OpenZFS 7303 - dynamic metaslab selection

[mirror_zfs.git] / 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 http://www.opensolaris.org/os/licensing.
 * 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]
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 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2011, 2016 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>

#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;
} 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;
        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;
        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];
};

/*
 * 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 current list of free segments.
 * 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 per txg free tree (ms_freetree). These per txg
 * trees allow us to process all allocations and frees in syncing context
 * where it is safe to update the on-disk space maps. One additional in-core
 * tree is maintained to track deferred frees (ms_defertree). Once a block
 * is freed it will move from the ms_freetree 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 ----> (write to space map)
 *         ^
 *         |
 *         |                           ms_freetree <--- FREE
 *         |                                 |
 *         |                                 |
 *         |                                 |
 *         +----------- ms_defertree <-------+---------> (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_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;
        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_freetree[TXG_SIZE];
        range_tree_t    *ms_defertree[TXG_DEFER_SIZE];
        range_tree_t    *ms_tree;

        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 */
};

#ifdef  __cplusplus
}
#endif

#endif  /* _SYS_METASLAB_IMPL_H */