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mirror_zfs/module/zfs/space_map.c
Paul Dagnelie ca5777793e Reduce loaded range tree memory usage 
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
2019-10-09 10:36:03 -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, 2019 by Delphix. All rights reserved.
*/
#include <sys/zfs_context.h>
#include <sys/spa.h>
#include <sys/dmu.h>
#include <sys/dmu_tx.h>
#include <sys/dnode.h>
#include <sys/dsl_pool.h>
#include <sys/zio.h>
#include <sys/space_map.h>
#include <sys/refcount.h>
#include <sys/zfeature.h>
/*
* Note on space map block size:
*
* The data for a given space map can be kept on blocks of any size.
* Larger blocks entail fewer I/O operations, but they also cause the
* DMU to keep more data in-core, and also to waste more I/O bandwidth
* when only a few blocks have changed since the last transaction group.
*/
/*
* Enabled whenever we want to stress test the use of double-word
* space map entries.
*/
boolean_t zfs_force_some_double_word_sm_entries = B_FALSE;
/*
* Override the default indirect block size of 128K, instead use 16K for
* spacemaps (2^14 bytes). This dramatically reduces write inflation since
* appending to a spacemap typically has to write one data block (4KB) and one
* or two indirect blocks (16K-32K, rather than 128K).
*/
int space_map_ibs = 14;
boolean_t
sm_entry_is_debug(uint64_t e)
{
return (SM_PREFIX_DECODE(e) == SM_DEBUG_PREFIX);
}
boolean_t
sm_entry_is_single_word(uint64_t e)
{
uint8_t prefix = SM_PREFIX_DECODE(e);
return (prefix != SM_DEBUG_PREFIX && prefix != SM2_PREFIX);
}
boolean_t
sm_entry_is_double_word(uint64_t e)
{
return (SM_PREFIX_DECODE(e) == SM2_PREFIX);
}
/*
* Iterate through the space map, invoking the callback on each (non-debug)
* space map entry. Stop after reading 'end' bytes of the space map.
*/
int
space_map_iterate(space_map_t *sm, uint64_t end, sm_cb_t callback, void *arg)
{
uint64_t blksz = sm->sm_blksz;
ASSERT3U(blksz, !=, 0);
ASSERT3U(end, <=, space_map_length(sm));
ASSERT0(P2PHASE(end, sizeof (uint64_t)));
dmu_prefetch(sm->sm_os, space_map_object(sm), 0, 0, end,
ZIO_PRIORITY_SYNC_READ);
int error = 0;
for (uint64_t block_base = 0; block_base < end && error == 0;
block_base += blksz) {
dmu_buf_t *db;
error = dmu_buf_hold(sm->sm_os, space_map_object(sm),
block_base, FTAG, &db, DMU_READ_PREFETCH);
if (error != 0)
return (error);
uint64_t *block_start = db->db_data;
uint64_t block_length = MIN(end - block_base, blksz);
uint64_t *block_end = block_start +
(block_length / sizeof (uint64_t));
VERIFY0(P2PHASE(block_length, sizeof (uint64_t)));
VERIFY3U(block_length, !=, 0);
ASSERT3U(blksz, ==, db->db_size);
for (uint64_t *block_cursor = block_start;
block_cursor < block_end && error == 0; block_cursor++) {
uint64_t e = *block_cursor;
if (sm_entry_is_debug(e)) /* Skip debug entries */
continue;
uint64_t raw_offset, raw_run, vdev_id;
maptype_t type;
if (sm_entry_is_single_word(e)) {
type = SM_TYPE_DECODE(e);
vdev_id = SM_NO_VDEVID;
raw_offset = SM_OFFSET_DECODE(e);
raw_run = SM_RUN_DECODE(e);
} else {
/* it is a two-word entry */
ASSERT(sm_entry_is_double_word(e));
raw_run = SM2_RUN_DECODE(e);
vdev_id = SM2_VDEV_DECODE(e);
/* move on to the second word */
block_cursor++;
e = *block_cursor;
VERIFY3P(block_cursor, <=, block_end);
type = SM2_TYPE_DECODE(e);
raw_offset = SM2_OFFSET_DECODE(e);
}
uint64_t entry_offset = (raw_offset << sm->sm_shift) +
sm->sm_start;
uint64_t entry_run = raw_run << sm->sm_shift;
VERIFY0(P2PHASE(entry_offset, 1ULL << sm->sm_shift));
VERIFY0(P2PHASE(entry_run, 1ULL << sm->sm_shift));
ASSERT3U(entry_offset, >=, sm->sm_start);
ASSERT3U(entry_offset, <, sm->sm_start + sm->sm_size);
ASSERT3U(entry_run, <=, sm->sm_size);
ASSERT3U(entry_offset + entry_run, <=,
sm->sm_start + sm->sm_size);
space_map_entry_t sme = {
.sme_type = type,
.sme_vdev = vdev_id,
.sme_offset = entry_offset,
.sme_run = entry_run
};
error = callback(&sme, arg);
}
dmu_buf_rele(db, FTAG);
}
return (error);
}
/*
* Reads the entries from the last block of the space map into
* buf in reverse order. Populates nwords with number of words
* in the last block.
*
* Refer to block comment within space_map_incremental_destroy()
* to understand why this function is needed.
*/
static int
space_map_reversed_last_block_entries(space_map_t *sm, uint64_t *buf,
uint64_t bufsz, uint64_t *nwords)
{
int error = 0;
dmu_buf_t *db;
/*
* Find the offset of the last word in the space map and use
* that to read the last block of the space map with
* dmu_buf_hold().
*/
uint64_t last_word_offset =
sm->sm_phys->smp_length - sizeof (uint64_t);
error = dmu_buf_hold(sm->sm_os, space_map_object(sm), last_word_offset,
FTAG, &db, DMU_READ_NO_PREFETCH);
if (error != 0)
return (error);
ASSERT3U(sm->sm_object, ==, db->db_object);
ASSERT3U(sm->sm_blksz, ==, db->db_size);
ASSERT3U(bufsz, >=, db->db_size);
ASSERT(nwords != NULL);
uint64_t *words = db->db_data;
*nwords =
(sm->sm_phys->smp_length - db->db_offset) / sizeof (uint64_t);
ASSERT3U(*nwords, <=, bufsz / sizeof (uint64_t));
uint64_t n = *nwords;
uint64_t j = n - 1;
for (uint64_t i = 0; i < n; i++) {
uint64_t entry = words[i];
if (sm_entry_is_double_word(entry)) {
/*
* Since we are populating the buffer backwards
* we have to be extra careful and add the two
* words of the double-word entry in the right
* order.
*/
ASSERT3U(j, >, 0);
buf[j - 1] = entry;
i++;
ASSERT3U(i, <, n);
entry = words[i];
buf[j] = entry;
j -= 2;
} else {
ASSERT(sm_entry_is_debug(entry) ||
sm_entry_is_single_word(entry));
buf[j] = entry;
j--;
}
}
/*
* Assert that we wrote backwards all the
* way to the beginning of the buffer.
*/
ASSERT3S(j, ==, -1);
dmu_buf_rele(db, FTAG);
return (error);
}
/*
* Note: This function performs destructive actions - specifically
* it deletes entries from the end of the space map. Thus, callers
* should ensure that they are holding the appropriate locks for
* the space map that they provide.
*/
int
space_map_incremental_destroy(space_map_t *sm, sm_cb_t callback, void *arg,
dmu_tx_t *tx)
{
uint64_t bufsz = MAX(sm->sm_blksz, SPA_MINBLOCKSIZE);
uint64_t *buf = zio_buf_alloc(bufsz);
dmu_buf_will_dirty(sm->sm_dbuf, tx);
/*
* Ideally we would want to iterate from the beginning of the
* space map to the end in incremental steps. The issue with this
* approach is that we don't have any field on-disk that points
* us where to start between each step. We could try zeroing out
* entries that we've destroyed, but this doesn't work either as
* an entry that is 0 is a valid one (ALLOC for range [0x0:0x200]).
*
* As a result, we destroy its entries incrementally starting from
* the end after applying the callback to each of them.
*
* The problem with this approach is that we cannot literally
* iterate through the words in the space map backwards as we
* can't distinguish two-word space map entries from their second
* word. Thus we do the following:
*
* 1] We get all the entries from the last block of the space map
* and put them into a buffer in reverse order. This way the
* last entry comes first in the buffer, the second to last is
* second, etc.
* 2] We iterate through the entries in the buffer and we apply
* the callback to each one. As we move from entry to entry we
* we decrease the size of the space map, deleting effectively
* each entry.
* 3] If there are no more entries in the space map or the callback
* returns a value other than 0, we stop iterating over the
* space map. If there are entries remaining and the callback
* returned 0, we go back to step [1].
*/
int error = 0;
while (space_map_length(sm) > 0 && error == 0) {
uint64_t nwords = 0;
error = space_map_reversed_last_block_entries(sm, buf, bufsz,
&nwords);
if (error != 0)
break;
ASSERT3U(nwords, <=, bufsz / sizeof (uint64_t));
for (uint64_t i = 0; i < nwords; i++) {
uint64_t e = buf[i];
if (sm_entry_is_debug(e)) {
sm->sm_phys->smp_length -= sizeof (uint64_t);
continue;
}
int words = 1;
uint64_t raw_offset, raw_run, vdev_id;
maptype_t type;
if (sm_entry_is_single_word(e)) {
type = SM_TYPE_DECODE(e);
vdev_id = SM_NO_VDEVID;
raw_offset = SM_OFFSET_DECODE(e);
raw_run = SM_RUN_DECODE(e);
} else {
ASSERT(sm_entry_is_double_word(e));
words = 2;
raw_run = SM2_RUN_DECODE(e);
vdev_id = SM2_VDEV_DECODE(e);
/* move to the second word */
i++;
e = buf[i];
ASSERT3P(i, <=, nwords);
type = SM2_TYPE_DECODE(e);
raw_offset = SM2_OFFSET_DECODE(e);
}
uint64_t entry_offset =
(raw_offset << sm->sm_shift) + sm->sm_start;
uint64_t entry_run = raw_run << sm->sm_shift;
VERIFY0(P2PHASE(entry_offset, 1ULL << sm->sm_shift));
VERIFY0(P2PHASE(entry_run, 1ULL << sm->sm_shift));
VERIFY3U(entry_offset, >=, sm->sm_start);
VERIFY3U(entry_offset, <, sm->sm_start + sm->sm_size);
VERIFY3U(entry_run, <=, sm->sm_size);
VERIFY3U(entry_offset + entry_run, <=,
sm->sm_start + sm->sm_size);
space_map_entry_t sme = {
.sme_type = type,
.sme_vdev = vdev_id,
.sme_offset = entry_offset,
.sme_run = entry_run
};
error = callback(&sme, arg);
if (error != 0)
break;
if (type == SM_ALLOC)
sm->sm_phys->smp_alloc -= entry_run;
else
sm->sm_phys->smp_alloc += entry_run;
sm->sm_phys->smp_length -= words * sizeof (uint64_t);
}
}
if (space_map_length(sm) == 0) {
ASSERT0(error);
ASSERT0(space_map_allocated(sm));
}
zio_buf_free(buf, bufsz);
return (error);
}
typedef struct space_map_load_arg {
space_map_t *smla_sm;
range_tree_t *smla_rt;
maptype_t smla_type;
} space_map_load_arg_t;
static int
space_map_load_callback(space_map_entry_t *sme, void *arg)
{
space_map_load_arg_t *smla = arg;
if (sme->sme_type == smla->smla_type) {
VERIFY3U(range_tree_space(smla->smla_rt) + sme->sme_run, <=,
smla->smla_sm->sm_size);
range_tree_add(smla->smla_rt, sme->sme_offset, sme->sme_run);
} else {
range_tree_remove(smla->smla_rt, sme->sme_offset, sme->sme_run);
}
return (0);
}
/*
* Load the spacemap into the rangetree, like space_map_load. But only
* read the first 'length' bytes of the spacemap.
*/
int
space_map_load_length(space_map_t *sm, range_tree_t *rt, maptype_t maptype,
uint64_t length)
{
space_map_load_arg_t smla;
VERIFY0(range_tree_space(rt));
if (maptype == SM_FREE)
range_tree_add(rt, sm->sm_start, sm->sm_size);
smla.smla_rt = rt;
smla.smla_sm = sm;
smla.smla_type = maptype;
int err = space_map_iterate(sm, length,
space_map_load_callback, &smla);
if (err != 0)
range_tree_vacate(rt, NULL, NULL);
return (err);
}
/*
* Load the space map disk into the specified range tree. Segments of maptype
* are added to the range tree, other segment types are removed.
*/
int
space_map_load(space_map_t *sm, range_tree_t *rt, maptype_t maptype)
{
return (space_map_load_length(sm, rt, maptype, space_map_length(sm)));
}
void
space_map_histogram_clear(space_map_t *sm)
{
if (sm->sm_dbuf->db_size != sizeof (space_map_phys_t))
return;
bzero(sm->sm_phys->smp_histogram, sizeof (sm->sm_phys->smp_histogram));
}
boolean_t
space_map_histogram_verify(space_map_t *sm, range_tree_t *rt)
{
/*
* Verify that the in-core range tree does not have any
* ranges smaller than our sm_shift size.
*/
for (int i = 0; i < sm->sm_shift; i++) {
if (rt->rt_histogram[i] != 0)
return (B_FALSE);
}
return (B_TRUE);
}
void
space_map_histogram_add(space_map_t *sm, range_tree_t *rt, dmu_tx_t *tx)
{
int idx = 0;
ASSERT(dmu_tx_is_syncing(tx));
VERIFY3U(space_map_object(sm), !=, 0);
if (sm->sm_dbuf->db_size != sizeof (space_map_phys_t))
return;
dmu_buf_will_dirty(sm->sm_dbuf, tx);
ASSERT(space_map_histogram_verify(sm, rt));
/*
* Transfer the content of the range tree histogram to the space
* map histogram. The space map histogram contains 32 buckets ranging
* between 2^sm_shift to 2^(32+sm_shift-1). The range tree,
* however, can represent ranges from 2^0 to 2^63. Since the space
* map only cares about allocatable blocks (minimum of sm_shift) we
* can safely ignore all ranges in the range tree smaller than sm_shift.
*/
for (int i = sm->sm_shift; i < RANGE_TREE_HISTOGRAM_SIZE; i++) {
/*
* Since the largest histogram bucket in the space map is
* 2^(32+sm_shift-1), we need to normalize the values in
* the range tree for any bucket larger than that size. For
* example given an sm_shift of 9, ranges larger than 2^40
* would get normalized as if they were 1TB ranges. Assume
* the range tree had a count of 5 in the 2^44 (16TB) bucket,
* the calculation below would normalize this to 5 * 2^4 (16).
*/
ASSERT3U(i, >=, idx + sm->sm_shift);
sm->sm_phys->smp_histogram[idx] +=
rt->rt_histogram[i] << (i - idx - sm->sm_shift);
/*
* Increment the space map's index as long as we haven't
* reached the maximum bucket size. Accumulate all ranges
* larger than the max bucket size into the last bucket.
*/
if (idx < SPACE_MAP_HISTOGRAM_SIZE - 1) {
ASSERT3U(idx + sm->sm_shift, ==, i);
idx++;
ASSERT3U(idx, <, SPACE_MAP_HISTOGRAM_SIZE);
}
}
}
static void
space_map_write_intro_debug(space_map_t *sm, maptype_t maptype, dmu_tx_t *tx)
{
dmu_buf_will_dirty(sm->sm_dbuf, tx);
uint64_t dentry = SM_PREFIX_ENCODE(SM_DEBUG_PREFIX) |
SM_DEBUG_ACTION_ENCODE(maptype) |
SM_DEBUG_SYNCPASS_ENCODE(spa_sync_pass(tx->tx_pool->dp_spa)) |
SM_DEBUG_TXG_ENCODE(dmu_tx_get_txg(tx));
dmu_write(sm->sm_os, space_map_object(sm), sm->sm_phys->smp_length,
sizeof (dentry), &dentry, tx);
sm->sm_phys->smp_length += sizeof (dentry);
}
/*
* Writes one or more entries given a segment.
*
* Note: The function may release the dbuf from the pointer initially
* passed to it, and return a different dbuf. Also, the space map's
* dbuf must be dirty for the changes in sm_phys to take effect.
*/
static void
space_map_write_seg(space_map_t *sm, uint64_t rstart, uint64_t rend,
maptype_t maptype, uint64_t vdev_id, uint8_t words, dmu_buf_t **dbp,
void *tag, dmu_tx_t *tx)
{
ASSERT3U(words, !=, 0);
ASSERT3U(words, <=, 2);
/* ensure the vdev_id can be represented by the space map */
ASSERT3U(vdev_id, <=, SM_NO_VDEVID);
/*
* if this is a single word entry, ensure that no vdev was
* specified.
*/
IMPLY(words == 1, vdev_id == SM_NO_VDEVID);
dmu_buf_t *db = *dbp;
ASSERT3U(db->db_size, ==, sm->sm_blksz);
uint64_t *block_base = db->db_data;
uint64_t *block_end = block_base + (sm->sm_blksz / sizeof (uint64_t));
uint64_t *block_cursor = block_base +
(sm->sm_phys->smp_length - db->db_offset) / sizeof (uint64_t);
ASSERT3P(block_cursor, <=, block_end);
uint64_t size = (rend - rstart) >> sm->sm_shift;
uint64_t start = (rstart - sm->sm_start) >> sm->sm_shift;
uint64_t run_max = (words == 2) ? SM2_RUN_MAX : SM_RUN_MAX;
ASSERT3U(rstart, >=, sm->sm_start);
ASSERT3U(rstart, <, sm->sm_start + sm->sm_size);
ASSERT3U(rend - rstart, <=, sm->sm_size);
ASSERT3U(rend, <=, sm->sm_start + sm->sm_size);
while (size != 0) {
ASSERT3P(block_cursor, <=, block_end);
/*
* If we are at the end of this block, flush it and start
* writing again from the beginning.
*/
if (block_cursor == block_end) {
dmu_buf_rele(db, tag);
uint64_t next_word_offset = sm->sm_phys->smp_length;
VERIFY0(dmu_buf_hold(sm->sm_os,
space_map_object(sm), next_word_offset,
tag, &db, DMU_READ_PREFETCH));
dmu_buf_will_dirty(db, tx);
/* update caller's dbuf */
*dbp = db;
ASSERT3U(db->db_size, ==, sm->sm_blksz);
block_base = db->db_data;
block_cursor = block_base;
block_end = block_base +
(db->db_size / sizeof (uint64_t));
}
/*
* If we are writing a two-word entry and we only have one
* word left on this block, just pad it with an empty debug
* entry and write the two-word entry in the next block.
*/
uint64_t *next_entry = block_cursor + 1;
if (next_entry == block_end && words > 1) {
ASSERT3U(words, ==, 2);
*block_cursor = SM_PREFIX_ENCODE(SM_DEBUG_PREFIX) |
SM_DEBUG_ACTION_ENCODE(0) |
SM_DEBUG_SYNCPASS_ENCODE(0) |
SM_DEBUG_TXG_ENCODE(0);
block_cursor++;
sm->sm_phys->smp_length += sizeof (uint64_t);
ASSERT3P(block_cursor, ==, block_end);
continue;
}
uint64_t run_len = MIN(size, run_max);
switch (words) {
case 1:
*block_cursor = SM_OFFSET_ENCODE(start) |
SM_TYPE_ENCODE(maptype) |
SM_RUN_ENCODE(run_len);
block_cursor++;
break;
case 2:
/* write the first word of the entry */
*block_cursor = SM_PREFIX_ENCODE(SM2_PREFIX) |
SM2_RUN_ENCODE(run_len) |
SM2_VDEV_ENCODE(vdev_id);
block_cursor++;
/* move on to the second word of the entry */
ASSERT3P(block_cursor, <, block_end);
*block_cursor = SM2_TYPE_ENCODE(maptype) |
SM2_OFFSET_ENCODE(start);
block_cursor++;
break;
default:
panic("%d-word space map entries are not supported",
words);
break;
}
sm->sm_phys->smp_length += words * sizeof (uint64_t);
start += run_len;
size -= run_len;
}
ASSERT0(size);
}
/*
* Note: The space map's dbuf must be dirty for the changes in sm_phys to
* take effect.
*/
static void
space_map_write_impl(space_map_t *sm, range_tree_t *rt, maptype_t maptype,
uint64_t vdev_id, dmu_tx_t *tx)
{
spa_t *spa = tx->tx_pool->dp_spa;
dmu_buf_t *db;
space_map_write_intro_debug(sm, maptype, tx);
#ifdef DEBUG
/*
* We do this right after we write the intro debug entry
* because the estimate does not take it into account.
*/
uint64_t initial_objsize = sm->sm_phys->smp_length;
uint64_t estimated_growth =
space_map_estimate_optimal_size(sm, rt, SM_NO_VDEVID);
uint64_t estimated_final_objsize = initial_objsize + estimated_growth;
#endif
/*
* Find the offset right after the last word in the space map
* and use that to get a hold of the last block, so we can
* start appending to it.
*/
uint64_t next_word_offset = sm->sm_phys->smp_length;
VERIFY0(dmu_buf_hold(sm->sm_os, space_map_object(sm),
next_word_offset, FTAG, &db, DMU_READ_PREFETCH));
ASSERT3U(db->db_size, ==, sm->sm_blksz);
dmu_buf_will_dirty(db, tx);
zfs_btree_t *t = &rt->rt_root;
zfs_btree_index_t where;
for (range_seg_t *rs = zfs_btree_first(t, &where); rs != NULL;
rs = zfs_btree_next(t, &where, &where)) {
uint64_t offset = (rs_get_start(rs, rt) - sm->sm_start) >>
sm->sm_shift;
uint64_t length = (rs_get_end(rs, rt) - rs_get_start(rs, rt)) >>
sm->sm_shift;
uint8_t words = 1;
/*
* We only write two-word entries when both of the following
* are true:
*
* [1] The feature is enabled.
* [2] The offset or run is too big for a single-word entry,
* or the vdev_id is set (meaning not equal to
* SM_NO_VDEVID).
*
* Note that for purposes of testing we've added the case that
* we write two-word entries occasionally when the feature is
* enabled and zfs_force_some_double_word_sm_entries has been
* set.
*/
if (spa_feature_is_active(spa, SPA_FEATURE_SPACEMAP_V2) &&
(offset >= (1ULL << SM_OFFSET_BITS) ||
length > SM_RUN_MAX ||
vdev_id != SM_NO_VDEVID ||
(zfs_force_some_double_word_sm_entries &&
spa_get_random(100) == 0)))
words = 2;
space_map_write_seg(sm, rs_get_start(rs, rt), rs_get_end(rs,
rt), maptype, vdev_id, words, &db, FTAG, tx);
}
dmu_buf_rele(db, FTAG);
#ifdef DEBUG
/*
* We expect our estimation to be based on the worst case
* scenario [see comment in space_map_estimate_optimal_size()].
* Therefore we expect the actual objsize to be equal or less
* than whatever we estimated it to be.
*/
ASSERT3U(estimated_final_objsize, >=, sm->sm_phys->smp_length);
#endif
}
/*
* Note: This function manipulates the state of the given space map but
* does not hold any locks implicitly. Thus the caller is responsible
* for synchronizing writes to the space map.
*/
void
space_map_write(space_map_t *sm, range_tree_t *rt, maptype_t maptype,
uint64_t vdev_id, dmu_tx_t *tx)
{
ASSERT(dsl_pool_sync_context(dmu_objset_pool(sm->sm_os)));
VERIFY3U(space_map_object(sm), !=, 0);
dmu_buf_will_dirty(sm->sm_dbuf, tx);
/*
* This field is no longer necessary since the in-core space map
* now contains the object number but is maintained for backwards
* compatibility.
*/
sm->sm_phys->smp_object = sm->sm_object;
if (range_tree_is_empty(rt)) {
VERIFY3U(sm->sm_object, ==, sm->sm_phys->smp_object);
return;
}
if (maptype == SM_ALLOC)
sm->sm_phys->smp_alloc += range_tree_space(rt);
else
sm->sm_phys->smp_alloc -= range_tree_space(rt);
uint64_t nodes = zfs_btree_numnodes(&rt->rt_root);
uint64_t rt_space = range_tree_space(rt);
space_map_write_impl(sm, rt, maptype, vdev_id, tx);
/*
* Ensure that the space_map's accounting wasn't changed
* while we were in the middle of writing it out.
*/
VERIFY3U(nodes, ==, zfs_btree_numnodes(&rt->rt_root));
VERIFY3U(range_tree_space(rt), ==, rt_space);
}
static int
space_map_open_impl(space_map_t *sm)
{
int error;
u_longlong_t blocks;
error = dmu_bonus_hold(sm->sm_os, sm->sm_object, sm, &sm->sm_dbuf);
if (error)
return (error);
dmu_object_size_from_db(sm->sm_dbuf, &sm->sm_blksz, &blocks);
sm->sm_phys = sm->sm_dbuf->db_data;
return (0);
}
int
space_map_open(space_map_t **smp, objset_t *os, uint64_t object,
uint64_t start, uint64_t size, uint8_t shift)
{
space_map_t *sm;
int error;
ASSERT(*smp == NULL);
ASSERT(os != NULL);
ASSERT(object != 0);
sm = kmem_alloc(sizeof (space_map_t), KM_SLEEP);
sm->sm_start = start;
sm->sm_size = size;
sm->sm_shift = shift;
sm->sm_os = os;
sm->sm_object = object;
sm->sm_blksz = 0;
sm->sm_dbuf = NULL;
sm->sm_phys = NULL;
error = space_map_open_impl(sm);
if (error != 0) {
space_map_close(sm);
return (error);
}
*smp = sm;
return (0);
}
void
space_map_close(space_map_t *sm)
{
if (sm == NULL)
return;
if (sm->sm_dbuf != NULL)
dmu_buf_rele(sm->sm_dbuf, sm);
sm->sm_dbuf = NULL;
sm->sm_phys = NULL;
kmem_free(sm, sizeof (*sm));
}
void
space_map_truncate(space_map_t *sm, int blocksize, dmu_tx_t *tx)
{
objset_t *os = sm->sm_os;
spa_t *spa = dmu_objset_spa(os);
dmu_object_info_t doi;
ASSERT(dsl_pool_sync_context(dmu_objset_pool(os)));
ASSERT(dmu_tx_is_syncing(tx));
VERIFY3U(dmu_tx_get_txg(tx), <=, spa_final_dirty_txg(spa));
dmu_object_info_from_db(sm->sm_dbuf, &doi);
/*
* If the space map has the wrong bonus size (because
* SPA_FEATURE_SPACEMAP_HISTOGRAM has recently been enabled), or
* the wrong block size (because space_map_blksz has changed),
* free and re-allocate its object with the updated sizes.
*
* Otherwise, just truncate the current object.
*/
if ((spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM) &&
doi.doi_bonus_size != sizeof (space_map_phys_t)) ||
doi.doi_data_block_size != blocksize ||
doi.doi_metadata_block_size != 1 << space_map_ibs) {
zfs_dbgmsg("txg %llu, spa %s, sm %px, reallocating "
"object[%llu]: old bonus %u, old blocksz %u",
dmu_tx_get_txg(tx), spa_name(spa), sm, sm->sm_object,
doi.doi_bonus_size, doi.doi_data_block_size);
space_map_free(sm, tx);
dmu_buf_rele(sm->sm_dbuf, sm);
sm->sm_object = space_map_alloc(sm->sm_os, blocksize, tx);
VERIFY0(space_map_open_impl(sm));
} else {
VERIFY0(dmu_free_range(os, space_map_object(sm), 0, -1ULL, tx));
/*
* If the spacemap is reallocated, its histogram
* will be reset. Do the same in the common case so that
* bugs related to the uncommon case do not go unnoticed.
*/
bzero(sm->sm_phys->smp_histogram,
sizeof (sm->sm_phys->smp_histogram));
}
dmu_buf_will_dirty(sm->sm_dbuf, tx);
sm->sm_phys->smp_length = 0;
sm->sm_phys->smp_alloc = 0;
}
uint64_t
space_map_alloc(objset_t *os, int blocksize, dmu_tx_t *tx)
{
spa_t *spa = dmu_objset_spa(os);
uint64_t object;
int bonuslen;
if (spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM)) {
spa_feature_incr(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM, tx);
bonuslen = sizeof (space_map_phys_t);
ASSERT3U(bonuslen, <=, dmu_bonus_max());
} else {
bonuslen = SPACE_MAP_SIZE_V0;
}
object = dmu_object_alloc_ibs(os, DMU_OT_SPACE_MAP, blocksize,
space_map_ibs, DMU_OT_SPACE_MAP_HEADER, bonuslen, tx);
return (object);
}
void
space_map_free_obj(objset_t *os, uint64_t smobj, dmu_tx_t *tx)
{
spa_t *spa = dmu_objset_spa(os);
if (spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM)) {
dmu_object_info_t doi;
VERIFY0(dmu_object_info(os, smobj, &doi));
if (doi.doi_bonus_size != SPACE_MAP_SIZE_V0) {
spa_feature_decr(spa,
SPA_FEATURE_SPACEMAP_HISTOGRAM, tx);
}
}
VERIFY0(dmu_object_free(os, smobj, tx));
}
void
space_map_free(space_map_t *sm, dmu_tx_t *tx)
{
if (sm == NULL)
return;
space_map_free_obj(sm->sm_os, space_map_object(sm), tx);
sm->sm_object = 0;
}
/*
* Given a range tree, it makes a worst-case estimate of how much
* space would the tree's segments take if they were written to
* the given space map.
*/
uint64_t
space_map_estimate_optimal_size(space_map_t *sm, range_tree_t *rt,
uint64_t vdev_id)
{
spa_t *spa = dmu_objset_spa(sm->sm_os);
uint64_t shift = sm->sm_shift;
uint64_t *histogram = rt->rt_histogram;
uint64_t entries_for_seg = 0;
/*
* In order to get a quick estimate of the optimal size that this
* range tree would have on-disk as a space map, we iterate through
* its histogram buckets instead of iterating through its nodes.
*
* Note that this is a highest-bound/worst-case estimate for the
* following reasons:
*
* 1] We assume that we always add a debug padding for each block
* we write and we also assume that we start at the last word
* of a block attempting to write a two-word entry.
* 2] Rounding up errors due to the way segments are distributed
* in the buckets of the range tree's histogram.
* 3] The activation of zfs_force_some_double_word_sm_entries
* (tunable) when testing.
*
* = Math and Rounding Errors =
*
* rt_histogram[i] bucket of a range tree represents the number
* of entries in [2^i, (2^(i+1))-1] of that range_tree. Given
* that, we want to divide the buckets into groups: Buckets that
* can be represented using a single-word entry, ones that can
* be represented with a double-word entry, and ones that can
* only be represented with multiple two-word entries.
*
* [Note that if the new encoding feature is not enabled there
* are only two groups: single-word entry buckets and multiple
* single-word entry buckets. The information below assumes
* two-word entries enabled, but it can easily applied when
* the feature is not enabled]
*
* To find the highest bucket that can be represented with a
* single-word entry we look at the maximum run that such entry
* can have, which is 2^(SM_RUN_BITS + sm_shift) [remember that
* the run of a space map entry is shifted by sm_shift, thus we
* add it to the exponent]. This way, excluding the value of the
* maximum run that can be represented by a single-word entry,
* all runs that are smaller exist in buckets 0 to
* SM_RUN_BITS + shift - 1.
*
* To find the highest bucket that can be represented with a
* double-word entry, we follow the same approach. Finally, any
* bucket higher than that are represented with multiple two-word
* entries. To be more specific, if the highest bucket whose
* segments can be represented with a single two-word entry is X,
* then bucket X+1 will need 2 two-word entries for each of its
* segments, X+2 will need 4, X+3 will need 8, ...etc.
*
* With all of the above we make our estimation based on bucket
* groups. There is a rounding error though. As we mentioned in
* the example with the one-word entry, the maximum run that can
* be represented in a one-word entry 2^(SM_RUN_BITS + shift) is
* not part of bucket SM_RUN_BITS + shift - 1. Thus, segments of
* that length fall into the next bucket (and bucket group) where
* we start counting two-word entries and this is one more reason
* why the estimated size may end up being bigger than the actual
* size written.
*/
uint64_t size = 0;
uint64_t idx = 0;
if (!spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_V2) ||
(vdev_id == SM_NO_VDEVID && sm->sm_size < SM_OFFSET_MAX)) {
/*
* If we are trying to force some double word entries just
* assume the worst-case of every single word entry being
* written as a double word entry.
*/
uint64_t entry_size =
(spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_V2) &&
zfs_force_some_double_word_sm_entries) ?
(2 * sizeof (uint64_t)) : sizeof (uint64_t);
uint64_t single_entry_max_bucket = SM_RUN_BITS + shift - 1;
for (; idx <= single_entry_max_bucket; idx++)
size += histogram[idx] * entry_size;
if (!spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_V2)) {
for (; idx < RANGE_TREE_HISTOGRAM_SIZE; idx++) {
ASSERT3U(idx, >=, single_entry_max_bucket);
entries_for_seg =
1ULL << (idx - single_entry_max_bucket);
size += histogram[idx] *
entries_for_seg * entry_size;
}
return (size);
}
}
ASSERT(spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_V2));
uint64_t double_entry_max_bucket = SM2_RUN_BITS + shift - 1;
for (; idx <= double_entry_max_bucket; idx++)
size += histogram[idx] * 2 * sizeof (uint64_t);
for (; idx < RANGE_TREE_HISTOGRAM_SIZE; idx++) {
ASSERT3U(idx, >=, double_entry_max_bucket);
entries_for_seg = 1ULL << (idx - double_entry_max_bucket);
size += histogram[idx] *
entries_for_seg * 2 * sizeof (uint64_t);
}
/*
* Assume the worst case where we start with the padding at the end
* of the current block and we add an extra padding entry at the end
* of all subsequent blocks.
*/
size += ((size / sm->sm_blksz) + 1) * sizeof (uint64_t);
return (size);
}
uint64_t
space_map_object(space_map_t *sm)
{
return (sm != NULL ? sm->sm_object : 0);
}
int64_t
space_map_allocated(space_map_t *sm)
{
return (sm != NULL ? sm->sm_phys->smp_alloc : 0);
}
uint64_t
space_map_length(space_map_t *sm)
{
return (sm != NULL ? sm->sm_phys->smp_length : 0);
}
uint64_t
space_map_nblocks(space_map_t *sm)
{
if (sm == NULL)
return (0);
return (DIV_ROUND_UP(space_map_length(sm), sm->sm_blksz));
}
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