net: add a route cache full diagnostic message

In some testing scenarios, dst/route cache can fill up so quickly
that even an explicit GC call occasionally fails to clean it up. This leads
to sporadically failing calls to dst_alloc and "network unreachable" errors
to the user, which is confusing.

This patch adds a diagnostic message to make the cause of the failure
easier to determine.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dst.c b/net/core/dst.c
index 81ccf20e28265ec61c2a4025b8f8f1f65f38c866..a263309df115ee5157f3cd6c7bec88c8ce02fe09 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -98,8 +98,12 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
        struct dst_entry *dst;
 
        if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
-               if (ops->gc(ops))
+               if (ops->gc(ops)) {
+                       printk_ratelimited(KERN_NOTICE "Route cache is full: "
+                                          "consider increasing sysctl "
+                                          "net.ipv[4|6].route.max_size.\n");
                        return NULL;
+               }
        }
 
        dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);