[src/trunk]: src/sys/kern - Stats: add a cast to make sure 32-bit wraparound ...

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

details:   https://anonhg.NetBSD.org/src/rev/969113c86ff2
branches:  trunk
changeset: 1008568:969113c86ff2
user:      ad <ad%NetBSD.org@localhost>
date:      Fri Mar 27 00:14:25 2020 +0000

description:
- Stats: add a cast to make sure 32-bit wraparound works properly.
- cache_purge_children(): just use RB_TREE_MIN().
- Change the name of the pool to "namecache".
- Update comments.

diffstat:

 sys/kern/vfs_cache.c |  39 ++++++++++++++++++++-------------------
 1 files changed, 20 insertions(+), 19 deletions(-)

diffs (115 lines):

diff -r bfe5a3825c75 -r 969113c86ff2 sys/kern/vfs_cache.c
--- a/sys/kern/vfs_cache.c      Fri Mar 27 00:13:52 2020 +0000
+++ b/sys/kern/vfs_cache.c      Fri Mar 27 00:14:25 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_cache.c,v 1.134 2020/03/23 20:02:13 ad Exp $       */
+/*     $NetBSD: vfs_cache.c,v 1.135 2020/03/27 00:14:25 ad Exp $       */
 
 /*-
  * Copyright (c) 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -172,7 +172,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.134 2020/03/23 20:02:13 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.135 2020/03/27 00:14:25 ad Exp $");
 
 #define __NAMECACHE_PRIVATE
 #ifdef _KERNEL_OPT
@@ -250,7 +250,7 @@
 
 #define        UPDATE(nchcpu, f) do { \
        uint32_t cur = atomic_load_relaxed(&nchcpu->cur.f); \
-       nchstats.f += cur - nchcpu->last.f; \
+       nchstats.f += (uint32_t)(cur - nchcpu->last.f); \
        nchcpu->last.f = cur; \
 } while (/* CONSTCOND */ 0)
 
@@ -409,9 +409,9 @@
         * tailored for exactly what's needed here (64-bit key and so on)
         * that is quite a bit faster than using rb_tree_find_node(). 
         *
-        * In the fast path memcmp() needs to be called at least once to
-        * confirm that the correct name has been found.  If there has been
-        * a hash value collision (very rare) the search will continue on.
+        * For a matching key memcmp() needs to be called once to confirm
+        * that the correct name has been found.  Very rarely there will be
+        * a key value collision and the search will continue.
         */
        for (;;) {
                if (__predict_false(RB_SENTINEL_P(node))) {
@@ -791,7 +791,10 @@
                        }
                }
 
-               /* Record a hit on the entry.  This is an unlocked read. */
+               /*
+                * Record a hit on the entry.  This is an unlocked read but
+                * even if wrong it doesn't matter too much.
+                */
                lrulist = atomic_load_relaxed(&ncp->nc_lrulist);
                if (lrulist != LRU_ACTIVE) {
                        cache_activate(ncp);
@@ -905,8 +908,8 @@
 
        /*
         * With the directory lock still held, insert to the tail of the
-        * ACTIVE LRU list (new) and with the LRU lock held take the to
-        * opportunity to incrementally balance the lists.
+        * ACTIVE LRU list (new) and take the opportunity to incrementally
+        * balance the lists.
         */
        mutex_enter(&cache_lru_lock);
        ncp->nc_lrulist = LRU_ACTIVE;
@@ -916,8 +919,10 @@
        mutex_exit(&cache_lru_lock);
 
        /*
-        * Finally, insert to the vnode, and unlock.  Partially sort the
-        * per-vnode list: dots go to back.
+        * Finally, insert to the vnode and unlock.  With everything set up
+        * it's safe to let cache_revlookup() see the entry.  Partially sort
+        * the per-vnode list: dots go to back so cache_revlookup() doesn't
+        * have to consider them.
         */
        if (vp != NULL) {
                vnode_impl_t *vi = VNODE_TO_VIMPL(vp);
@@ -987,7 +992,7 @@
 {
 
        cache_pool = pool_cache_init(sizeof(struct namecache),
-           coherency_unit, 0, 0, "nchentry", NULL, IPL_NONE, NULL,
+           coherency_unit, 0, 0, "namecache", NULL, IPL_NONE, NULL,
            NULL, NULL);
        KASSERT(cache_pool != NULL);
 
@@ -1126,11 +1131,7 @@
        SDT_PROBE(vfs, namecache, purge, children, dvp, 0, 0, 0, 0);
 
        rw_enter(&dvi->vi_nc_lock, RW_WRITER);
-       for (;;) {
-               ncp = rb_tree_iterate(&dvi->vi_nc_tree, NULL, RB_DIR_RIGHT);
-               if (ncp == NULL) {
-                       break;
-               }
+       while ((ncp = RB_TREE_MIN(&dvi->vi_nc_tree)) != NULL) {
                cache_remove(ncp, true);
        }
        rw_exit(&dvi->vi_nc_lock);
@@ -1210,14 +1211,14 @@
 }
 
 /*
- * Re-queue an entry onto the correct LRU list, after it has scored a hit.
+ * Re-queue an entry onto the tail of the active LRU list, after it has
+ * scored a hit.
  */
 static void
 cache_activate(struct namecache *ncp)
 {
 
        mutex_enter(&cache_lru_lock);
-       /* Put on tail of ACTIVE list, since it just scored a hit. */
        TAILQ_REMOVE(&cache_lru.list[ncp->nc_lrulist], ncp, nc_lru);
        TAILQ_INSERT_TAIL(&cache_lru.list[LRU_ACTIVE], ncp, nc_lru);
        cache_lru.count[ncp->nc_lrulist]--;