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Message-ID: <b9965654-af90-42c9-8e4b-b29621d11ea7@amd.com>
Date: Mon, 17 Mar 2025 09:09:18 +0530
From: Bharata B Rao <bharata@....com>
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Subject: Re: [RFC PATCH 2/4] mm: kpromoted: Hot page info collection and
promotion daemon
On 13-Mar-25 10:14 PM, Davidlohr Bueso wrote:
> On Thu, 06 Mar 2025, Bharata B Rao wrote:
>
>> +static int page_should_be_promoted(struct page_hotness_info *phi)
>> +{
>> + struct page *page = pfn_to_online_page(phi->pfn);
>> + unsigned long now = jiffies;
>> + struct folio *folio;
>> +
>> + if (!page || is_zone_device_page(page))
>> + return false;
>> +
>> + folio = page_folio(page);
>> + if (!folio_test_lru(folio)) {
>> + count_vm_event(KPROMOTED_MIG_NON_LRU);
>> + return false;
>> + }
>> + if (folio_nid(folio) == phi->hot_node) {
>> + count_vm_event(KPROMOTED_MIG_RIGHT_NODE);
>> + return false;
>> + }
>
> How about using the LRU age itself:
Sounds like a good check for page hotness.
>
> if (folio_test_active())
> return true;
But the numbers I obtained with this check added, didn't really hit this
condition all that much. I was running a multi-threaded application that
allocates enough memory such that the allocation spills over from DRAM
node to the CXL node. Threads keep touching the memory pages in random
order.
kpromoted_recorded_accesses 960620 /* Number of recorded accesses */
kpromoted_recorded_hwhints 960620 /* Nr accesses via HW hints, IBS in
this case */
kpromoted_recorded_pgtscans 0
kpromoted_record_toptier 638006 /* Nr toptier accesses */
kpromoted_record_added 321234 /* Nr (CXL) accesses that are tracked */
kpromoted_record_exists 1380
kpromoted_mig_right_node 0
kpromoted_mig_non_lru 226
kpromoted_mig_lru_active 47 /* Number of accesses considered for
promotion as determined by folio_test_active() check */
kpromoted_mig_cold_old 0
kpromoted_mig_cold_not_accessed 1373
kpromoted_mig_candidate 319635
kpromoted_mig_promoted 319635
kpromoted_mig_dropped 1599
Need to check why is this the case.
>
>> +
>> + /* If the page was hot a while ago, don't promote */
>> + if ((now - phi->last_update) > 2 *
>> msecs_to_jiffies(KPROMOTED_FREQ_WINDOW)) {
>> + count_vm_event(KPROMOTED_MIG_COLD_OLD);
>> + return false;
>> + }
>> +
>> + /* If the page hasn't been accessed enough number of times, don't
>> promote */
>> + if (phi->frequency < KPRMOTED_FREQ_THRESHOLD) {
>> + count_vm_event(KPROMOTED_MIG_COLD_NOT_ACCESSED);
>> + return false;
>> + }
>> + return true;
>> +}
>
> ...
>
>> +static int kpromoted(void *p)
>> +{
>> + pg_data_t *pgdat = (pg_data_t *)p;
>> + struct task_struct *tsk = current;
>> + long timeout = msecs_to_jiffies(KPROMOTE_DELAY);
>> +
>> + const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>> +
>> + if (!cpumask_empty(cpumask))
>> + set_cpus_allowed_ptr(tsk, cpumask);
>
> Explicit cpumasks are not needed if you use kthread_create_on_node().
Thanks, will incorporate.
Regards,
Bharata.
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