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mirror_zfs/module/zfs/dmu_tx.c
Mateusz Piotrowski a4b21eadec
Add tunable to allow changing micro ZAP's max size 
This change turns `MZAP_MAX_BLKSZ` into a `ZFS_MODULE_PARAM()` called
`zap_micro_max_size`. As a result, we can experiment with different
micro ZAP sizes to improve directory size scaling.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Mateusz Piotrowski <mateuszpiotrowski@klarasystems.com>
Co-authored-by: Toomas Soome <toomas.soome@klarasystems.com>
Signed-off-by: Mateusz Piotrowski <mateuszpiotrowski@klarasystems.com>
Sponsored-by: Wasabi Technology, Inc.
Closes #14292
2023-01-10 13:41:54 -08:00

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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 https://opensource.org/licenses/CDDL-1.0.
* 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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
*/
#include <sys/dmu.h>
#include <sys/dmu_impl.h>
#include <sys/dbuf.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_pool.h>
#include <sys/zap_impl.h>
#include <sys/spa.h>
#include <sys/sa.h>
#include <sys/sa_impl.h>
#include <sys/zfs_context.h>
#include <sys/trace_zfs.h>
typedef void (*dmu_tx_hold_func_t)(dmu_tx_t *tx, struct dnode *dn,
uint64_t arg1, uint64_t arg2);
dmu_tx_stats_t dmu_tx_stats = {
{ "dmu_tx_assigned", KSTAT_DATA_UINT64 },
{ "dmu_tx_delay", KSTAT_DATA_UINT64 },
{ "dmu_tx_error", KSTAT_DATA_UINT64 },
{ "dmu_tx_suspended", KSTAT_DATA_UINT64 },
{ "dmu_tx_group", KSTAT_DATA_UINT64 },
{ "dmu_tx_memory_reserve", KSTAT_DATA_UINT64 },
{ "dmu_tx_memory_reclaim", KSTAT_DATA_UINT64 },
{ "dmu_tx_dirty_throttle", KSTAT_DATA_UINT64 },
{ "dmu_tx_dirty_delay", KSTAT_DATA_UINT64 },
{ "dmu_tx_dirty_over_max", KSTAT_DATA_UINT64 },
{ "dmu_tx_dirty_frees_delay", KSTAT_DATA_UINT64 },
{ "dmu_tx_wrlog_delay", KSTAT_DATA_UINT64 },
{ "dmu_tx_quota", KSTAT_DATA_UINT64 },
};
static kstat_t *dmu_tx_ksp;
dmu_tx_t *
dmu_tx_create_dd(dsl_dir_t *dd)
{
dmu_tx_t *tx = kmem_zalloc(sizeof (dmu_tx_t), KM_SLEEP);
tx->tx_dir = dd;
if (dd != NULL)
tx->tx_pool = dd->dd_pool;
list_create(&tx->tx_holds, sizeof (dmu_tx_hold_t),
offsetof(dmu_tx_hold_t, txh_node));
list_create(&tx->tx_callbacks, sizeof (dmu_tx_callback_t),
offsetof(dmu_tx_callback_t, dcb_node));
tx->tx_start = gethrtime();
return (tx);
}
dmu_tx_t *
dmu_tx_create(objset_t *os)
{
dmu_tx_t *tx = dmu_tx_create_dd(os->os_dsl_dataset->ds_dir);
tx->tx_objset = os;
return (tx);
}
dmu_tx_t *
dmu_tx_create_assigned(struct dsl_pool *dp, uint64_t txg)
{
dmu_tx_t *tx = dmu_tx_create_dd(NULL);
TXG_VERIFY(dp->dp_spa, txg);
tx->tx_pool = dp;
tx->tx_txg = txg;
tx->tx_anyobj = TRUE;
return (tx);
}
int
dmu_tx_is_syncing(dmu_tx_t *tx)
{
return (tx->tx_anyobj);
}
int
dmu_tx_private_ok(dmu_tx_t *tx)
{
return (tx->tx_anyobj);
}
static dmu_tx_hold_t *
dmu_tx_hold_dnode_impl(dmu_tx_t *tx, dnode_t *dn, enum dmu_tx_hold_type type,
uint64_t arg1, uint64_t arg2)
{
dmu_tx_hold_t *txh;
if (dn != NULL) {
(void) zfs_refcount_add(&dn->dn_holds, tx);
if (tx->tx_txg != 0) {
mutex_enter(&dn->dn_mtx);
/*
* dn->dn_assigned_txg == tx->tx_txg doesn't pose a
* problem, but there's no way for it to happen (for
* now, at least).
*/
ASSERT(dn->dn_assigned_txg == 0);
dn->dn_assigned_txg = tx->tx_txg;
(void) zfs_refcount_add(&dn->dn_tx_holds, tx);
mutex_exit(&dn->dn_mtx);
}
}
txh = kmem_zalloc(sizeof (dmu_tx_hold_t), KM_SLEEP);
txh->txh_tx = tx;
txh->txh_dnode = dn;
zfs_refcount_create(&txh->txh_space_towrite);
zfs_refcount_create(&txh->txh_memory_tohold);
txh->txh_type = type;
txh->txh_arg1 = arg1;
txh->txh_arg2 = arg2;
list_insert_tail(&tx->tx_holds, txh);
return (txh);
}
static dmu_tx_hold_t *
dmu_tx_hold_object_impl(dmu_tx_t *tx, objset_t *os, uint64_t object,
enum dmu_tx_hold_type type, uint64_t arg1, uint64_t arg2)
{
dnode_t *dn = NULL;
dmu_tx_hold_t *txh;
int err;
if (object != DMU_NEW_OBJECT) {
err = dnode_hold(os, object, FTAG, &dn);
if (err != 0) {
tx->tx_err = err;
return (NULL);
}
}
txh = dmu_tx_hold_dnode_impl(tx, dn, type, arg1, arg2);
if (dn != NULL)
dnode_rele(dn, FTAG);
return (txh);
}
void
dmu_tx_add_new_object(dmu_tx_t *tx, dnode_t *dn)
{
/*
* If we're syncing, they can manipulate any object anyhow, and
* the hold on the dnode_t can cause problems.
*/
if (!dmu_tx_is_syncing(tx))
(void) dmu_tx_hold_dnode_impl(tx, dn, THT_NEWOBJECT, 0, 0);
}
/*
* This function reads specified data from disk. The specified data will
* be needed to perform the transaction -- i.e, it will be read after
* we do dmu_tx_assign(). There are two reasons that we read the data now
* (before dmu_tx_assign()):
*
* 1. Reading it now has potentially better performance. The transaction
* has not yet been assigned, so the TXG is not held open, and also the
* caller typically has less locks held when calling dmu_tx_hold_*() than
* after the transaction has been assigned. This reduces the lock (and txg)
* hold times, thus reducing lock contention.
*
* 2. It is easier for callers (primarily the ZPL) to handle i/o errors
* that are detected before they start making changes to the DMU state
* (i.e. now). Once the transaction has been assigned, and some DMU
* state has been changed, it can be difficult to recover from an i/o
* error (e.g. to undo the changes already made in memory at the DMU
* layer). Typically code to do so does not exist in the caller -- it
* assumes that the data has already been cached and thus i/o errors are
* not possible.
*
* It has been observed that the i/o initiated here can be a performance
* problem, and it appears to be optional, because we don't look at the
* data which is read. However, removing this read would only serve to
* move the work elsewhere (after the dmu_tx_assign()), where it may
* have a greater impact on performance (in addition to the impact on
* fault tolerance noted above).
*/
static int
dmu_tx_check_ioerr(zio_t *zio, dnode_t *dn, int level, uint64_t blkid)
{
int err;
dmu_buf_impl_t *db;
rw_enter(&dn->dn_struct_rwlock, RW_READER);
db = dbuf_hold_level(dn, level, blkid, FTAG);
rw_exit(&dn->dn_struct_rwlock);
if (db == NULL)
return (SET_ERROR(EIO));
/*
* PARTIAL_FIRST allows caching for uncacheable blocks. It will
* be cleared after dmu_buf_will_dirty() call dbuf_read() again.
*/
err = dbuf_read(db, zio, DB_RF_CANFAIL | DB_RF_NOPREFETCH |
(level == 0 ? DB_RF_PARTIAL_FIRST : 0));
dbuf_rele(db, FTAG);
return (err);
}
static void
dmu_tx_count_write(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
{
dnode_t *dn = txh->txh_dnode;
int err = 0;
if (len == 0)
return;
(void) zfs_refcount_add_many(&txh->txh_space_towrite, len, FTAG);
if (dn == NULL)
return;
/*
* For i/o error checking, read the blocks that will be needed
* to perform the write: the first and last level-0 blocks (if
* they are not aligned, i.e. if they are partial-block writes),
* and all the level-1 blocks.
*/
if (dn->dn_maxblkid == 0) {
if (off < dn->dn_datablksz &&
(off > 0 || len < dn->dn_datablksz)) {
err = dmu_tx_check_ioerr(NULL, dn, 0, 0);
if (err != 0) {
txh->txh_tx->tx_err = err;
}
}
} else {
zio_t *zio = zio_root(dn->dn_objset->os_spa,
NULL, NULL, ZIO_FLAG_CANFAIL);
/* first level-0 block */
uint64_t start = off >> dn->dn_datablkshift;
if (P2PHASE(off, dn->dn_datablksz) || len < dn->dn_datablksz) {
err = dmu_tx_check_ioerr(zio, dn, 0, start);
if (err != 0) {
txh->txh_tx->tx_err = err;
}
}
/* last level-0 block */
uint64_t end = (off + len - 1) >> dn->dn_datablkshift;
if (end != start && end <= dn->dn_maxblkid &&
P2PHASE(off + len, dn->dn_datablksz)) {
err = dmu_tx_check_ioerr(zio, dn, 0, end);
if (err != 0) {
txh->txh_tx->tx_err = err;
}
}
/* level-1 blocks */
if (dn->dn_nlevels > 1) {
int shft = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
for (uint64_t i = (start >> shft) + 1;
i < end >> shft; i++) {
err = dmu_tx_check_ioerr(zio, dn, 1, i);
if (err != 0) {
txh->txh_tx->tx_err = err;
}
}
}
err = zio_wait(zio);
if (err != 0) {
txh->txh_tx->tx_err = err;
}
}
}
static void
dmu_tx_count_dnode(dmu_tx_hold_t *txh)
{
(void) zfs_refcount_add_many(&txh->txh_space_towrite,
DNODE_MIN_SIZE, FTAG);
}
void
dmu_tx_hold_write(dmu_tx_t *tx, uint64_t object, uint64_t off, int len)
{
dmu_tx_hold_t *txh;
ASSERT0(tx->tx_txg);
ASSERT3U(len, <=, DMU_MAX_ACCESS);
ASSERT(len == 0 || UINT64_MAX - off >= len - 1);
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
object, THT_WRITE, off, len);
if (txh != NULL) {
dmu_tx_count_write(txh, off, len);
dmu_tx_count_dnode(txh);
}
}
void
dmu_tx_hold_write_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, int len)
{
dmu_tx_hold_t *txh;
ASSERT0(tx->tx_txg);
ASSERT3U(len, <=, DMU_MAX_ACCESS);
ASSERT(len == 0 || UINT64_MAX - off >= len - 1);
txh = dmu_tx_hold_dnode_impl(tx, dn, THT_WRITE, off, len);
if (txh != NULL) {
dmu_tx_count_write(txh, off, len);
dmu_tx_count_dnode(txh);
}
}
/*
* This function marks the transaction as being a "net free". The end
* result is that refquotas will be disabled for this transaction, and
* this transaction will be able to use half of the pool space overhead
* (see dsl_pool_adjustedsize()). Therefore this function should only
* be called for transactions that we expect will not cause a net increase
* in the amount of space used (but it's OK if that is occasionally not true).
*/
void
dmu_tx_mark_netfree(dmu_tx_t *tx)
{
tx->tx_netfree = B_TRUE;
}
static void
dmu_tx_hold_free_impl(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
{
dmu_tx_t *tx = txh->txh_tx;
dnode_t *dn = txh->txh_dnode;
int err;
ASSERT(tx->tx_txg == 0);
dmu_tx_count_dnode(txh);
if (off >= (dn->dn_maxblkid + 1) * dn->dn_datablksz)
return;
if (len == DMU_OBJECT_END)
len = (dn->dn_maxblkid + 1) * dn->dn_datablksz - off;
dmu_tx_count_dnode(txh);
/*
* For i/o error checking, we read the first and last level-0
* blocks if they are not aligned, and all the level-1 blocks.
*
* Note: dbuf_free_range() assumes that we have not instantiated
* any level-0 dbufs that will be completely freed. Therefore we must
* exercise care to not read or count the first and last blocks
* if they are blocksize-aligned.
*/
if (dn->dn_datablkshift == 0) {
if (off != 0 || len < dn->dn_datablksz)
dmu_tx_count_write(txh, 0, dn->dn_datablksz);
} else {
/* first block will be modified if it is not aligned */
if (!IS_P2ALIGNED(off, 1 << dn->dn_datablkshift))
dmu_tx_count_write(txh, off, 1);
/* last block will be modified if it is not aligned */
if (!IS_P2ALIGNED(off + len, 1 << dn->dn_datablkshift))
dmu_tx_count_write(txh, off + len, 1);
}
/*
* Check level-1 blocks.
*/
if (dn->dn_nlevels > 1) {
int shift = dn->dn_datablkshift + dn->dn_indblkshift -
SPA_BLKPTRSHIFT;
uint64_t start = off >> shift;
uint64_t end = (off + len) >> shift;
ASSERT(dn->dn_indblkshift != 0);
/*
* dnode_reallocate() can result in an object with indirect
* blocks having an odd data block size. In this case,
* just check the single block.
*/
if (dn->dn_datablkshift == 0)
start = end = 0;
zio_t *zio = zio_root(tx->tx_pool->dp_spa,
NULL, NULL, ZIO_FLAG_CANFAIL);
for (uint64_t i = start; i <= end; i++) {
uint64_t ibyte = i << shift;
err = dnode_next_offset(dn, 0, &ibyte, 2, 1, 0);
i = ibyte >> shift;
if (err == ESRCH || i > end)
break;
if (err != 0) {
tx->tx_err = err;
(void) zio_wait(zio);
return;
}
(void) zfs_refcount_add_many(&txh->txh_memory_tohold,
1 << dn->dn_indblkshift, FTAG);
err = dmu_tx_check_ioerr(zio, dn, 1, i);
if (err != 0) {
tx->tx_err = err;
(void) zio_wait(zio);
return;
}
}
err = zio_wait(zio);
if (err != 0) {
tx->tx_err = err;
return;
}
}
}
void
dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off, uint64_t len)
{
dmu_tx_hold_t *txh;
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
object, THT_FREE, off, len);
if (txh != NULL)
(void) dmu_tx_hold_free_impl(txh, off, len);
}
void
dmu_tx_hold_free_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, uint64_t len)
{
dmu_tx_hold_t *txh;
txh = dmu_tx_hold_dnode_impl(tx, dn, THT_FREE, off, len);
if (txh != NULL)
(void) dmu_tx_hold_free_impl(txh, off, len);
}
static void
dmu_tx_hold_zap_impl(dmu_tx_hold_t *txh, const char *name)
{
dmu_tx_t *tx = txh->txh_tx;
dnode_t *dn = txh->txh_dnode;
int err;
extern int zap_micro_max_size;
ASSERT(tx->tx_txg == 0);
dmu_tx_count_dnode(txh);
/*
* Modifying a almost-full microzap is around the worst case (128KB)
*
* If it is a fat zap, the worst case would be 7*16KB=112KB:
* - 3 blocks overwritten: target leaf, ptrtbl block, header block
* - 4 new blocks written if adding:
* - 2 blocks for possibly split leaves,
* - 2 grown ptrtbl blocks
*/
(void) zfs_refcount_add_many(&txh->txh_space_towrite,
zap_micro_max_size, FTAG);
if (dn == NULL)
return;
ASSERT3U(DMU_OT_BYTESWAP(dn->dn_type), ==, DMU_BSWAP_ZAP);
if (dn->dn_maxblkid == 0 || name == NULL) {
/*
* This is a microzap (only one block), or we don't know
* the name. Check the first block for i/o errors.
*/
err = dmu_tx_check_ioerr(NULL, dn, 0, 0);
if (err != 0) {
tx->tx_err = err;
}
} else {
/*
* Access the name so that we'll check for i/o errors to
* the leaf blocks, etc. We ignore ENOENT, as this name
* may not yet exist.
*/
err = zap_lookup_by_dnode(dn, name, 8, 0, NULL);
if (err == EIO || err == ECKSUM || err == ENXIO) {
tx->tx_err = err;
}
}
}
void
dmu_tx_hold_zap(dmu_tx_t *tx, uint64_t object, int add, const char *name)
{
dmu_tx_hold_t *txh;
ASSERT0(tx->tx_txg);
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
object, THT_ZAP, add, (uintptr_t)name);
if (txh != NULL)
dmu_tx_hold_zap_impl(txh, name);
}
void
dmu_tx_hold_zap_by_dnode(dmu_tx_t *tx, dnode_t *dn, int add, const char *name)
{
dmu_tx_hold_t *txh;
ASSERT0(tx->tx_txg);
ASSERT(dn != NULL);
txh = dmu_tx_hold_dnode_impl(tx, dn, THT_ZAP, add, (uintptr_t)name);
if (txh != NULL)
dmu_tx_hold_zap_impl(txh, name);
}
void
dmu_tx_hold_bonus(dmu_tx_t *tx, uint64_t object)
{
dmu_tx_hold_t *txh;
ASSERT(tx->tx_txg == 0);
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
object, THT_BONUS, 0, 0);
if (txh)
dmu_tx_count_dnode(txh);
}
void
dmu_tx_hold_bonus_by_dnode(dmu_tx_t *tx, dnode_t *dn)
{
dmu_tx_hold_t *txh;
ASSERT0(tx->tx_txg);
txh = dmu_tx_hold_dnode_impl(tx, dn, THT_BONUS, 0, 0);
if (txh)
dmu_tx_count_dnode(txh);
}
void
dmu_tx_hold_space(dmu_tx_t *tx, uint64_t space)
{
dmu_tx_hold_t *txh;
ASSERT(tx->tx_txg == 0);
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
DMU_NEW_OBJECT, THT_SPACE, space, 0);
if (txh) {
(void) zfs_refcount_add_many(
&txh->txh_space_towrite, space, FTAG);
}
}
#ifdef ZFS_DEBUG
void
dmu_tx_dirty_buf(dmu_tx_t *tx, dmu_buf_impl_t *db)
{
boolean_t match_object = B_FALSE;
boolean_t match_offset = B_FALSE;
DB_DNODE_ENTER(db);
dnode_t *dn = DB_DNODE(db);
ASSERT(tx->tx_txg != 0);
ASSERT(tx->tx_objset == NULL || dn->dn_objset == tx->tx_objset);
ASSERT3U(dn->dn_object, ==, db->db.db_object);
if (tx->tx_anyobj) {
DB_DNODE_EXIT(db);
return;
}
/* XXX No checking on the meta dnode for now */
if (db->db.db_object == DMU_META_DNODE_OBJECT) {
DB_DNODE_EXIT(db);
return;
}
for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
txh = list_next(&tx->tx_holds, txh)) {
ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
if (txh->txh_dnode == dn && txh->txh_type != THT_NEWOBJECT)
match_object = TRUE;
if (txh->txh_dnode == NULL || txh->txh_dnode == dn) {
int datablkshift = dn->dn_datablkshift ?
dn->dn_datablkshift : SPA_MAXBLOCKSHIFT;
int epbs = dn->dn_indblkshift - SPA_BLKPTRSHIFT;
int shift = datablkshift + epbs * db->db_level;
uint64_t beginblk = shift >= 64 ? 0 :
(txh->txh_arg1 >> shift);
uint64_t endblk = shift >= 64 ? 0 :
((txh->txh_arg1 + txh->txh_arg2 - 1) >> shift);
uint64_t blkid = db->db_blkid;
/* XXX txh_arg2 better not be zero... */
dprintf("found txh type %x beginblk=%llx endblk=%llx\n",
txh->txh_type, (u_longlong_t)beginblk,
(u_longlong_t)endblk);
switch (txh->txh_type) {
case THT_WRITE:
if (blkid >= beginblk && blkid <= endblk)
match_offset = TRUE;
/*
* We will let this hold work for the bonus
* or spill buffer so that we don't need to
* hold it when creating a new object.
*/
if (blkid == DMU_BONUS_BLKID ||
blkid == DMU_SPILL_BLKID)
match_offset = TRUE;
/*
* They might have to increase nlevels,
* thus dirtying the new TLIBs. Or the
* might have to change the block size,
* thus dirying the new lvl=0 blk=0.
*/
if (blkid == 0)
match_offset = TRUE;
break;
case THT_FREE:
/*
* We will dirty all the level 1 blocks in
* the free range and perhaps the first and
* last level 0 block.
*/
if (blkid >= beginblk && (blkid <= endblk ||
txh->txh_arg2 == DMU_OBJECT_END))
match_offset = TRUE;
break;
case THT_SPILL:
if (blkid == DMU_SPILL_BLKID)
match_offset = TRUE;
break;
case THT_BONUS:
if (blkid == DMU_BONUS_BLKID)
match_offset = TRUE;
break;
case THT_ZAP:
match_offset = TRUE;
break;
case THT_NEWOBJECT:
match_object = TRUE;
break;
default:
cmn_err(CE_PANIC, "bad txh_type %d",
txh->txh_type);
}
}
if (match_object && match_offset) {
DB_DNODE_EXIT(db);
return;
}
}
DB_DNODE_EXIT(db);
panic("dirtying dbuf obj=%llx lvl=%u blkid=%llx but not tx_held\n",
(u_longlong_t)db->db.db_object, db->db_level,
(u_longlong_t)db->db_blkid);
}
#endif
/*
* If we can't do 10 iops, something is wrong. Let us go ahead
* and hit zfs_dirty_data_max.
*/
static const hrtime_t zfs_delay_max_ns = 100 * MICROSEC; /* 100 milliseconds */
/*
* We delay transactions when we've determined that the backend storage
* isn't able to accommodate the rate of incoming writes.
*
* If there is already a transaction waiting, we delay relative to when
* that transaction finishes waiting. This way the calculated min_time
* is independent of the number of threads concurrently executing
* transactions.
*
* If we are the only waiter, wait relative to when the transaction
* started, rather than the current time. This credits the transaction for
* "time already served", e.g. reading indirect blocks.
*
* The minimum time for a transaction to take is calculated as:
* min_time = scale * (dirty - min) / (max - dirty)
* min_time is then capped at zfs_delay_max_ns.
*
* The delay has two degrees of freedom that can be adjusted via tunables.
* The percentage of dirty data at which we start to delay is defined by
* zfs_delay_min_dirty_percent. This should typically be at or above
* zfs_vdev_async_write_active_max_dirty_percent so that we only start to
* delay after writing at full speed has failed to keep up with the incoming
* write rate. The scale of the curve is defined by zfs_delay_scale. Roughly
* speaking, this variable determines the amount of delay at the midpoint of
* the curve.
*
* delay
* 10ms +-------------------------------------------------------------*+
* | *|
* 9ms + *+
* | *|
* 8ms + *+
* | * |
* 7ms + * +
* | * |
* 6ms + * +
* | * |
* 5ms + * +
* | * |
* 4ms + * +
* | * |
* 3ms + * +
* | * |
* 2ms + (midpoint) * +
* | | ** |
* 1ms + v *** +
* | zfs_delay_scale ----------> ******** |
* 0 +-------------------------------------*********----------------+
* 0% <- zfs_dirty_data_max -> 100%
*
* Note that since the delay is added to the outstanding time remaining on the
* most recent transaction, the delay is effectively the inverse of IOPS.
* Here the midpoint of 500us translates to 2000 IOPS. The shape of the curve
* was chosen such that small changes in the amount of accumulated dirty data
* in the first 3/4 of the curve yield relatively small differences in the
* amount of delay.
*
* The effects can be easier to understand when the amount of delay is
* represented on a log scale:
*
* delay
* 100ms +-------------------------------------------------------------++
* + +
* | |
* + *+
* 10ms + *+
* + ** +
* | (midpoint) ** |
* + | ** +
* 1ms + v **** +
* + zfs_delay_scale ----------> ***** +
* | **** |
* + **** +
* 100us + ** +
* + * +
* | * |
* + * +
* 10us + * +
* + +
* | |
* + +
* +--------------------------------------------------------------+
* 0% <- zfs_dirty_data_max -> 100%
*
* Note here that only as the amount of dirty data approaches its limit does
* the delay start to increase rapidly. The goal of a properly tuned system
* should be to keep the amount of dirty data out of that range by first
* ensuring that the appropriate limits are set for the I/O scheduler to reach
* optimal throughput on the backend storage, and then by changing the value
* of zfs_delay_scale to increase the steepness of the curve.
*/
static void
dmu_tx_delay(dmu_tx_t *tx, uint64_t dirty)
{
dsl_pool_t *dp = tx->tx_pool;
uint64_t delay_min_bytes, wrlog;
hrtime_t wakeup, tx_time = 0, now;
/* Calculate minimum transaction time for the dirty data amount. */
delay_min_bytes =
zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
if (dirty > delay_min_bytes) {
/*
* The caller has already waited until we are under the max.
* We make them pass us the amount of dirty data so we don't
* have to handle the case of it being >= the max, which
* could cause a divide-by-zero if it's == the max.
*/
ASSERT3U(dirty, <, zfs_dirty_data_max);
tx_time = zfs_delay_scale * (dirty - delay_min_bytes) /
(zfs_dirty_data_max - dirty);
}
/* Calculate minimum transaction time for the TX_WRITE log size. */
wrlog = aggsum_upper_bound(&dp->dp_wrlog_total);
delay_min_bytes =
zfs_wrlog_data_max * zfs_delay_min_dirty_percent / 100;
if (wrlog >= zfs_wrlog_data_max) {
tx_time = zfs_delay_max_ns;
} else if (wrlog > delay_min_bytes) {
tx_time = MAX(zfs_delay_scale * (wrlog - delay_min_bytes) /
(zfs_wrlog_data_max - wrlog), tx_time);
}
if (tx_time == 0)
return;
tx_time = MIN(tx_time, zfs_delay_max_ns);
now = gethrtime();
if (now > tx->tx_start + tx_time)
return;
DTRACE_PROBE3(delay__mintime, dmu_tx_t *, tx, uint64_t, dirty,
uint64_t, tx_time);
mutex_enter(&dp->dp_lock);
wakeup = MAX(tx->tx_start + tx_time, dp->dp_last_wakeup + tx_time);
dp->dp_last_wakeup = wakeup;
mutex_exit(&dp->dp_lock);
zfs_sleep_until(wakeup);
}
/*
* This routine attempts to assign the transaction to a transaction group.
* To do so, we must determine if there is sufficient free space on disk.
*
* If this is a "netfree" transaction (i.e. we called dmu_tx_mark_netfree()
* on it), then it is assumed that there is sufficient free space,
* unless there's insufficient slop space in the pool (see the comment
* above spa_slop_shift in spa_misc.c).
*
* If it is not a "netfree" transaction, then if the data already on disk
* is over the allowed usage (e.g. quota), this will fail with EDQUOT or
* ENOSPC. Otherwise, if the current rough estimate of pending changes,
* plus the rough estimate of this transaction's changes, may exceed the
* allowed usage, then this will fail with ERESTART, which will cause the
* caller to wait for the pending changes to be written to disk (by waiting
* for the next TXG to open), and then check the space usage again.
*
* The rough estimate of pending changes is comprised of the sum of:
*
* - this transaction's holds' txh_space_towrite
*
* - dd_tempreserved[], which is the sum of in-flight transactions'
* holds' txh_space_towrite (i.e. those transactions that have called
* dmu_tx_assign() but not yet called dmu_tx_commit()).
*
* - dd_space_towrite[], which is the amount of dirtied dbufs.
*
* Note that all of these values are inflated by spa_get_worst_case_asize(),
* which means that we may get ERESTART well before we are actually in danger
* of running out of space, but this also mitigates any small inaccuracies
* in the rough estimate (e.g. txh_space_towrite doesn't take into account
* indirect blocks, and dd_space_towrite[] doesn't take into account changes
* to the MOS).
*
* Note that due to this algorithm, it is possible to exceed the allowed
* usage by one transaction. Also, as we approach the allowed usage,
* we will allow a very limited amount of changes into each TXG, thus
* decreasing performance.
*/
static int
dmu_tx_try_assign(dmu_tx_t *tx, uint64_t txg_how)
{
spa_t *spa = tx->tx_pool->dp_spa;
ASSERT0(tx->tx_txg);
if (tx->tx_err) {
DMU_TX_STAT_BUMP(dmu_tx_error);
return (tx->tx_err);
}
if (spa_suspended(spa)) {
DMU_TX_STAT_BUMP(dmu_tx_suspended);
/*
* If the user has indicated a blocking failure mode
* then return ERESTART which will block in dmu_tx_wait().
* Otherwise, return EIO so that an error can get
* propagated back to the VOP calls.
*
* Note that we always honor the txg_how flag regardless
* of the failuremode setting.
*/
if (spa_get_failmode(spa) == ZIO_FAILURE_MODE_CONTINUE &&
!(txg_how & TXG_WAIT))
return (SET_ERROR(EIO));
return (SET_ERROR(ERESTART));
}
if (!tx->tx_dirty_delayed &&
dsl_pool_need_wrlog_delay(tx->tx_pool)) {
tx->tx_wait_dirty = B_TRUE;
DMU_TX_STAT_BUMP(dmu_tx_wrlog_delay);
return (SET_ERROR(ERESTART));
}
if (!tx->tx_dirty_delayed &&
dsl_pool_need_dirty_delay(tx->tx_pool)) {
tx->tx_wait_dirty = B_TRUE;
DMU_TX_STAT_BUMP(dmu_tx_dirty_delay);
return (SET_ERROR(ERESTART));
}
tx->tx_txg = txg_hold_open(tx->tx_pool, &tx->tx_txgh);
tx->tx_needassign_txh = NULL;
/*
* NB: No error returns are allowed after txg_hold_open, but
* before processing the dnode holds, due to the
* dmu_tx_unassign() logic.
*/
uint64_t towrite = 0;
uint64_t tohold = 0;
for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
txh = list_next(&tx->tx_holds, txh)) {
dnode_t *dn = txh->txh_dnode;
if (dn != NULL) {
/*
* This thread can't hold the dn_struct_rwlock
* while assigning the tx, because this can lead to
* deadlock. Specifically, if this dnode is already
* assigned to an earlier txg, this thread may need
* to wait for that txg to sync (the ERESTART case
* below). The other thread that has assigned this
* dnode to an earlier txg prevents this txg from
* syncing until its tx can complete (calling
* dmu_tx_commit()), but it may need to acquire the
* dn_struct_rwlock to do so (e.g. via
* dmu_buf_hold*()).
*
* Note that this thread can't hold the lock for
* read either, but the rwlock doesn't record
* enough information to make that assertion.
*/
ASSERT(!RW_WRITE_HELD(&dn->dn_struct_rwlock));
mutex_enter(&dn->dn_mtx);
if (dn->dn_assigned_txg == tx->tx_txg - 1) {
mutex_exit(&dn->dn_mtx);
tx->tx_needassign_txh = txh;
DMU_TX_STAT_BUMP(dmu_tx_group);
return (SET_ERROR(ERESTART));
}
if (dn->dn_assigned_txg == 0)
dn->dn_assigned_txg = tx->tx_txg;
ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
(void) zfs_refcount_add(&dn->dn_tx_holds, tx);
mutex_exit(&dn->dn_mtx);
}
towrite += zfs_refcount_count(&txh->txh_space_towrite);
tohold += zfs_refcount_count(&txh->txh_memory_tohold);
}
/* needed allocation: worst-case estimate of write space */
uint64_t asize = spa_get_worst_case_asize(tx->tx_pool->dp_spa, towrite);
/* calculate memory footprint estimate */
uint64_t memory = towrite + tohold;
if (tx->tx_dir != NULL && asize != 0) {
int err = dsl_dir_tempreserve_space(tx->tx_dir, memory,
asize, tx->tx_netfree, &tx->tx_tempreserve_cookie, tx);
if (err != 0)
return (err);
}
DMU_TX_STAT_BUMP(dmu_tx_assigned);
return (0);
}
static void
dmu_tx_unassign(dmu_tx_t *tx)
{
if (tx->tx_txg == 0)
return;
txg_rele_to_quiesce(&tx->tx_txgh);
/*
* Walk the transaction's hold list, removing the hold on the
* associated dnode, and notifying waiters if the refcount drops to 0.
*/
for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds);
txh && txh != tx->tx_needassign_txh;
txh = list_next(&tx->tx_holds, txh)) {
dnode_t *dn = txh->txh_dnode;
if (dn == NULL)
continue;
mutex_enter(&dn->dn_mtx);
ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
if (zfs_refcount_remove(&dn->dn_tx_holds, tx) == 0) {
dn->dn_assigned_txg = 0;
cv_broadcast(&dn->dn_notxholds);
}
mutex_exit(&dn->dn_mtx);
}
txg_rele_to_sync(&tx->tx_txgh);
tx->tx_lasttried_txg = tx->tx_txg;
tx->tx_txg = 0;
}
/*
* Assign tx to a transaction group; txg_how is a bitmask:
*
* If TXG_WAIT is set and the currently open txg is full, this function
* will wait until there's a new txg. This should be used when no locks
* are being held. With this bit set, this function will only fail if
* we're truly out of space (or over quota).
*
* If TXG_WAIT is *not* set and we can't assign into the currently open
* txg without blocking, this function will return immediately with
* ERESTART. This should be used whenever locks are being held. On an
* ERESTART error, the caller should drop all locks, call dmu_tx_wait(),
* and try again.
*
* If TXG_NOTHROTTLE is set, this indicates that this tx should not be
* delayed due on the ZFS Write Throttle (see comments in dsl_pool.c for
* details on the throttle). This is used by the VFS operations, after
* they have already called dmu_tx_wait() (though most likely on a
* different tx).
*
* It is guaranteed that subsequent successful calls to dmu_tx_assign()
* will assign the tx to monotonically increasing txgs. Of course this is
* not strong monotonicity, because the same txg can be returned multiple
* times in a row. This guarantee holds both for subsequent calls from
* one thread and for multiple threads. For example, it is impossible to
* observe the following sequence of events:
*
* Thread 1 Thread 2
*
* dmu_tx_assign(T1, ...)
* 1 <- dmu_tx_get_txg(T1)
* dmu_tx_assign(T2, ...)
* 2 <- dmu_tx_get_txg(T2)
* dmu_tx_assign(T3, ...)
* 1 <- dmu_tx_get_txg(T3)
*/
int
dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how)
{
int err;
ASSERT(tx->tx_txg == 0);
ASSERT0(txg_how & ~(TXG_WAIT | TXG_NOTHROTTLE));
ASSERT(!dsl_pool_sync_context(tx->tx_pool));
/* If we might wait, we must not hold the config lock. */
IMPLY((txg_how & TXG_WAIT), !dsl_pool_config_held(tx->tx_pool));
if ((txg_how & TXG_NOTHROTTLE))
tx->tx_dirty_delayed = B_TRUE;
while ((err = dmu_tx_try_assign(tx, txg_how)) != 0) {
dmu_tx_unassign(tx);
if (err != ERESTART || !(txg_how & TXG_WAIT))
return (err);
dmu_tx_wait(tx);
}
txg_rele_to_quiesce(&tx->tx_txgh);
return (0);
}
void
dmu_tx_wait(dmu_tx_t *tx)
{
spa_t *spa = tx->tx_pool->dp_spa;
dsl_pool_t *dp = tx->tx_pool;
hrtime_t before;
ASSERT(tx->tx_txg == 0);
ASSERT(!dsl_pool_config_held(tx->tx_pool));
before = gethrtime();
if (tx->tx_wait_dirty) {
uint64_t dirty;
/*
* dmu_tx_try_assign() has determined that we need to wait
* because we've consumed much or all of the dirty buffer
* space.
*/
mutex_enter(&dp->dp_lock);
if (dp->dp_dirty_total >= zfs_dirty_data_max)
DMU_TX_STAT_BUMP(dmu_tx_dirty_over_max);
while (dp->dp_dirty_total >= zfs_dirty_data_max)
cv_wait(&dp->dp_spaceavail_cv, &dp->dp_lock);
dirty = dp->dp_dirty_total;
mutex_exit(&dp->dp_lock);
dmu_tx_delay(tx, dirty);
tx->tx_wait_dirty = B_FALSE;
/*
* Note: setting tx_dirty_delayed only has effect if the
* caller used TX_WAIT. Otherwise they are going to
* destroy this tx and try again. The common case,
* zfs_write(), uses TX_WAIT.
*/
tx->tx_dirty_delayed = B_TRUE;
} else if (spa_suspended(spa) || tx->tx_lasttried_txg == 0) {
/*
* If the pool is suspended we need to wait until it
* is resumed. Note that it's possible that the pool
* has become active after this thread has tried to
* obtain a tx. If that's the case then tx_lasttried_txg
* would not have been set.
*/
txg_wait_synced(dp, spa_last_synced_txg(spa) + 1);
} else if (tx->tx_needassign_txh) {
dnode_t *dn = tx->tx_needassign_txh->txh_dnode;
mutex_enter(&dn->dn_mtx);
while (dn->dn_assigned_txg == tx->tx_lasttried_txg - 1)
cv_wait(&dn->dn_notxholds, &dn->dn_mtx);
mutex_exit(&dn->dn_mtx);
tx->tx_needassign_txh = NULL;
} else {
/*
* If we have a lot of dirty data just wait until we sync
* out a TXG at which point we'll hopefully have synced
* a portion of the changes.
*/
txg_wait_synced(dp, spa_last_synced_txg(spa) + 1);
}
spa_tx_assign_add_nsecs(spa, gethrtime() - before);
}
static void
dmu_tx_destroy(dmu_tx_t *tx)
{
dmu_tx_hold_t *txh;
while ((txh = list_head(&tx->tx_holds)) != NULL) {
dnode_t *dn = txh->txh_dnode;
list_remove(&tx->tx_holds, txh);
zfs_refcount_destroy_many(&txh->txh_space_towrite,
zfs_refcount_count(&txh->txh_space_towrite));
zfs_refcount_destroy_many(&txh->txh_memory_tohold,
zfs_refcount_count(&txh->txh_memory_tohold));
kmem_free(txh, sizeof (dmu_tx_hold_t));
if (dn != NULL)
dnode_rele(dn, tx);
}
list_destroy(&tx->tx_callbacks);
list_destroy(&tx->tx_holds);
kmem_free(tx, sizeof (dmu_tx_t));
}
void
dmu_tx_commit(dmu_tx_t *tx)
{
ASSERT(tx->tx_txg != 0);
/*
* Go through the transaction's hold list and remove holds on
* associated dnodes, notifying waiters if no holds remain.
*/
for (dmu_tx_hold_t *txh = list_head(&tx->tx_holds); txh != NULL;
txh = list_next(&tx->tx_holds, txh)) {
dnode_t *dn = txh->txh_dnode;
if (dn == NULL)
continue;
mutex_enter(&dn->dn_mtx);
ASSERT3U(dn->dn_assigned_txg, ==, tx->tx_txg);
if (zfs_refcount_remove(&dn->dn_tx_holds, tx) == 0) {
dn->dn_assigned_txg = 0;
cv_broadcast(&dn->dn_notxholds);
}
mutex_exit(&dn->dn_mtx);
}
if (tx->tx_tempreserve_cookie)
dsl_dir_tempreserve_clear(tx->tx_tempreserve_cookie, tx);
if (!list_is_empty(&tx->tx_callbacks))
txg_register_callbacks(&tx->tx_txgh, &tx->tx_callbacks);
if (tx->tx_anyobj == FALSE)
txg_rele_to_sync(&tx->tx_txgh);
dmu_tx_destroy(tx);
}
void
dmu_tx_abort(dmu_tx_t *tx)
{
ASSERT(tx->tx_txg == 0);
/*
* Call any registered callbacks with an error code.
*/
if (!list_is_empty(&tx->tx_callbacks))
dmu_tx_do_callbacks(&tx->tx_callbacks, SET_ERROR(ECANCELED));
dmu_tx_destroy(tx);
}
uint64_t
dmu_tx_get_txg(dmu_tx_t *tx)
{
ASSERT(tx->tx_txg != 0);
return (tx->tx_txg);
}
dsl_pool_t *
dmu_tx_pool(dmu_tx_t *tx)
{
ASSERT(tx->tx_pool != NULL);
return (tx->tx_pool);
}
void
dmu_tx_callback_register(dmu_tx_t *tx, dmu_tx_callback_func_t *func, void *data)
{
dmu_tx_callback_t *dcb;
dcb = kmem_alloc(sizeof (dmu_tx_callback_t), KM_SLEEP);
dcb->dcb_func = func;
dcb->dcb_data = data;
list_insert_tail(&tx->tx_callbacks, dcb);
}
/*
* Call all the commit callbacks on a list, with a given error code.
*/
void
dmu_tx_do_callbacks(list_t *cb_list, int error)
{
dmu_tx_callback_t *dcb;
while ((dcb = list_tail(cb_list)) != NULL) {
list_remove(cb_list, dcb);
dcb->dcb_func(dcb->dcb_data, error);
kmem_free(dcb, sizeof (dmu_tx_callback_t));
}
}
/*
* Interface to hold a bunch of attributes.
* used for creating new files.
* attrsize is the total size of all attributes
* to be added during object creation
*
* For updating/adding a single attribute dmu_tx_hold_sa() should be used.
*/
/*
* hold necessary attribute name for attribute registration.
* should be a very rare case where this is needed. If it does
* happen it would only happen on the first write to the file system.
*/
static void
dmu_tx_sa_registration_hold(sa_os_t *sa, dmu_tx_t *tx)
{
if (!sa->sa_need_attr_registration)
return;
for (int i = 0; i != sa->sa_num_attrs; i++) {
if (!sa->sa_attr_table[i].sa_registered) {
if (sa->sa_reg_attr_obj)
dmu_tx_hold_zap(tx, sa->sa_reg_attr_obj,
B_TRUE, sa->sa_attr_table[i].sa_name);
else
dmu_tx_hold_zap(tx, DMU_NEW_OBJECT,
B_TRUE, sa->sa_attr_table[i].sa_name);
}
}
}
void
dmu_tx_hold_spill(dmu_tx_t *tx, uint64_t object)
{
dmu_tx_hold_t *txh;
txh = dmu_tx_hold_object_impl(tx, tx->tx_objset, object,
THT_SPILL, 0, 0);
if (txh != NULL)
(void) zfs_refcount_add_many(&txh->txh_space_towrite,
SPA_OLD_MAXBLOCKSIZE, FTAG);
}
void
dmu_tx_hold_sa_create(dmu_tx_t *tx, int attrsize)
{
sa_os_t *sa = tx->tx_objset->os_sa;
dmu_tx_hold_bonus(tx, DMU_NEW_OBJECT);
if (tx->tx_objset->os_sa->sa_master_obj == 0)
return;
if (tx->tx_objset->os_sa->sa_layout_attr_obj) {
dmu_tx_hold_zap(tx, sa->sa_layout_attr_obj, B_TRUE, NULL);
} else {
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_LAYOUTS);
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
}
dmu_tx_sa_registration_hold(sa, tx);
if (attrsize <= DN_OLD_MAX_BONUSLEN && !sa->sa_force_spill)
return;
(void) dmu_tx_hold_object_impl(tx, tx->tx_objset, DMU_NEW_OBJECT,
THT_SPILL, 0, 0);
}
/*
* Hold SA attribute
*
* dmu_tx_hold_sa(dmu_tx_t *tx, sa_handle_t *, attribute, add, size)
*
* variable_size is the total size of all variable sized attributes
* passed to this function. It is not the total size of all
* variable size attributes that *may* exist on this object.
*/
void
dmu_tx_hold_sa(dmu_tx_t *tx, sa_handle_t *hdl, boolean_t may_grow)
{
uint64_t object;
sa_os_t *sa = tx->tx_objset->os_sa;
ASSERT(hdl != NULL);
object = sa_handle_object(hdl);
dmu_buf_impl_t *db = (dmu_buf_impl_t *)hdl->sa_bonus;
DB_DNODE_ENTER(db);
dmu_tx_hold_bonus_by_dnode(tx, DB_DNODE(db));
DB_DNODE_EXIT(db);
if (tx->tx_objset->os_sa->sa_master_obj == 0)
return;
if (tx->tx_objset->os_sa->sa_reg_attr_obj == 0 ||
tx->tx_objset->os_sa->sa_layout_attr_obj == 0) {
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_LAYOUTS);
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, B_TRUE, NULL);
}
dmu_tx_sa_registration_hold(sa, tx);
if (may_grow && tx->tx_objset->os_sa->sa_layout_attr_obj)
dmu_tx_hold_zap(tx, sa->sa_layout_attr_obj, B_TRUE, NULL);
if (sa->sa_force_spill || may_grow || hdl->sa_spill) {
ASSERT(tx->tx_txg == 0);
dmu_tx_hold_spill(tx, object);
} else {
dnode_t *dn;
DB_DNODE_ENTER(db);
dn = DB_DNODE(db);
if (dn->dn_have_spill) {
ASSERT(tx->tx_txg == 0);
dmu_tx_hold_spill(tx, object);
}
DB_DNODE_EXIT(db);
}
}
void
dmu_tx_init(void)
{
dmu_tx_ksp = kstat_create("zfs", 0, "dmu_tx", "misc",
KSTAT_TYPE_NAMED, sizeof (dmu_tx_stats) / sizeof (kstat_named_t),
KSTAT_FLAG_VIRTUAL);
if (dmu_tx_ksp != NULL) {
dmu_tx_ksp->ks_data = &dmu_tx_stats;
kstat_install(dmu_tx_ksp);
}
}
void
dmu_tx_fini(void)
{
if (dmu_tx_ksp != NULL) {
kstat_delete(dmu_tx_ksp);
dmu_tx_ksp = NULL;
}
}
#if defined(_KERNEL)
EXPORT_SYMBOL(dmu_tx_create);
EXPORT_SYMBOL(dmu_tx_hold_write);
EXPORT_SYMBOL(dmu_tx_hold_write_by_dnode);
EXPORT_SYMBOL(dmu_tx_hold_free);
EXPORT_SYMBOL(dmu_tx_hold_free_by_dnode);
EXPORT_SYMBOL(dmu_tx_hold_zap);
EXPORT_SYMBOL(dmu_tx_hold_zap_by_dnode);
EXPORT_SYMBOL(dmu_tx_hold_bonus);
EXPORT_SYMBOL(dmu_tx_hold_bonus_by_dnode);
EXPORT_SYMBOL(dmu_tx_abort);
EXPORT_SYMBOL(dmu_tx_assign);
EXPORT_SYMBOL(dmu_tx_wait);
EXPORT_SYMBOL(dmu_tx_commit);
EXPORT_SYMBOL(dmu_tx_mark_netfree);
EXPORT_SYMBOL(dmu_tx_get_txg);
EXPORT_SYMBOL(dmu_tx_callback_register);
EXPORT_SYMBOL(dmu_tx_do_callbacks);
EXPORT_SYMBOL(dmu_tx_hold_spill);
EXPORT_SYMBOL(dmu_tx_hold_sa_create);
EXPORT_SYMBOL(dmu_tx_hold_sa);
#endif
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