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Remove duplicate dbufs accounting

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Since AVL already has embedded element counter, use dn_dbufs_count
only for dbufs not counted there (bonus buffers) and just add them.
This removes two atomics per dbuf life cycle.

According to profiler it reduces time spent by dbuf_destroy() inside
bottlenecked dbuf_evict_thread() from 13.36% to 9.20% of the core.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #9949
This commit is contained in:
Alexander Motin
2020-02-13 14:20:42 -05:00
committed by GitHub
parent 610eec452d
commit 465e4e795e
3 changed files with 9 additions and 4 deletions
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module/zfs/dbuf.c
-2
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@@ -2688,7 +2688,6 @@ dbuf_destroy(dmu_buf_impl_t *db)
mutex_enter_nested(&dn->dn_dbufs_mtx,
NESTED_SINGLE);
avl_remove(&dn->dn_dbufs, db);
atomic_dec_32(&dn->dn_dbufs_count);
membar_producer();
DB_DNODE_EXIT(db);
if (needlock)
@@ -2912,7 +2911,6 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
zfs_refcount_count(&dn->dn_holds) > 0);
(void) zfs_refcount_add(&dn->dn_holds, db);
atomic_inc_32(&dn->dn_dbufs_count);
dprintf_dbuf(db, "db=%p\n", db);