svn commit: r365786 - head/sys/fs/tmpfs

[Konstantin Belousov]

Author: kib
Date: Tue Sep 15 22:13:21 2020
New Revision: 365786
URL: https://svnweb.freebsd.org/changeset/base/365786

Log:
  Microoptimize tmpfs node ref/unref by using atomics.
  
  Avoid tmpfs mount and node locks when ref count is greater than zero,
  which is the case until node is being destroyed by unlink or unmount.
  
  Reviewed by:	markj
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  Differential revision:	https://reviews.freebsd.org/D26346

Modified:
  head/sys/fs/tmpfs/tmpfs.h
  head/sys/fs/tmpfs/tmpfs_subr.c
  head/sys/fs/tmpfs/tmpfs_vnops.c

Modified: head/sys/fs/tmpfs/tmpfs.h
==============================================================================
--- head/sys/fs/tmpfs/tmpfs.h	Tue Sep 15 22:06:36 2020	(r365785)
+++ head/sys/fs/tmpfs/tmpfs.h	Tue Sep 15 22:13:21 2020	(r365786)
@@ -228,7 +228,7 @@ struct tmpfs_node {
 	int		tn_vpstate;		/* (i) */
 
 	/* Transient refcounter on this node. */
-	u_int		tn_refcount;		/* (m) + (i) */
+	u_int		tn_refcount;		/* 0<->1 (m) + (i) */
 
 	/* misc data field for different tn_type node */
 	union {
@@ -412,7 +412,6 @@ struct tmpfs_dir_cursor {
  */
 
 void	tmpfs_ref_node(struct tmpfs_node *node);
-void	tmpfs_ref_node_locked(struct tmpfs_node *node);
 int	tmpfs_alloc_node(struct mount *mp, struct tmpfs_mount *, enum vtype,
 	    uid_t uid, gid_t gid, mode_t mode, struct tmpfs_node *,
 	    const char *, dev_t, struct tmpfs_node **);

Modified: head/sys/fs/tmpfs/tmpfs_subr.c
==============================================================================
--- head/sys/fs/tmpfs/tmpfs_subr.c	Tue Sep 15 22:06:36 2020	(r365785)
+++ head/sys/fs/tmpfs/tmpfs_subr.c	Tue Sep 15 22:13:21 2020	(r365786)
@@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/priv.h>
 #include <sys/proc.h>
 #include <sys/random.h>
+#include <sys/refcount.h>
 #include <sys/rwlock.h>
 #include <sys/stat.h>
 #include <sys/sysctl.h>
@@ -211,23 +212,17 @@ tmpfs_pages_check_avail(struct tmpfs_mount *tmp, size_
 void
 tmpfs_ref_node(struct tmpfs_node *node)
 {
+#ifdef INVARIANTS
+	u_int old;
 
-	TMPFS_NODE_LOCK(node);
-	tmpfs_ref_node_locked(node);
-	TMPFS_NODE_UNLOCK(node);
+	old =
+#endif
+	refcount_acquire(&node->tn_refcount);
+#ifdef INVARIANTS
+	KASSERT(old > 0, ("node %p zero refcount", node));
+#endif
 }
 
-void
-tmpfs_ref_node_locked(struct tmpfs_node *node)
-{
-
-	TMPFS_NODE_ASSERT_LOCKED(node);
-	KASSERT(node->tn_refcount > 0, ("node %p zero refcount", node));
-	KASSERT(node->tn_refcount < UINT_MAX, ("node %p refcount %u", node,
-	    node->tn_refcount));
-	node->tn_refcount++;
-}
-
 /*
  * Allocates a new node of type 'type' inside the 'tmp' mount point, with
  * its owner set to 'uid', its group to 'gid' and its mode set to 'mode',
@@ -370,6 +365,8 @@ tmpfs_alloc_node(struct mount *mp, struct tmpfs_mount 
 void
 tmpfs_free_node(struct tmpfs_mount *tmp, struct tmpfs_node *node)
 {
+	if (refcount_release_if_not_last(&node->tn_refcount))
+		return;
 
 	TMPFS_LOCK(tmp);
 	TMPFS_NODE_LOCK(node);
@@ -384,19 +381,19 @@ tmpfs_free_node_locked(struct tmpfs_mount *tmp, struct
     bool detach)
 {
 	vm_object_t uobj;
+	bool last;
 
 	TMPFS_MP_ASSERT_LOCKED(tmp);
 	TMPFS_NODE_ASSERT_LOCKED(node);
-	KASSERT(node->tn_refcount > 0, ("node %p refcount zero", node));
 
-	node->tn_refcount--;
-	if (node->tn_attached && (detach || node->tn_refcount == 0)) {
+	last = refcount_release(&node->tn_refcount);
+	if (node->tn_attached && (detach || last)) {
 		MPASS(tmp->tm_nodes_inuse > 0);
 		tmp->tm_nodes_inuse--;
 		LIST_REMOVE(node, tn_entries);
 		node->tn_attached = false;
 	}
-	if (node->tn_refcount > 0)
+	if (!last)
 		return (false);
 
 #ifdef INVARIANTS
@@ -596,7 +593,7 @@ tmpfs_alloc_vp(struct mount *mp, struct tmpfs_node *no
 	error = 0;
 	tm = VFS_TO_TMPFS(mp);
 	TMPFS_NODE_LOCK(node);
-	tmpfs_ref_node_locked(node);
+	tmpfs_ref_node(node);
 loop:
 	TMPFS_NODE_ASSERT_LOCKED(node);
 	if ((vp = node->tn_vnode) != NULL) {

Modified: head/sys/fs/tmpfs/tmpfs_vnops.c
==============================================================================
--- head/sys/fs/tmpfs/tmpfs_vnops.c	Tue Sep 15 22:06:36 2020	(r365785)
+++ head/sys/fs/tmpfs/tmpfs_vnops.c	Tue Sep 15 22:13:21 2020	(r365786)
@@ -1663,7 +1663,7 @@ restart:
 		if (tnp->tn_type != VDIR)
 			continue;
 		TMPFS_NODE_LOCK(tnp);
-		tmpfs_ref_node_locked(tnp);
+		tmpfs_ref_node(tnp);
 
 		/*
 		 * tn_vnode cannot be instantiated while we hold the