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ZIL: Avoid dbuf_read() before dmu_sync().

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In most cases dmu_sync() works with dirty records directly and does
not need actual data. The only exception is dmu_sync_late_arrival().
To save some CPU time use dmu_buf_hold_noread*() in z*_get_data()
and explicitly call dbuf_read() in dmu_sync_late_arrival(). There
is also a chance that by that time TXG will already be synced and
we won't have to do it at all.

Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15153
This commit is contained in:
Alexander Motin
2023-08-11 12:04:08 -04:00
committed by GitHub
parent 8ce2eba9e6
commit bdb7df4245
5 changed files with 16 additions and 7 deletions
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module/zfs/dmu.c
+8 -1
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@@ -165,7 +165,7 @@ dmu_object_byteswap_info_t dmu_ot_byteswap[DMU_BSWAP_NUMFUNCS] = {
{ zfs_acl_byteswap, "acl" }
};
static int
int
dmu_buf_hold_noread_by_dnode(dnode_t *dn, uint64_t offset,
const void *tag, dmu_buf_t **dbp)
{
@@ -185,6 +185,7 @@ dmu_buf_hold_noread_by_dnode(dnode_t *dn, uint64_t offset,
*dbp = &db->db;
return (0);
}
int
dmu_buf_hold_noread(objset_t *os, uint64_t object, uint64_t offset,
const void *tag, dmu_buf_t **dbp)
@@ -1672,6 +1673,12 @@ dmu_sync_late_arrival(zio_t *pio, objset_t *os, dmu_sync_cb_t *done, zgd_t *zgd,
{
dmu_sync_arg_t *dsa;
dmu_tx_t *tx;
int error;
error = dbuf_read((dmu_buf_impl_t *)zgd->zgd_db, NULL,
DB_RF_CANFAIL | DB_RF_NOPREFETCH);
if (error != 0)
return (error);
tx = dmu_tx_create(os);
dmu_tx_hold_space(tx, zgd->zgd_db->db_size);