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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.

This counter is used only on illumos, so for FreeBSD it was just a
waste of time.

MFC after:	2 weeks
This commit is contained in:
Alexander Motin 2020-02-07 15:50:47 +00:00
parent a1b769b32d
commit 8d8e484d9c
3 changed files with 9 additions and 4 deletions
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2
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
View File

@ -2375,7 +2375,6 @@ dbuf_destroy(dmu_buf_impl_t *db)
if (needlock)
mutex_enter(&dn->dn_dbufs_mtx);
avl_remove(&dn->dn_dbufs, db);
atomic_dec_32(&dn->dn_dbufs_count);
membar_producer();
DB_DNODE_EXIT(db);
if (needlock)
@ -2600,7 +2599,6 @@ 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
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
View File

@ -998,7 +998,7 @@ 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);
@ -1025,7 +1025,7 @@ 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);

7
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dnode.h
View File

@ -345,6 +345,13 @@ 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))
/*
* Adds a level of indirection between the dbuf and the dnode to avoid
* iterating descendent dbufs in dnode_move(). Handles are not allocated