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Date:      Fri, 21 Feb 2020 04:33:14 +0000 (UTC)
From:      Alexander Motin <mav@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org
Subject:   svn commit: r358204 - in stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs: . sys
Message-ID:  <202002210433.01L4XELo068570@repo.freebsd.org>
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Author: mav
Date: Fri Feb 21 04:33:14 2020
New Revision: 358204
URL: https://svnweb.freebsd.org/changeset/base/358204

Log:
  MFC r357657: 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.
  
  This counter is used only on illumos, so for FreeBSD it was just a
  waste of time.

Modified:
  stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
  stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
  stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dnode.h
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
==============================================================================
--- stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c	Fri Feb 21 04:31:30 2020	(r358203)
+++ stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c	Fri Feb 21 04:33:14 2020	(r358204)
@@ -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);
 

Modified: stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
==============================================================================
--- stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c	Fri Feb 21 04:31:30 2020	(r358203)
+++ stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c	Fri Feb 21 04:33:14 2020	(r358204)
@@ -998,7 +998,7 @@ dnode_move(void *buf, void *newbuf, size_t size, void 
 	 */
 	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 
 	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);
 

Modified: stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dnode.h
==============================================================================
--- stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dnode.h	Fri Feb 21 04:31:30 2020	(r358203)
+++ stable/12/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dnode.h	Fri Feb 21 04:33:14 2020	(r358204)
@@ -346,6 +346,13 @@ struct dnode {
 };
 
 /*
+ * 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
  * individually, but as an array of child dnodes in dnode_hold_impl().

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