kernel - Change namecache negative caching algorithm

* Use desiredvnodes instead of numcache (current number of namecache
  entries) to scale the number of negative cache entries.

  This allows for more negative cache entries and no longer has
  degenerate situations when the value of numcache is low.

* namecache entries are still cleaned up in the critical namecache
  paths, but vnlru() now also cleans up the namecache when it exceeds
  80% of its nominal maximum.  The result is that the namecache is
  kept under better control AND the cleanups are generally able to be
  handled by vnlru() and do not effect the critical paths.

* Huge improvement in poudriere during concurrent python easy_install
  execution.  The python easy_install performs horribly without sufficient
  negative caching.  This fixes that.

Reported-by: thesjg

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index c415c3a..3f77e75 100644 (file)
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -167,6 +167,14 @@ static u_long      nchash;                 /* size of hash table */
 SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0,
     "Size of namecache hash table");
 
+static int     ncnegflush = 10;        /* burst for negative flush */
+SYSCTL_INT(_debug, OID_AUTO, ncnegflush, CTLFLAG_RW, &ncnegflush, 0,
+    "Batch flush negative entries");
+
+static int     ncposflush = 10;        /* burst for positive flush */
+SYSCTL_INT(_debug, OID_AUTO, ncposflush, CTLFLAG_RW, &ncposflush, 0,
+    "Batch flush positive entries");
+
 static int     ncnegfactor = 16;       /* ratio of negative entries */
 SYSCTL_INT(_debug, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0,
     "Ratio of namecache negative entries");
@@ -2486,35 +2494,53 @@ cache_zap(struct namecache *ncp, int nonblock)
 /*
  * Clean up dangling negative cache and defered-drop entries in the
  * namecache.
+ *
+ * This routine is called in the critical path and also called from
+ * vnlru().  When called from vnlru we use a lower limit to try to
+ * deal with the negative cache before the critical path has to start
+ * dealing with it.
  */
 typedef enum { CHI_LOW, CHI_HIGH } cache_hs_t;
 
-static cache_hs_t neg_cache_hysteresis_state = CHI_LOW;
-static cache_hs_t pos_cache_hysteresis_state = CHI_LOW;
+static cache_hs_t neg_cache_hysteresis_state[2] = { CHI_LOW, CHI_LOW };
+static cache_hs_t pos_cache_hysteresis_state[2] = { CHI_LOW, CHI_LOW };
 
 void
-cache_hysteresis(void)
+cache_hysteresis(int critpath)
 {
        int poslimit;
+       int neglimit = desiredvnodes / ncnegfactor;
+       int xnumcache = numcache;
+
+       if (critpath == 0)
+               neglimit = neglimit * 8 / 10;
 
        /*
         * Don't cache too many negative hits.  We use hysteresis to reduce
         * the impact on the critical path.
         */
-       switch(neg_cache_hysteresis_state) {
+       switch(neg_cache_hysteresis_state[critpath]) {
        case CHI_LOW:
-               if (numneg > MINNEG && numneg * ncnegfactor > numcache) {
-                       _cache_cleanneg(10);
-                       neg_cache_hysteresis_state = CHI_HIGH;
+               if (numneg > MINNEG && numneg > neglimit) {
+                       if (critpath)
+                               _cache_cleanneg(ncnegflush);
+                       else
+                               _cache_cleanneg(ncnegflush +
+                                               numneg - neglimit);
+                       neg_cache_hysteresis_state[critpath] = CHI_HIGH;
                }
                break;
        case CHI_HIGH:
                if (numneg > MINNEG * 9 / 10 && 
-                   numneg * ncnegfactor * 9 / 10 > numcache
+                   numneg * 9 / 10 > neglimit
                ) {
-                       _cache_cleanneg(10);
+                       if (critpath)
+                               _cache_cleanneg(ncnegflush);
+                       else
+                               _cache_cleanneg(ncnegflush +
+                                               numneg * 9 / 10 - neglimit);
                } else {
-                       neg_cache_hysteresis_state = CHI_LOW;
+                       neg_cache_hysteresis_state[critpath] = CHI_LOW;
                }
                break;
        }
@@ -2529,19 +2555,29 @@ cache_hysteresis(void)
         */
        if ((poslimit = ncposlimit) == 0)
                poslimit = desiredvnodes * 2;
+       if (critpath == 0)
+               poslimit = poslimit * 8 / 10;
 
-       switch(pos_cache_hysteresis_state) {
+       switch(pos_cache_hysteresis_state[critpath]) {
        case CHI_LOW:
-               if (numcache > poslimit && numcache > MINPOS) {
-                       _cache_cleanpos(10);
-                       pos_cache_hysteresis_state = CHI_HIGH;
+               if (xnumcache > poslimit && xnumcache > MINPOS) {
+                       if (critpath)
+                               _cache_cleanpos(ncposflush);
+                       else
+                               _cache_cleanpos(ncposflush +
+                                               xnumcache - poslimit);
+                       pos_cache_hysteresis_state[critpath] = CHI_HIGH;
                }
                break;
        case CHI_HIGH:
-               if (numcache > poslimit * 5 / 6 && numcache > MINPOS) {
-                       _cache_cleanpos(10);
+               if (xnumcache > poslimit * 5 / 6 && xnumcache > MINPOS) {
+                       if (critpath)
+                               _cache_cleanpos(ncposflush);
+                       else
+                               _cache_cleanpos(ncposflush +
+                                               xnumcache - poslimit * 5 / 6);
                } else {
-                       pos_cache_hysteresis_state = CHI_LOW;
+                       pos_cache_hysteresis_state[critpath] = CHI_LOW;
                }
                break;
        }
@@ -2553,7 +2589,7 @@ cache_hysteresis(void)
         * can be reused and the counter is not handled in a MP
         * safe manner by design.
         */
-       if (numdefered * ncnegfactor > numcache) {
+       if (numdefered > neglimit) {
                _cache_cleandefered();
        }
 }
@@ -2613,7 +2649,7 @@ cache_nlookup(struct nchandle *par_nch, struct nlcomponent *nlc)
         * This is a good time to call it, no ncp's are locked by
         * the caller or us.
         */
-       cache_hysteresis();
+       cache_hysteresis(1);
 
        /*
         * Try to locate an existing entry
@@ -2738,7 +2774,7 @@ cache_nlookup_maybe_shared(struct nchandle *par_nch, struct nlcomponent *nlc,
         * This is a good time to call it, no ncp's are locked by
         * the caller or us.
         */
-       cache_hysteresis();
+       cache_hysteresis(1);
 
        /*
         * Try to locate an existing entry

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 3024a5b..e50dbe7 100644 (file)
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -726,6 +726,13 @@ vnlru_proc(void)
                }
 
                /*
+                * Do non-critical-path (more robust) cache cleaning,
+                * even if vnode counts are nominal, to try to avoid
+                * having to do it in the critical path.
+                */
+               cache_hysteresis(0);
+
+               /*
                 * Nothing to do if most of our vnodes are already on
                 * the free list.
                 */
@@ -733,7 +740,6 @@ vnlru_proc(void)
                        tsleep(vnlruthread, 0, "vlruwt", hz);
                        continue;
                }
-               cache_hysteresis();
 
                /*
                 * The pass iterates through the four combinations of

diff --git a/sys/sys/namecache.h b/sys/sys/namecache.h
index 693a3cf..6c202e6 100644 (file)
--- a/sys/sys/namecache.h
+++ b/sys/sys/namecache.h
@@ -209,7 +209,7 @@ void        vfs_cache_setroot(struct vnode *vp, struct nchandle *nch);
 int    cache_resolve(struct nchandle *nch, struct ucred *cred);
 void   cache_purge(struct vnode *vp);
 void   cache_purgevfs (struct mount *mp);
-void   cache_hysteresis(void);
+void   cache_hysteresis(int critpath);
 void   cache_get(struct nchandle *nch, struct nchandle *target);
 int    cache_get_nonblock(struct nchandle *nch, struct nchandle *target);
 void   cache_get_maybe_shared(struct nchandle *nch,