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

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Message-ID: <5017862d-98d7-4f4a-8272-88bcdfa78fcb@amd.com>
Date: Thu, 6 Mar 2025 11:22:26 -0600
From: Mike Day <michael.day@....com>
To: Bharata B Rao <bharata@....com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Cc: AneeshKumar.KizhakeVeetil@....com, Hasan.Maruf@....com,
 Jonathan.Cameron@...wei.com, akpm@...ux-foundation.org,
 dave.hansen@...el.com, david@...hat.com, feng.tang@...el.com,
 gourry@...rry.net, hannes@...xchg.org, honggyu.kim@...com, hughd@...gle.com,
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Subject: Re: [RFC PATCH 2/4] mm: kpromoted: Hot page info collection and
 promotion daemon



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?

Mike
> +		if (phi->pfn == pfn)
> +			return phi;
> +	}
> +	return NULL;
> +}