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ca5777793e
This patch implements a new tree structure for ZFS, and uses it to
store range trees more efficiently.
The new structure is approximately a B-tree, though there are some
small differences from the usual characterizations. The tree has core
nodes and leaf nodes; each contain data elements, which the elements
in the core nodes acting as separators between its children. The
difference between core and leaf nodes is that the core nodes have an
array of children, while leaf nodes don't. Every node in the tree may
be only partially full; in most cases, they are all at least 50% full
(in terms of element count) except for the root node, which can be
less full. Underfull nodes will steal from their neighbors or merge to
remain full enough, while overfull nodes will split in two. The data
elements are contained in tree-controlled buffers; they are copied
into these on insertion, and overwritten on deletion. This means that
the elements are not independently allocated, which reduces overhead,
but also means they can't be shared between trees (and also that
pointers to them are only valid until a side-effectful tree operation
occurs). The overhead varies based on how dense the tree is, but is
usually on the order of about 50% of the element size; the per-node
overheads are very small, and so don't make a significant difference.
The trees can accept arbitrary records; they accept a size and a
comparator to allow them to be used for a variety of purposes.
The new trees replace the AVL trees used in the range trees today.
Currently, the range_seg_t structure contains three 8 byte integers
of payload and two 24 byte avl_tree_node_ts to handle its storage in
both an offset-sorted tree and a size-sorted tree (total size: 64
bytes). In the new model, the range seg structures are usually two 4
byte integers, but a separate one needs to exist for the size-sorted
and offset-sorted tree. Between the raw size, the 50% overhead, and
the double storage, the new btrees are expected to use 8*1.5*2 = 24
bytes per record, or 33.3% as much memory as the AVL trees (this is
for the purposes of storing metaslab range trees; for other purposes,
like scrubs, they use ~50% as much memory).
We reduced the size of the payload in the range segments by teaching
range trees about starting offsets and shifts; since metaslabs have a
fixed starting offset, and they all operate in terms of disk sectors,
we can store the ranges using 4-byte integers as long as the size of
the metaslab divided by the sector size is less than 2^32. For 512-byte
sectors, this is a 2^41 (or 2TB) metaslab, which with the default
settings corresponds to a 256PB disk. 4k sector disks can handle
metaslabs up to 2^46 bytes, or 2^63 byte disks. Since we do not
anticipate disks of this size in the near future, there should be
almost no cases where metaslabs need 64-byte integers to store their
ranges. We do still have the capability to store 64-byte integer ranges
to account for cases where we are storing per-vdev (or per-dnode) trees,
which could reasonably go above the limits discussed. We also do not
store fill information in the compact version of the node, since it
is only used for sorted scrub.
We also optimized the metaslab loading process in various other ways
to offset some inefficiencies in the btree model. While individual
operations (find, insert, remove_from) are faster for the btree than
they are for the avl tree, remove usually requires a find operation,
while in the AVL tree model the element itself suffices. Some clever
changes actually caused an overall speedup in metaslab loading; we use
approximately 40% less cpu to load metaslabs in our tests on Illumos.
Another memory and performance optimization was achieved by changing
what is stored in the size-sorted trees. When a disk is heavily
fragmented, the df algorithm used by default in ZFS will almost always
find a number of small regions in its initial cursor-based search; it
will usually only fall back to the size-sorted tree to find larger
regions. If we increase the size of the cursor-based search slightly,
and don't store segments that are smaller than a tunable size floor
in the size-sorted tree, we can further cut memory usage down to
below 20% of what the AVL trees store. This also results in further
reductions in CPU time spent loading metaslabs.
The 16KiB size floor was chosen because it results in substantial memory
usage reduction while not usually resulting in situations where we can't
find an appropriate chunk with the cursor and are forced to use an
oversized chunk from the size-sorted tree. In addition, even if we do
have to use an oversized chunk from the size-sorted tree, the chunk
would be too small to use for ZIL allocations, so it isn't as big of a
loss as it might otherwise be. And often, more small allocations will
follow the initial one, and the cursor search will now find the
remainder of the chunk we didn't use all of and use it for subsequent
allocations. Practical testing has shown little or no change in
fragmentation as a result of this change.
If the size-sorted tree becomes empty while the offset sorted one still
has entries, it will load all the entries from the offset sorted tree
and disregard the size floor until it is unloaded again. This operation
occurs rarely with the default setting, only on incredibly thoroughly
fragmented pools.
There are some other small changes to zdb to teach it to handle btrees,
but nothing major.
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed by: Sebastien Roy seb@delphix.com
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #9181
145 lines
5.3 KiB
C
145 lines
5.3 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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
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* Copyright (c) 2011, 2018 by Delphix. All rights reserved.
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* Copyright (c) 2017, Intel Corporation.
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*/
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#ifndef _SYS_METASLAB_H
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#define _SYS_METASLAB_H
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#include <sys/spa.h>
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#include <sys/space_map.h>
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#include <sys/txg.h>
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#include <sys/zio.h>
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#include <sys/avl.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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typedef struct metaslab_ops {
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uint64_t (*msop_alloc)(metaslab_t *, uint64_t);
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} metaslab_ops_t;
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extern metaslab_ops_t *zfs_metaslab_ops;
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int metaslab_init(metaslab_group_t *, uint64_t, uint64_t, uint64_t,
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metaslab_t **);
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void metaslab_fini(metaslab_t *);
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void metaslab_set_unflushed_txg(metaslab_t *, uint64_t, dmu_tx_t *);
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void metaslab_set_estimated_condensed_size(metaslab_t *, uint64_t, dmu_tx_t *);
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uint64_t metaslab_unflushed_txg(metaslab_t *);
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uint64_t metaslab_estimated_condensed_size(metaslab_t *);
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int metaslab_sort_by_flushed(const void *, const void *);
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uint64_t metaslab_unflushed_changes_memused(metaslab_t *);
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int metaslab_load(metaslab_t *);
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void metaslab_unload(metaslab_t *);
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boolean_t metaslab_flush(metaslab_t *, dmu_tx_t *);
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uint64_t metaslab_allocated_space(metaslab_t *);
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void metaslab_sync(metaslab_t *, uint64_t);
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void metaslab_sync_done(metaslab_t *, uint64_t);
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void metaslab_sync_reassess(metaslab_group_t *);
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uint64_t metaslab_largest_allocatable(metaslab_t *);
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/*
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* metaslab alloc flags
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*/
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#define METASLAB_HINTBP_FAVOR 0x0
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#define METASLAB_HINTBP_AVOID 0x1
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#define METASLAB_GANG_HEADER 0x2
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#define METASLAB_GANG_CHILD 0x4
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#define METASLAB_ASYNC_ALLOC 0x8
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#define METASLAB_DONT_THROTTLE 0x10
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#define METASLAB_MUST_RESERVE 0x20
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#define METASLAB_FASTWRITE 0x40
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int metaslab_alloc(spa_t *, metaslab_class_t *, uint64_t,
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blkptr_t *, int, uint64_t, blkptr_t *, int, zio_alloc_list_t *, zio_t *,
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int);
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int metaslab_alloc_dva(spa_t *, metaslab_class_t *, uint64_t,
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dva_t *, int, dva_t *, uint64_t, int, zio_alloc_list_t *, int);
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void metaslab_free(spa_t *, const blkptr_t *, uint64_t, boolean_t);
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void metaslab_free_concrete(vdev_t *, uint64_t, uint64_t, boolean_t);
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void metaslab_free_dva(spa_t *, const dva_t *, boolean_t);
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void metaslab_free_impl_cb(uint64_t, vdev_t *, uint64_t, uint64_t, void *);
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void metaslab_unalloc_dva(spa_t *, const dva_t *, uint64_t);
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int metaslab_claim(spa_t *, const blkptr_t *, uint64_t);
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int metaslab_claim_impl(vdev_t *, uint64_t, uint64_t, uint64_t);
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void metaslab_check_free(spa_t *, const blkptr_t *);
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void metaslab_fastwrite_mark(spa_t *, const blkptr_t *);
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void metaslab_fastwrite_unmark(spa_t *, const blkptr_t *);
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void metaslab_stat_init(void);
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void metaslab_stat_fini(void);
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void metaslab_trace_init(zio_alloc_list_t *);
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void metaslab_trace_fini(zio_alloc_list_t *);
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metaslab_class_t *metaslab_class_create(spa_t *, metaslab_ops_t *);
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void metaslab_class_destroy(metaslab_class_t *);
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int metaslab_class_validate(metaslab_class_t *);
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void metaslab_class_histogram_verify(metaslab_class_t *);
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uint64_t metaslab_class_fragmentation(metaslab_class_t *);
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uint64_t metaslab_class_expandable_space(metaslab_class_t *);
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boolean_t metaslab_class_throttle_reserve(metaslab_class_t *, int, int,
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zio_t *, int);
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void metaslab_class_throttle_unreserve(metaslab_class_t *, int, int, zio_t *);
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void metaslab_class_evict_old(metaslab_class_t *, uint64_t);
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uint64_t metaslab_class_get_alloc(metaslab_class_t *);
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uint64_t metaslab_class_get_space(metaslab_class_t *);
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uint64_t metaslab_class_get_dspace(metaslab_class_t *);
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uint64_t metaslab_class_get_deferred(metaslab_class_t *);
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void metaslab_space_update(vdev_t *, metaslab_class_t *,
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int64_t, int64_t, int64_t);
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metaslab_group_t *metaslab_group_create(metaslab_class_t *, vdev_t *, int);
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void metaslab_group_destroy(metaslab_group_t *);
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void metaslab_group_activate(metaslab_group_t *);
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void metaslab_group_passivate(metaslab_group_t *);
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boolean_t metaslab_group_initialized(metaslab_group_t *);
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uint64_t metaslab_group_get_space(metaslab_group_t *);
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void metaslab_group_histogram_verify(metaslab_group_t *);
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uint64_t metaslab_group_fragmentation(metaslab_group_t *);
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void metaslab_group_histogram_remove(metaslab_group_t *, metaslab_t *);
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void metaslab_group_alloc_decrement(spa_t *, uint64_t, void *, int, int,
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boolean_t);
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void metaslab_group_alloc_verify(spa_t *, const blkptr_t *, void *, int);
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void metaslab_recalculate_weight_and_sort(metaslab_t *);
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void metaslab_disable(metaslab_t *);
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void metaslab_enable(metaslab_t *, boolean_t, boolean_t);
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void metaslab_set_selected_txg(metaslab_t *, uint64_t);
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extern int metaslab_debug_load;
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#ifdef __cplusplus
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}
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#endif
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#endif /* _SYS_METASLAB_H */
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