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Avoid unneccessary zio allocation and wait 

In function dmu_buf_hold_array_by_dnode, the usage of zio is only for 
the reading operation. Only create the zio and wait it in the reading 
scenario as a performance optimization.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Finix Yan <yancw@info2soft.com>
Closes #11251 
Closes #11256
This commit is contained in:
Finix1979 2020-12-03 01:28:55 +08:00 committed by GitHub
parent 95a78a035a
commit ec50cd24ba
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 14 additions and 11 deletions
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11
module/zfs/dmu.c
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@ -499,7 +499,7 @@ dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
uint64_t blkid, nblks, i;
uint32_t dbuf_flags;
int err;
zio_t *zio;
zio_t *zio = NULL;
ASSERT(length <= DMU_MAX_ACCESS);
@ -531,13 +531,16 @@ dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
}
dbp = kmem_zalloc(sizeof (dmu_buf_t *) * nblks, KM_SLEEP);
zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, ZIO_FLAG_CANFAIL);
if (read)
zio = zio_root(dn->dn_objset->os_spa, NULL, NULL,
ZIO_FLAG_CANFAIL);
blkid = dbuf_whichblock(dn, 0, offset);
for (i = 0; i < nblks; i++) {
dmu_buf_impl_t *db = dbuf_hold(dn, blkid + i, tag);
if (db == NULL) {
rw_exit(&dn->dn_struct_rwlock);
dmu_buf_rele_array(dbp, nblks, tag);
if (read)
zio_nowait(zio);
return (SET_ERROR(EIO));
}
@ -555,7 +558,8 @@ dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
}
rw_exit(&dn->dn_struct_rwlock);
/* wait for async i/o */
if (read) {
/* wait for async read i/o */
err = zio_wait(zio);
if (err) {
dmu_buf_rele_array(dbp, nblks, tag);
@ -563,7 +567,6 @@ dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
}
/* wait for other io to complete */
if (read) {
for (i = 0; i < nblks; i++) {
dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbp[i];
mutex_enter(&db->db_mtx);