metaslab_impl.h revision 2e4c998613148111f2fc5371085331ffb39122ff
/*
* 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
* 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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*/
/*
* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/*
* Copyright (c) 2011, 2014 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>
#ifdef __cplusplus
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 {
};
/*
* 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 {
};
/*
* 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 {
/*
* The metaslab block allocators can optionally use a size-ordered
* 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.
*/
};
#ifdef __cplusplus
}
#endif
#endif /* _SYS_METASLAB_IMPL_H */