Re: [RFC PATCH 2/4] mm: kpromoted: Hot page info collection and promotion daemon

[Bharata B Rao]

On 06-Mar-25 10:52 PM, Mike Day wrote:
> On 3/5/25 23:45, Bharata B Rao wrote:
> > +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?
> > +                 */
> > +                count_vm_event(KPROMOTED_MIG_DROPPED);
> > +                hlist_del_init(&phi->hnode);
> > +                kfree(phi);
> > +            }
> > +        }
> > +        mutex_unlock(&page_hotness_lock[bkt]);
> > +    }
> > +}
> > +
> > +static struct page_hotness_info *__kpromoted_lookup(unsigned long 
> > pfn, int bkt)
> > +{
> > +    struct page_hotness_info *phi;
> > +
> > +    hlist_for_each_entry(phi, &page_hotness_hash[bkt], hnode) {
>
> Should this be hlist_for_each_entry_safe(), given that 
> kpromoted_migrate() may be
> running concurrently?

I don't think so because the migration path can't walk the list 
concurrently as the lists are protected by mutex.

Regards,
Bharata.