resolved: try to reduce number or DnsResourceKeys we keep around by merging them

Quite often we read the same RR key multiple times from the same message. Try to replace them by a single object when
we notice this. Do so again when we add things to the cache.

This should reduce memory consumption a tiny bit.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
index 301f383809..fdb34d11df 100644
--- a/src/resolve/resolved-dns-cache.c
+++ b/src/resolve/resolved-dns-cache.c
@@ -247,6 +247,19 @@ static int dns_cache_link_item(DnsCache *c, DnsCacheItem *i) {
 
         first = hashmap_get(c->by_key, i->key);
         if (first) {
+                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *k = NULL;
+
+                /* Keep a reference to the original key, while we manipulate the list. */
+                k = dns_resource_key_ref(first->key);
+
+                /* Now, try to reduce the number of keys we keep */
+                dns_resource_key_reduce(&first->key, &i->key);
+
+                if (first->rr)
+                        dns_resource_key_reduce(&first->rr->key, &i->key);
+                if (i->rr)
+                        dns_resource_key_reduce(&i->rr->key, &i->key);
+
                 LIST_PREPEND(by_key, first, i);
                 assert_se(hashmap_replace(c->by_key, first->key, first) >= 0);
         } else {