On Thu, 06 Mar 2025, Bharata B Rao wrote:
+/*
+ * Go thro' page hotness information and migrate pages if required.
+ *
+ * Promoted pages are not longer tracked in the hot list.
+ * Cold pages are pruned from the list as well.
+ *
+ * TODO: Batching could be done
+ */
+static void kpromoted_migrate(pg_data_t *pgdat)
+{
+ int nid = pgdat->node_id;
+ struct page_hotness_info *phi;
+ struct hlist_node *tmp;
+ int nr_bkts = HASH_SIZE(page_hotness_hash);
+ int bkt;
+
+ for (bkt = 0; bkt < nr_bkts; bkt++) {
+ mutex_lock(&page_hotness_lock[bkt]);
+ hlist_for_each_entry_safe(phi, tmp, &page_hotness_hash[bkt], hnode) {
+ if (phi->hot_node != nid)
+ continue;
+
+ if (page_should_be_promoted(phi)) {
+ count_vm_event(KPROMOTED_MIG_CANDIDATE);
+ if (!kpromote_page(phi)) {
+ count_vm_event(KPROMOTED_MIG_PROMOTED);
+ hlist_del_init(&phi->hnode);
+ kfree(phi);
+ }
+ } else {
+ /*
+ * Not a suitable page or cold page, stop tracking it.
+ * TODO: Identify cold pages and drive demotion?
+ */
I don't think kpromoted should drive demotion at all. No one is complaining about migrate
in lieu of discard, and there is also proactive reclaim which users can trigger. All the
in-kernel problems are wrt promotion. The simpler any of these kthreads are the better.
+ count_vm_event(KPROMOTED_MIG_DROPPED);
+ hlist_del_init(&phi->hnode);
+ kfree(phi);
+ }
+ }
+ mutex_unlock(&page_hotness_lock[bkt]);
+ }
+}
