neigh: Keep neighbour cache entries if number of them is small enough.

Since we have removed NCE (Neighbour Cache Entry) reference from
routing entries, the only refcnt holders of an NCE are its timer
(if running) and its owner table, in usual cases.  As a result,
neigh_periodic_work() purges NCEs over and over again even for
gateways.

It does not make sense to purge entries, if number of them is
very small, so keep them.  The minimum number of entries to keep
is specified by gc_thresh1.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 497656473b1c..19ac1802bfd4 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -26,6 +26,11 @@ route/max_size - INTEGER
         Maximum number of routes allowed in the kernel.  Increase
         this when using large numbers of interfaces and/or routes.
 
+neigh/default/gc_thresh1 - INTEGER
+        Minimum number of entries to keep.  Garbage collector will not
+        purge entries if there are fewer than this number.
+        Default: 256
+
 neigh/default/gc_thresh3 - INTEGER
         Maximum number of neighbor entries allowed.  Increase this
         when using large numbers of interfaces and when communicating
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index c815f285e5ab..7bd0eedb357f 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -778,6 +778,9 @@ static void neigh_periodic_work(struct work_struct *work)
         nht = rcu_dereference_protected(tbl->nht,
                                         lockdep_is_held(&tbl->lock));
 
+        if (atomic_read(&tbl->entries) < tbl->gc_thresh1)
+                goto out;
+
         /*
          *      periodically recompute ReachableTime from random function
          */
@@ -832,6 +835,7 @@ next_elt:
                 nht = rcu_dereference_protected(tbl->nht,
                                                 lockdep_is_held(&tbl->lock));
         }
+out:
         /* Cycle through all hash buckets every base_reachable_time/2 ticks.
          * ARP entry timeouts range from 1/2 base_reachable_time to 3/2
          * base_reachable_time.