[src/trunk]: src/sys/kern Update comment on vnode life-cycle a little.

[rmind <rmind%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/67f7a44f47b4
branches:  trunk
changeset: 782009:67f7a44f47b4
user:      rmind <rmind%NetBSD.org@localhost>
date:      Fri Oct 12 21:10:55 2012 +0000

description:
Update comment on vnode life-cycle a little.

diffstat:

 sys/kern/vfs_vnode.c |  23 ++++++++++++++++-------
 1 files changed, 16 insertions(+), 7 deletions(-)

diffs (63 lines):

diff -r 7255b8739163 -r 67f7a44f47b4 sys/kern/vfs_vnode.c
--- a/sys/kern/vfs_vnode.c      Fri Oct 12 20:27:39 2012 +0000
+++ b/sys/kern/vfs_vnode.c      Fri Oct 12 21:10:55 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnode.c,v 1.15 2011/12/20 16:49:37 hannken Exp $   */
+/*     $NetBSD: vfs_vnode.c,v 1.16 2012/10/12 21:10:55 rmind Exp $     */
 
 /*-
  * Copyright (c) 1997-2011 The NetBSD Foundation, Inc.
@@ -78,11 +78,15 @@
  *     - Allocation, via getnewvnode(9) and/or vnalloc(9).
  *     - Reclamation of inactive vnode, via vget(9).
  *
+ *     Recycle from a free list, via getnewvnode(9) -> getcleanvnode(9)
+ *     was another, traditional way.  Currently, only the draining thread
+ *     recycles the vnodes.  This behaviour might be revisited.
+ *
  *     The life-cycle ends when the last reference is dropped, usually
  *     in VOP_REMOVE(9).  In such case, VOP_INACTIVE(9) is called to inform
  *     the file system that vnode is inactive.  Via this call, file system
- *     indicates whether vnode should be recycled (usually, count of links
- *     is checked i.e. whether file was removed).
+ *     indicates whether vnode can be recycled (usually, it checks its own
+ *     references, e.g. count of links, whether the file was removed).
  *
  *     Depending on indication, vnode can be put into a free list (cache),
  *     or cleaned via vclean(9), which calls VOP_RECLAIM(9) to disassociate
@@ -120,7 +124,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.15 2011/12/20 16:49:37 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.16 2012/10/12 21:10:55 rmind Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -147,18 +151,23 @@
 u_int                  numvnodes               __cacheline_aligned;
 
 static pool_cache_t    vnode_cache             __read_mostly;
+
+/*
+ * There are two free lists: one is for vnodes which have no buffer/page
+ * references and one for those which do (i.e. v_holdcnt is non-zero).
+ * Vnode recycling mechanism first attempts to look into the former list.
+ */
 static kmutex_t                vnode_free_list_lock    __cacheline_aligned;
-
 static vnodelst_t      vnode_free_list         __cacheline_aligned;
 static vnodelst_t      vnode_hold_list         __cacheline_aligned;
+static kcondvar_t      vdrain_cv               __cacheline_aligned;
+
 static vnodelst_t      vrele_list              __cacheline_aligned;
-
 static kmutex_t                vrele_lock              __cacheline_aligned;
 static kcondvar_t      vrele_cv                __cacheline_aligned;
 static lwp_t *         vrele_lwp               __cacheline_aligned;
 static int             vrele_pending           __cacheline_aligned;
 static int             vrele_gen               __cacheline_aligned;
-static kcondvar_t      vdrain_cv               __cacheline_aligned;
 
 static int             cleanvnode(void);
 static void            vdrain_thread(void *);