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freebsd-nq/include/sys/space_map.h
Serapheim Dimitropoulos 4d044c4c1d OpenZFS 9238 - ZFS Spacemap Encoding V2 
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
2018-07-05 12:02:34 -07:00

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/*
* 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
* or http://www.opensolaris.org/os/licensing.
* 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]
*
* CDDL HEADER END
*/
/*
* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/*
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
*/
#ifndef _SYS_SPACE_MAP_H
#define _SYS_SPACE_MAP_H
#include <sys/avl.h>
#include <sys/range_tree.h>
#include <sys/dmu.h>
#ifdef __cplusplus
extern "C" {
#endif
/*
* The size of the space map object has increased to include a histogram.
* The SPACE_MAP_SIZE_V0 designates the original size and is used to
* maintain backward compatibility.
*/
#define SPACE_MAP_SIZE_V0 (3 * sizeof (uint64_t))
#define SPACE_MAP_HISTOGRAM_SIZE 32
/*
* The space_map_phys is the on-disk representation of the space map.
* Consumers of space maps should never reference any of the members of this
* structure directly. These members may only be updated in syncing context.
*
* Note the smp_object is no longer used but remains in the structure
* for backward compatibility.
*/
typedef struct space_map_phys {
uint64_t smp_object; /* on-disk space map object */
uint64_t smp_objsize; /* size of the object */
int64_t smp_alloc; /* space allocated from the map */
uint64_t smp_pad[5]; /* reserved */
/*
* The smp_histogram maintains a histogram of free regions. Each
* bucket, smp_histogram[i], contains the number of free regions
* whose size is:
* 2^(i+sm_shift) <= size of free region in bytes < 2^(i+sm_shift+1)
*/
uint64_t smp_histogram[SPACE_MAP_HISTOGRAM_SIZE];
} space_map_phys_t;
/*
* The space map object defines a region of space, its size, how much is
* allocated, and the on-disk object that stores this information.
* Consumers of space maps may only access the members of this structure.
*
* Note: the space_map may not be accessed concurrently; consumers
* must provide external locking if required.
*/
typedef struct space_map {
uint64_t sm_start; /* start of map */
uint64_t sm_size; /* size of map */
uint8_t sm_shift; /* unit shift */
uint64_t sm_length; /* synced length */
int64_t sm_alloc; /* synced space allocated */
objset_t *sm_os; /* objset for this map */
uint64_t sm_object; /* object id for this map */
uint32_t sm_blksz; /* block size for space map */
dmu_buf_t *sm_dbuf; /* space_map_phys_t dbuf */
space_map_phys_t *sm_phys; /* on-disk space map */
} space_map_t;
/*
* debug entry
*
* 2 2 10 50
* +-----+-----+------------+----------------------------------+
* | 1 0 | act | syncpass | txg (lower bits) |
* +-----+-----+------------+----------------------------------+
* 63 62 61 60 59 50 49 0
*
*
* one-word entry
*
* 1 47 1 15
* +-----------------------------------------------------------+
* | 0 | offset (sm_shift units) | type | run |
* +-----------------------------------------------------------+
* 63 62 16 15 14 0
*
*
* two-word entry
*
* 2 2 36 24
* +-----+-----+---------------------------+-------------------+
* | 1 1 | pad | run | vdev |
* +-----+-----+---------------------------+-------------------+
* 63 62 61 60 59 24 23 0
*
* 1 63
* +------+----------------------------------------------------+
* | type | offset |
* +------+----------------------------------------------------+
* 63 62 0
*
* Note that a two-word entry will not straddle a block boundary.
* If necessary, the last word of a block will be padded with a
* debug entry (with act = syncpass = txg = 0).
*/
typedef enum {
SM_ALLOC,
SM_FREE
} maptype_t;
typedef struct space_map_entry {
maptype_t sme_type;
uint32_t sme_vdev; /* max is 2^24-1; SM_NO_VDEVID if not present */
uint64_t sme_offset; /* max is 2^63-1; units of sm_shift */
uint64_t sme_run; /* max is 2^36; units of sm_shift */
} space_map_entry_t;
#define SM_NO_VDEVID (1 << SPA_VDEVBITS)
/* one-word entry constants */
#define SM_DEBUG_PREFIX 2
#define SM_OFFSET_BITS 47
#define SM_RUN_BITS 15
/* two-word entry constants */
#define SM2_PREFIX 3
#define SM2_OFFSET_BITS 63
#define SM2_RUN_BITS 36
#define SM_PREFIX_DECODE(x) BF64_DECODE(x, 62, 2)
#define SM_PREFIX_ENCODE(x) BF64_ENCODE(x, 62, 2)
#define SM_DEBUG_ACTION_DECODE(x) BF64_DECODE(x, 60, 2)
#define SM_DEBUG_ACTION_ENCODE(x) BF64_ENCODE(x, 60, 2)
#define SM_DEBUG_SYNCPASS_DECODE(x) BF64_DECODE(x, 50, 10)
#define SM_DEBUG_SYNCPASS_ENCODE(x) BF64_ENCODE(x, 50, 10)
#define SM_DEBUG_TXG_DECODE(x) BF64_DECODE(x, 0, 50)
#define SM_DEBUG_TXG_ENCODE(x) BF64_ENCODE(x, 0, 50)
#define SM_OFFSET_DECODE(x) BF64_DECODE(x, 16, SM_OFFSET_BITS)
#define SM_OFFSET_ENCODE(x) BF64_ENCODE(x, 16, SM_OFFSET_BITS)
#define SM_TYPE_DECODE(x) BF64_DECODE(x, 15, 1)
#define SM_TYPE_ENCODE(x) BF64_ENCODE(x, 15, 1)
#define SM_RUN_DECODE(x) (BF64_DECODE(x, 0, SM_RUN_BITS) + 1)
#define SM_RUN_ENCODE(x) BF64_ENCODE((x) - 1, 0, SM_RUN_BITS)
#define SM_RUN_MAX SM_RUN_DECODE(~0ULL)
#define SM_OFFSET_MAX SM_OFFSET_DECODE(~0ULL)
#define SM2_RUN_DECODE(x) (BF64_DECODE(x, SPA_VDEVBITS, SM2_RUN_BITS) + 1)
#define SM2_RUN_ENCODE(x) BF64_ENCODE((x) - 1, SPA_VDEVBITS, SM2_RUN_BITS)
#define SM2_VDEV_DECODE(x) BF64_DECODE(x, 0, SPA_VDEVBITS)
#define SM2_VDEV_ENCODE(x) BF64_ENCODE(x, 0, SPA_VDEVBITS)
#define SM2_TYPE_DECODE(x) BF64_DECODE(x, SM2_OFFSET_BITS, 1)
#define SM2_TYPE_ENCODE(x) BF64_ENCODE(x, SM2_OFFSET_BITS, 1)
#define SM2_OFFSET_DECODE(x) BF64_DECODE(x, 0, SM2_OFFSET_BITS)
#define SM2_OFFSET_ENCODE(x) BF64_ENCODE(x, 0, SM2_OFFSET_BITS)
#define SM2_RUN_MAX SM2_RUN_DECODE(~0ULL)
#define SM2_OFFSET_MAX SM2_OFFSET_DECODE(~0ULL)
boolean_t sm_entry_is_debug(uint64_t e);
boolean_t sm_entry_is_single_word(uint64_t e);
boolean_t sm_entry_is_double_word(uint64_t e);
typedef int (*sm_cb_t)(space_map_entry_t *sme, void *arg);
int space_map_load(space_map_t *sm, range_tree_t *rt, maptype_t maptype);
int space_map_iterate(space_map_t *sm, sm_cb_t callback, void *arg);
int space_map_incremental_destroy(space_map_t *sm, sm_cb_t callback, void *arg,
dmu_tx_t *tx);
void space_map_histogram_clear(space_map_t *sm);
void space_map_histogram_add(space_map_t *sm, range_tree_t *rt,
dmu_tx_t *tx);
void space_map_update(space_map_t *sm);
uint64_t space_map_object(space_map_t *sm);
uint64_t space_map_allocated(space_map_t *sm);
uint64_t space_map_length(space_map_t *sm);
void space_map_write(space_map_t *sm, range_tree_t *rt, maptype_t maptype,
uint64_t vdev_id, dmu_tx_t *tx);
uint64_t space_map_estimate_optimal_size(space_map_t *sm, range_tree_t *rt,
uint64_t vdev_id);
void space_map_truncate(space_map_t *sm, int blocksize, dmu_tx_t *tx);
uint64_t space_map_alloc(objset_t *os, int blocksize, dmu_tx_t *tx);
void space_map_free(space_map_t *sm, dmu_tx_t *tx);
void space_map_free_obj(objset_t *os, uint64_t smobj, dmu_tx_t *tx);
int space_map_open(space_map_t **smp, objset_t *os, uint64_t object,
uint64_t start, uint64_t size, uint8_t shift);
void space_map_close(space_map_t *sm);
int64_t space_map_alloc_delta(space_map_t *sm);
#ifdef __cplusplus
}
#endif
#endif /* _SYS_SPACE_MAP_H */
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