Use memory purge redis command when initializing new kb

CHANGELOG.md

@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Add v3 handling to get_cvss_score_from_base_metrics. [#411](https://github.com/greenbone/gvm-libs/pull/411)
 - Add severity_date tag in epoch time format. [#412](https://github.com/greenbone/gvm-libs/pull/412)
 - Make more scanner preferences available to openvas-nasl. [#413](https://github.com/greenbone/gvm-libs/pull/413)
+- Use memory purge redis command when initializing new kb. [#452](https://github.com/greenbone/gvm-libs/pull/452)
 
 ### Changed
 - Add separators for a new (ip address) field in ERRMSG and DEADHOST messages. [#376](https://github.com/greenbone/gvm-libs/pull/376)

util/kb.c

@@ -380,6 +380,33 @@ redis_get_kb_index (kb_t kb)
   return -1;
 }
 
+/**
+ * @brief Attempt to purge dirty pages.
+ *
+ * Attempt to purge dirty pages so these can be reclaimed by the allocator.
+ * This command only works when using jemalloc as an allocator, and evaluates
+ * to a benign NOOP for all others. Command is applied to complete redis
+ * instance and not only single db.
+ *
+ * @param[in] kb KB handle where to run the command.
+ *
+ * @return 0 on success, non-null on error.
+ */
+static int
+redis_memory_purge (kb_t kb)
+{
+  redisReply *rep;
+  int rc = 0;
+
+  rep = redis_cmd (redis_kb (kb), "MEMORY PURGE");
+  if (!rep || rep->type == REDIS_REPLY_ERROR)
+    rc = -1;
+  if (rep)
+    freeReplyObject (rep);
+
+  return rc;
+}
+
 /**
  * @brief Initialize a new Knowledge Base object.
  *
@@ -413,6 +440,11 @@ redis_new (kb_t *kb, const char *kb_path)
     }
 
   *kb = (kb_t) kbr;
+
+  /* Try to make unused memory available for the OS again. */
+  if (redis_memory_purge (*kb))
+    g_warning ("%s: Memory purge was not successfull", __func__);
+
   return rc;
 }