_defer[]).  Therefore, when calculating the
            * weight, we need to remove those ranges.
            *
            * The ranges in the ms_freed and ms_defer[] range trees are all
            * present in the spacemap.  However, the spacemap may have
            * multiple entries to represent a contiguous range, because it
            * is written across multiple sync passes, but the changes of
            * all sync passes are consolidated into the range trees.
            * Adjacent ranges that are freed in different sync passes of
            * one txg will be represented separately (as 2 or more entries)
            * in the space map (and its histogram), but these adjacent
            * ranges will be consolidated (represented as one entry) in the
            * ms_freed/ms_defer[] range trees (and their histograms).
            *
            * When calculating the weight, we can not simply subtract the
            * range trees' histograms from the spacemap's histogram,
            * because the range trees' histograms may have entries in
            * higher buckets than the spacemap, due to consolidation.
            * Instead we must subtract the exact entries that were added to
            * the spacemap's histogram.  ms_synchist and ms_deferhist[]
            * represent these exact entries, so we can subtract them from
            * the spacemap's histogram when calculating ms_weight.
            *
            * ms_synchist represents the same ranges as ms_freeing +
            * ms_freed, but without consolidation across sync passes.
            *
            * ms_deferhist[i] represents the same ranges as ms_defer[i],
            * but without consolidation across sync passes.
            */
           uint64_t        ms_synchist[SPACE_MAP_HISTOGRAM_SIZE];
           uint64_t        ms_deferhist[TXG_DEFER_SIZE][SPACE_MAP_HISTOGRAM_SIZE];
   
           /*
            * Tracks the exact amount of allocated space of this metaslab
            * (and specifically the metaslab's space map) up to the most
            * recently completed sync pass [see usage in metaslab_sync()].
            */
           uint64_t        ms_allocated_space;
           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;
           /*
            * ms_load/unload_time can be used for performance monitoring
            * (e.g. by dtrace or mdb).
            */
           hrtime_t        ms_load_time;   /* time last loaded */
           hrtime_t        ms_unload_time; /* time last unloaded */
           hrtime_t        ms_selected_time; /* time last allocated from */
   
           uint64_t        ms_alloc_txg;   /* last successful alloc (debug only) */
           uint64_t        ms_max_size;    /* maximum allocatable size     */
   
           /*
            * -1 if it's not active in an allocator, otherwise set to the allocator
            * this metaslab is active for.
            */
           int             ms_allocator;
           boolean_t       ms_primary; /* Only valid if ms_allocator is not -1 */
   
           /*
            * 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_allocatable_by_size should always
            * contain the same number of segments as the ms_allocatable. The
            * only difference is that the ms_allocatable_by_size is ordered by
            * segment sizes.
            */
           zfs_btree_t             ms_allocatable_by_size;
           zfs_btree_t             ms_unflushed_frees_by_size;
           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 */
           avl_node_t      ms_spa_txg_node; /* node in spa_metaslabs_by_txg */
           /*
            * Node in metaslab class's selected txg list
            */
           multilist_node_t        ms_class_txg_node;
   
           /*
            * Allocs and frees that are committed to the vdev log spacemap but
            * not yet to this metaslab's spacemap.
            */
           range_tree_t    *ms_unflushed_allocs;
           range_tree_t    *ms_unflushed_frees;
   
           /*
            * We have flushed entries up to but not including this TXG. In
            * other words, all changes from this TXG and onward should not
            * be in this metaslab's space map and must be read from the
            * log space maps.
            */
           uint64_t        ms_unflushed_txg;
           boolean_t       ms_unflushed_dirty;
   
           /* updated every time we are done syncing the metaslab's space map */
           uint64_t        ms_synced_length;
   
           boolean_t       ms_new;
   };
   
   typedef struct metaslab_unflushed_phys {
           /* on-disk counterpart of ms_unflushed_txg */
           uint64_t        msp_unflushed_txg;
   } metaslab_unflushed_phys_t;
   
   #ifdef  __cplusplus
   }
   #endif
   
   #endif  /* _SYS_METASLAB_IMPL_H */

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