Here is a new patch set. I missed a case in cache_nlookup(). The other
patch will work but might still result in unnecessary vnlru process
wakeups.
The hysteresis is designed such that in a heavily loaded system only 1
out of 10 calls to the namecache will eat cpu cycles cleaning up negative
cache entries.
-Matt
Index: sys/namecache.h
===================================================================
RCS file: /cvs/src/sys/sys/namecache.h,v
retrieving revision 1.13
diff -u -r1.13 namecache.h
--- sys/namecache.h 12 Oct 2004 19:20:48 -0000 1.13
+++ sys/namecache.h 18 Oct 2004 20:35:08 -0000
@@ -164,6 +164,7 @@
void cache_purge(struct vnode *vp);
void cache_purgevfs (struct mount *mp);
int cache_get_nonblock(struct namecache *ncp);
+void cache_cleanneg(int count);
struct namecache *cache_get(struct namecache *ncp);
struct namecache *cache_hold(struct namecache *ncp);
void cache_put(struct namecache *ncp);
Index: kern/vfs_cache.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_cache.c,v
retrieving revision 1.38
diff -u -r1.38 vfs_cache.c
--- kern/vfs_cache.c 12 Oct 2004 19:20:46 -0000 1.38
+++ kern/vfs_cache.c 18 Oct 2004 21:58:16 -0000
@@ -777,6 +777,38 @@
--ncp->nc_refs;
}
+static enum { CHI_LOW, CHI_HIGH } cache_hysteresis_state = CHI_LOW;
+
+static __inline
+void
+cache_hysteresis(void)
+{
+ /*
+ * Don't cache too many negative hits. We use hysteresis to reduce
+ * the impact on the critical path.
+ */
+ switch(cache_hysteresis_state) {
+ case CHI_LOW:
+ if (numneg > MINNEG && numneg * ncnegfactor > numcache) {
+ cache_cleanneg(10);
+ if (cache_hysteresis_state == CHI_LOW)
+ printf("H");
+ cache_hysteresis_state = CHI_HIGH;
+ }
+ break;
+ case CHI_HIGH:
+ if (numneg > MINNEG * 9 / 10 &&
+ numneg * ncnegfactor * 9 / 10 > numcache
+ ) {
+ cache_cleanneg(10);
+ } else {
+ cache_hysteresis_state = CHI_LOW;
+ printf("L");
+ }
+ break;
+ }
+}
+
/*
* NEW NAMECACHE LOOKUP API
*
@@ -883,6 +915,7 @@
ncp->nc_flag |= NCF_HASHED;
cache_link_parent(ncp, par);
found:
+ cache_hysteresis();
return(ncp);
}
@@ -1388,15 +1421,35 @@
ncp->nc_flag |= NCF_WHITEOUT;
}
cache_put(ncp);
+ cache_hysteresis();
+}
+
+void
+cache_cleanneg(int count)
+{
+ struct namecache *ncp;
+
+ /*
+ * Automode from the vnlru proc - clean out 10% of the negative cache
+ * entries.
+ */
+ if (count == 0) {
+ count = numneg / 10 + 1;
+ printf("X");
+ }
/*
- * Don't cache too many negative hits
+ * Attempt to clean out the specified number of negative cache
+ * entries.
*/
- if (numneg > MINNEG && numneg * ncnegfactor > numcache) {
+ while (count) {
ncp = TAILQ_FIRST(&ncneglist);
KKASSERT(ncp != NULL);
+ TAILQ_REMOVE(&ncneglist, ncp, nc_vnode);
+ TAILQ_INSERT_TAIL(&ncneglist, ncp, nc_vnode);
if (cache_get_nonblock(ncp) == 0)
cache_zap(ncp);
+ --count;
}
}
Index: kern/vfs_mount.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_mount.c,v
retrieving revision 1.1
diff -u -r1.1 vfs_mount.c
--- kern/vfs_mount.c 12 Oct 2004 19:20:46 -0000 1.1
+++ kern/vfs_mount.c 18 Oct 2004 20:34:52 -0000
@@ -470,6 +470,7 @@
continue;
}
done = 0;
+ cache_cleanneg(0);
lwkt_gettoken(&ilock, &mountlist_token);
for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
if (vfs_busy(mp, LK_NOWAIT, &ilock, td)) {