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Device removal allocates a new location for each allocated segment on
the disk that's being removed. Each allocation results in one entry in
the mapping table, which maps from old location + length to new
location. When a fragmented disk is removed, this can result in a large
number of mapping entries, and thus a large amount of memory consumed by
the mapping table. In the worst real-world cases, we've seen around 1GB
of RAM per 1TB of storage removed.
We can improve on this situation by allocating larger segments, which
span across both allocated and free regions of the device being removed.
By including free regions in the allocation (and thus mapping), we
reduce the number of mapping entries. For example, if we have a 4K
allocation followed by 1K free and then 4K allocated, we would allocate
4+1+4 = 9KB, and then move the entire region (including allocated and
free parts). In this case we used one mapping where previously we would
have used two, but often the ratio is much higher (up to 20:1 in
real-world use). We then need to mark the regions that were free on the
removing device as free in the new locations, and also obsolete in the
mapping entry.
This method preserves the fragmentation of the removing device, rather
than consolidating its allocated space into a small number of chunks
where possible. But it results in drastic reduction of memory used by
the mapping table - around 20x in the most-fragmented cases.
In the most fragmented real-world cases, this reduces memory used by the
mapping from ~1GB to ~50MB of RAM per 1TB of storage removed. Less
fragmented cases will typically also see around 50-100MB of RAM per 1TB
of storage.
Porting notes:
* Add the following as module parameters:
* zfs_condense_indirect_vdevs_enable
* zfs_condense_max_obsolete_bytes
* Document the following module parameters:
* zfs_condense_indirect_vdevs_enable
* zfs_condense_max_obsolete_bytes
* zfs_condense_min_mapping_bytes
Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
OpenZFS-issue: https://illumos.org/issues/9486
OpenZFS-commit: https://github.com/ahrens/illumos/commit/07152e142e44c
External-issue: DLPX-57962
Closes #7536
126 lines
4.5 KiB
C
126 lines
4.5 KiB
C
/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License (the "License").
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* You may not use this file except in compliance with the License.
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*
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* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
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* or http://www.opensolaris.org/os/licensing.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information: Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*/
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/*
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* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
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* Use is subject to license terms.
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*/
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/*
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* Copyright (c) 2013, 2015 by Delphix. All rights reserved.
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*/
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#ifndef _SYS_RANGE_TREE_H
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#define _SYS_RANGE_TREE_H
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#include <sys/avl.h>
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#include <sys/dmu.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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#define RANGE_TREE_HISTOGRAM_SIZE 64
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typedef struct range_tree_ops range_tree_ops_t;
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/*
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* Note: the range_tree may not be accessed concurrently; consumers
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* must provide external locking if required.
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*/
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typedef struct range_tree {
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avl_tree_t rt_root; /* offset-ordered segment AVL tree */
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uint64_t rt_space; /* sum of all segments in the map */
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uint64_t rt_gap; /* allowable inter-segment gap */
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range_tree_ops_t *rt_ops;
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/* rt_avl_compare should only be set if rt_arg is an AVL tree */
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void *rt_arg;
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int (*rt_avl_compare)(const void *, const void *);
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/*
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* The rt_histogram maintains a histogram of ranges. Each bucket,
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* rt_histogram[i], contains the number of ranges whose size is:
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* 2^i <= size of range in bytes < 2^(i+1)
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*/
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uint64_t rt_histogram[RANGE_TREE_HISTOGRAM_SIZE];
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} range_tree_t;
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typedef struct range_seg {
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avl_node_t rs_node; /* AVL node */
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avl_node_t rs_pp_node; /* AVL picker-private node */
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uint64_t rs_start; /* starting offset of this segment */
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uint64_t rs_end; /* ending offset (non-inclusive) */
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uint64_t rs_fill; /* actual fill if gap mode is on */
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} range_seg_t;
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struct range_tree_ops {
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void (*rtop_create)(range_tree_t *rt, void *arg);
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void (*rtop_destroy)(range_tree_t *rt, void *arg);
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void (*rtop_add)(range_tree_t *rt, range_seg_t *rs, void *arg);
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void (*rtop_remove)(range_tree_t *rt, range_seg_t *rs, void *arg);
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void (*rtop_vacate)(range_tree_t *rt, void *arg);
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};
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typedef void range_tree_func_t(void *arg, uint64_t start, uint64_t size);
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void range_tree_init(void);
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void range_tree_fini(void);
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range_tree_t *range_tree_create_impl(range_tree_ops_t *ops, void *arg,
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int (*avl_compare) (const void *, const void *), uint64_t gap);
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range_tree_t *range_tree_create(range_tree_ops_t *ops, void *arg);
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void range_tree_destroy(range_tree_t *rt);
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boolean_t range_tree_contains(range_tree_t *rt, uint64_t start, uint64_t size);
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range_seg_t *range_tree_find(range_tree_t *rt, uint64_t start, uint64_t size);
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void range_tree_resize_segment(range_tree_t *rt, range_seg_t *rs,
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uint64_t newstart, uint64_t newsize);
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uint64_t range_tree_space(range_tree_t *rt);
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boolean_t range_tree_is_empty(range_tree_t *rt);
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void range_tree_verify(range_tree_t *rt, uint64_t start, uint64_t size);
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void range_tree_swap(range_tree_t **rtsrc, range_tree_t **rtdst);
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void range_tree_stat_verify(range_tree_t *rt);
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uint64_t range_tree_min(range_tree_t *rt);
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uint64_t range_tree_max(range_tree_t *rt);
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uint64_t range_tree_span(range_tree_t *rt);
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void range_tree_add(void *arg, uint64_t start, uint64_t size);
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void range_tree_remove(void *arg, uint64_t start, uint64_t size);
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void range_tree_remove_fill(range_tree_t *rt, uint64_t start, uint64_t size);
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void range_tree_adjust_fill(range_tree_t *rt, range_seg_t *rs, int64_t delta);
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void range_tree_clear(range_tree_t *rt, uint64_t start, uint64_t size);
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void range_tree_vacate(range_tree_t *rt, range_tree_func_t *func, void *arg);
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void range_tree_walk(range_tree_t *rt, range_tree_func_t *func, void *arg);
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range_seg_t *range_tree_first(range_tree_t *rt);
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void rt_avl_create(range_tree_t *rt, void *arg);
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void rt_avl_destroy(range_tree_t *rt, void *arg);
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void rt_avl_add(range_tree_t *rt, range_seg_t *rs, void *arg);
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void rt_avl_remove(range_tree_t *rt, range_seg_t *rs, void *arg);
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void rt_avl_vacate(range_tree_t *rt, void *arg);
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extern struct range_tree_ops rt_avl_ops;
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#ifdef __cplusplus
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}
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#endif
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#endif /* _SYS_RANGE_TREE_H */
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