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Remove duplicate dbufs accounting 

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
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 9 additions and 4 deletions
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7
include/sys/dnode.h
View File

@ -372,6 +372,13 @@ struct dnode {
struct zfetch dn_zfetch;
};
/*
* Since AVL already has embedded element counter, use dn_dbufs_count
* only for dbufs not counted there (bonus buffers) and just add them.
*/
#define DN_DBUFS_COUNT(dn) ((dn)->dn_dbufs_count + \
avl_numnodes(&(dn)->dn_dbufs))
/*
* We use this (otherwise unused) bit to indicate if the value of
* dn_next_maxblkid[txgoff] is valid to use in dnode_sync().

2
module/zfs/dbuf.c
View File

@ -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);

4
module/zfs/dnode.c
View File

@ -1004,7 +1004,7 @@ dnode_move(void *buf, void *newbuf, size_t size, void *arg)
*/
refcount = zfs_refcount_count(&odn->dn_holds);
ASSERT(refcount >= 0);
dbufs = odn->dn_dbufs_count;
dbufs = DN_DBUFS_COUNT(odn);
/* We can't have more dbufs than dnode holds. */
ASSERT3U(dbufs, <=, refcount);
@ -1031,7 +1031,7 @@ dnode_move(void *buf, void *newbuf, size_t size, void *arg)
list_link_replace(&odn->dn_link, &ndn->dn_link);
/* If the dnode was safe to move, the refcount cannot have changed. */
ASSERT(refcount == zfs_refcount_count(&ndn->dn_holds));
ASSERT(dbufs == ndn->dn_dbufs_count);
ASSERT(dbufs == DN_DBUFS_COUNT(ndn));
zrl_exit(&ndn->dn_handle->dnh_zrlock); /* handle has moved */
mutex_exit(&os->os_lock);