+
+/*
+ * Monitor the amount of available backing store vs. the amount of
+ * required backing store, notify a listener (if present) when
+ * backing store may safely be removed.
+ *
+ * We attempt to avoid the situation where backing store is
+ * discarded en masse, as this can lead to thrashing as the
+ * backing store is compacted.
+ */
+
+#define PF_INTERVAL 3 /* time between free level checks */
+#define PF_LATENCY 10 /* number of intervals before release */
+
+static int dp_pages_free_low_count = 0;
+
+void
+default_pager_backing_store_monitor(thread_call_param_t p1, thread_call_param_t p2)
+{
+ unsigned long long average;
+ ipc_port_t trigger;
+ uint64_t deadline;
+
+ /*
+ * We determine whether it will be safe to release some
+ * backing store by watching the free page level. If
+ * it remains below the maximum_pages_free threshold for
+ * at least PF_LATENCY checks (taken at PF_INTERVAL seconds)
+ * then we deem it safe.
+ *
+ * Note that this establishes a maximum rate at which backing
+ * store will be released, as each notification (currently)
+ * only results in a single backing store object being
+ * released.
+ */
+ if (dp_pages_free > maximum_pages_free) {
+ dp_pages_free_low_count++;
+ } else {
+ dp_pages_free_low_count = 0;
+ }
+
+ /* decide whether to send notification */
+ trigger = IP_NULL;
+ if (max_pages_trigger_port &&
+ (backing_store_release_trigger_disable == 0) &&
+ (dp_pages_free_low_count > PF_LATENCY)) {
+ trigger = max_pages_trigger_port;
+ max_pages_trigger_port = NULL;
+ }
+
+ /* send notification */
+ if (trigger != IP_NULL) {
+ VSL_LOCK();
+ if(backing_store_release_trigger_disable != 0) {
+ assert_wait((event_t)
+ &backing_store_release_trigger_disable,
+ THREAD_UNINT);
+ VSL_UNLOCK();
+ thread_block(THREAD_CONTINUE_NULL);
+ } else {
+ VSL_UNLOCK();
+ }
+ default_pager_space_alert(trigger, LO_WAT_ALERT);
+ ipc_port_release_send(trigger);
+ dp_pages_free_low_count = 0;
+ }
+
+ clock_interval_to_deadline(PF_INTERVAL, NSEC_PER_SEC, &deadline);
+ thread_call_func_delayed(default_pager_backing_store_monitor, NULL, deadline);
+}
projects / apple / xnu.git / blobdiff