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Use rw_tryupgrade() in dmu_bonus_hold_by_dnode()

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When dn->dn_bonus == NULL, dmu_bonus_hold_by_dnode() will unlock its
read lock on dn->dn_struct_rwlock and grab a write lock. This can be
micro-optimized by calling rw_tryupgrade().

Linux will not benefit from this since it does not support rwlock
upgrades, but FreeBSD will.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14517
This commit is contained in:
Richard Yao 2023-02-22 19:33:23 -05:00 committed by GitHub
parent d9e64a4030
commit c9e39da9a4
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 4 additions and 2 deletions
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6
module/zfs/dmu.c
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@ -357,8 +357,10 @@ int dmu_bonus_hold_by_dnode(dnode_t *dn, const void *tag, dmu_buf_t **dbp,
rw_enter(&dn->dn_struct_rwlock, RW_READER);
if (dn->dn_bonus == NULL) {
rw_exit(&dn->dn_struct_rwlock);
rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
if (!rw_tryupgrade(&dn->dn_struct_rwlock)) {
rw_exit(&dn->dn_struct_rwlock);
rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
}
if (dn->dn_bonus == NULL)
dbuf_create_bonus(dn);
}