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Motivation
==========
The current space map encoding has the following disadvantages:
[1] Assuming 512 sector size each entry can represent at most 16MB for a segment.
This makes the encoding very inefficient for large regions of space.
[2] As vdev-wide space maps have started to be used by new features (i.e.
device removal, zpool checkpoint) we've started imposing limits in the
vdevs that can be used with them based on the maximum addressable offset
(currently 64PB for a top-level vdev).
New encoding
============
The layout can be found at space_map.h and it remains backwards compatible with
the old one. The introduced two-word entry format, besides extending the limits
imposed by the single-entry layout, also includes a vdev field and some extra
padding after its prefix.
The extra padding after the prefix should is reserved for future usage (e.g.
new prefixes for future encodings or new fields for flags). The new vdev field
not only makes the space maps more self-descriptive, but also opens the doors
for pool-wide space maps (expected to be used in the log spacemap project).
One final important note is that the number of bits used for vdevs is reduced
to 24 bits for blkptrs. That was decided as we don't know of any setups that
use more than 16M vdevs for the time being and we wanted to fit the vdev field
in the space map. In addition that gives us some extra bits in dva_t.
Other references:
=================
The new encoding is also discussed towards the end of the Log Space Map
presentation from 2017's OpenZFS summit.
Link: https://www.youtube.com/watch?v=jj2IxRkl5bQ
Authored by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <gwilson@zfsmail.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Gordon Ross <gwr@nexenta.com>
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/90a56e6d
OpenZFS-issue: https://www.illumos.org/issues/9238
Closes #7665
111 lines
3.2 KiB
C
111 lines
3.2 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) 2011, 2017 by Delphix. All rights reserved.
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* Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
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* Copyright (c) 2013, Joyent, Inc. All rights reserved.
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*/
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#ifndef _ZFEATURE_COMMON_H
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#define _ZFEATURE_COMMON_H
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#include <sys/fs/zfs.h>
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#include <sys/inttypes.h>
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#include <sys/types.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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struct zfeature_info;
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typedef enum spa_feature {
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SPA_FEATURE_NONE = -1,
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SPA_FEATURE_ASYNC_DESTROY,
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SPA_FEATURE_EMPTY_BPOBJ,
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SPA_FEATURE_LZ4_COMPRESS,
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SPA_FEATURE_MULTI_VDEV_CRASH_DUMP,
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SPA_FEATURE_SPACEMAP_HISTOGRAM,
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SPA_FEATURE_ENABLED_TXG,
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SPA_FEATURE_HOLE_BIRTH,
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SPA_FEATURE_EXTENSIBLE_DATASET,
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SPA_FEATURE_EMBEDDED_DATA,
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SPA_FEATURE_BOOKMARKS,
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SPA_FEATURE_FS_SS_LIMIT,
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SPA_FEATURE_LARGE_BLOCKS,
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SPA_FEATURE_LARGE_DNODE,
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SPA_FEATURE_SHA512,
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SPA_FEATURE_SKEIN,
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SPA_FEATURE_EDONR,
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SPA_FEATURE_USEROBJ_ACCOUNTING,
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SPA_FEATURE_ENCRYPTION,
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SPA_FEATURE_PROJECT_QUOTA,
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SPA_FEATURE_DEVICE_REMOVAL,
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SPA_FEATURE_OBSOLETE_COUNTS,
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SPA_FEATURE_POOL_CHECKPOINT,
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SPA_FEATURE_SPACEMAP_V2,
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SPA_FEATURES
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} spa_feature_t;
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#define SPA_FEATURE_DISABLED (-1ULL)
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typedef enum zfeature_flags {
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/* Can open pool readonly even if this feature is not supported. */
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ZFEATURE_FLAG_READONLY_COMPAT = (1 << 0),
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/* Is this feature necessary to read the MOS? */
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ZFEATURE_FLAG_MOS = (1 << 1),
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/* Activate this feature at the same time it is enabled. */
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ZFEATURE_FLAG_ACTIVATE_ON_ENABLE = (1 << 2),
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/* Each dataset has a field set if it has ever used this feature. */
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ZFEATURE_FLAG_PER_DATASET = (1 << 3)
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} zfeature_flags_t;
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typedef struct zfeature_info {
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spa_feature_t fi_feature;
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const char *fi_uname; /* User-facing feature name */
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const char *fi_guid; /* On-disk feature identifier */
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const char *fi_desc; /* Feature description */
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zfeature_flags_t fi_flags;
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/* array of dependencies, terminated by SPA_FEATURE_NONE */
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const spa_feature_t *fi_depends;
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} zfeature_info_t;
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typedef int (zfeature_func_t)(zfeature_info_t *, void *);
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#define ZFS_FEATURE_DEBUG
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extern zfeature_info_t spa_feature_table[SPA_FEATURES];
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extern boolean_t zfeature_is_valid_guid(const char *);
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extern boolean_t zfeature_is_supported(const char *);
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extern int zfeature_lookup_name(const char *, spa_feature_t *);
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extern boolean_t zfeature_depends_on(spa_feature_t, spa_feature_t);
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extern void zpool_feature_init(void);
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#ifdef __cplusplus
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}
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#endif
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#endif /* _ZFEATURE_COMMON_H */
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