*/
/*
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2014 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
+/*
+ * 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 {
spa_t *mc_spa;
metaslab_group_t *mc_rotor;
- space_map_ops_t *mc_ops;
+ metaslab_ops_t *mc_ops;
uint64_t mc_aliquot;
+ 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];
kmutex_t mc_fastwrite_lock;
};
+/*
+ * Metaslab groups encapsulate all the allocatable regions (i.e. metaslabs)
+ * of a top-level vdev. They are linked togther 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? */
+ 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;
+ uint64_t mg_fragmentation;
+ uint64_t mg_histogram[RANGE_TREE_HISTOGRAM_SIZE];
};
/*
- * Each metaslab maintains an in-core free map (ms_map) that contains the
- * current list of free segments. As blocks are allocated, the allocated
- * segment is removed from the ms_map and added to a per txg allocation map.
- * As blocks are freed, they are added to the per txg free map. These per
- * txg maps allow us to process all allocations and frees in syncing context
- * where it is safe to update the on-disk space maps.
+ * 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:
*
- * Each metaslab's free space is tracked in a space map object in the MOS,
+ *
+ * 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 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 map we read the space map object from disk.
+ * 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_map and are stored in an
+ * segments are represented in-core by the ms_tree and are stored in an
* AVL tree.
*
- * As the space map objects grows (as a result of the appends) it will
- * eventually become space-inefficient. When the space map object is
- * zfs_condense_pct/100 times the size of the minimal on-disk representation,
- * we rewrite it in its minimized form.
+ * 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;
+ kcondvar_t ms_load_cv;
+ space_map_t *ms_sm;
+ metaslab_ops_t *ms_ops;
+ 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;
+ 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_access_txg;
+
+ /*
+ * 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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