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mirror_zfs/module/zfs/dmu_tx.c
Matthew Ahrens 6c9882d5db Improve performance by using dmu_tx_hold_*_by_dnode() 
In zfs_write() and dmu_tx_hold_sa(), we can use dmu_tx_hold_*_by_dnode()
instead of dmu_tx_hold_*(), since we already have a dbuf from the target
dnode in hand.  This eliminates some calls to dnode_hold(), which can be
expensive.  This is especially impactful if several threads are
accessing objects that are in the same block of dnodes, because they
will contend for that dbuf's lock.

We are seeing 10-20% performance wins for the sequential_writes tests in
the performance test suite, when doing >=128K writes to files with
recordsize=8K.

This also removes some unnecessary casts that are in the area.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #9081
2019-09-25 11:27:50 -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 (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_dmu.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_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));
err = dbuf_read(db, zio, DB_RF_CANFAIL | DB_RF_NOPREFETCH);
dbuf_rele(db, FTAG);
return (err);
}
/* ARGSUSED */
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 (zfs_refcount_count(&txh->txh_space_towrite) > 2 * DMU_MAX_ACCESS)
err = SET_ERROR(EFBIG);
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_remap_l1indirect(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_WRITE, 0, 0);
if (txh == NULL)
return;
dnode_t *dn = txh->txh_dnode;
(void) zfs_refcount_add_many(&txh->txh_space_towrite,
1ULL << dn->dn_indblkshift, FTAG);
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;
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,
MZAP_MAX_BLKSZ, 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, beginblk, 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.
*/
hrtime_t zfs_delay_max_ns = 100 * MICROSEC; /* 100 milliseconds */
int zfs_delay_resolution_ns = 100 * 1000; /* 100 microseconds */
/*
* 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 =
zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
hrtime_t wakeup, min_tx_time, now;
if (dirty <= delay_min_bytes)
return;
/*
* 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);
now = gethrtime();
min_tx_time = zfs_delay_scale *
(dirty - delay_min_bytes) / (zfs_dirty_data_max - dirty);
min_tx_time = MIN(min_tx_time, zfs_delay_max_ns);
if (now > tx->tx_start + min_tx_time)
return;
DTRACE_PROBE3(delay__mintime, dmu_tx_t *, tx, uint64_t, dirty,
uint64_t, min_tx_time);
mutex_enter(&dp->dp_lock);
wakeup = MAX(tx->tx_start + min_tx_time,
dp->dp_last_wakeup + min_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_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).
*/
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, 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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