Re: [PATCH v8 0/8] mm: Hot page tracking and promotion infrastructure

[Bharata B Rao]

On 28-Sep-26 4:51 AM, Davidlohr Bueso wrote:
> On Wed, 16 Sep 2026, Bharata B Rao wrote:
> 
>> On 12-Sep-26 2:38 AM, Joshua Hahn wrote:
>>> - I also found a bug where the kmigrated thread isn't created for nodes
>>>   that are onlined later after boot, like CXL nodes that get onlined
>>>   with memory later on. I've been using a small hack commit in
>>>   pghot_memhp_callback that just checks for the MEM_ONLINE case and
>>>   spawns a kmigrated thread.
>>
>> I will take care of this scenario (CXL node online after boot) in my next
>> posting.
> 
> I was also running into this for chmu integration. I have been carrying the
> below in my own testing, fwiw.
> 
> Thanks,
> Davidlohr
> 
> -------------8<------------------------------------------
> diff --git a/mm/pghot.c b/mm/pghot.c
> index c7f523a61683..2f1e16e5091d 100644
> --- a/mm/pghot.c
> +++ b/mm/pghot.c
> @@ -602,6 +609,18 @@ static int kmigrated_run(int nid)
>      return 0;
>  }
>  
> +static void kmigrated_stop(int nid)
> +{
> +    pg_data_t *pgdat = NODE_DATA(nid);
> +    struct task_struct *t;
> +
> +    t = pgdat->kmigrated;
> +    if (t) {
> +        kthread_stop(t);
> +        pgdat->kmigrated = NULL;
> +    }
> +}
> +
>  static void pghot_free_hot_map(struct mem_section *ms)
>  {
>      struct pghot_hot_map *hot_map;
> @@ -707,6 +726,58 @@ static struct notifier_block pghot_mem_notifier = {
>      .priority = DEFAULT_CALLBACK_PRI,
>  };
>  
> +/*
> + * The first memory block of a node is onlined before the node gets
> + * assigned to a memory tier (memory tiers react to
> + * NODE_ADDED_FIRST_MEMORY at MEMTIER_HOTPLUG_PRI), so at
> + * MEM_GOING_ONLINE time for that block node_is_toptier() still
> + * returns true and pghot_online_sec_hotmap() skips it. Backfill the
> + * hot maps once the node tier is known.
> + */
> +static void pghot_alloc_node_hotmaps(int nid)
> +{
> +    unsigned long section_nr, s_begin, start_pfn;
> +    struct mem_section *ms;
> +    struct page *page;
> +
> +    s_begin = next_present_section_nr(-1);
> +    for_each_present_section_nr(s_begin, section_nr) {
> +        ms = __nr_to_section(section_nr);
> +        start_pfn = section_nr_to_pfn(section_nr);
> +
> +        page = pfn_to_online_page(start_pfn);
> +        if (!page || page_to_nid(page) != nid)
> +            continue;
> +
> +        if (rcu_access_pointer(ms->hot_map))
> +            continue;
> +
> +        if (pghot_alloc_hot_map(ms, nid))
> +            pr_warn("pghot: no hot map for section %lu on node %d\n",
> +                section_nr, nid);
> +    }
> +}
> +
> +static int pghot_node_callback(struct notifier_block *self,
> +                   unsigned long action, void *arg)
> +{
> +    struct node_notify *nn = arg;
> +
> +    switch (action) {
> +    case NODE_ADDED_FIRST_MEMORY:
> +        if (node_is_toptier(nn->nid))
> +            break;
> +        pghot_alloc_node_hotmaps(nn->nid);
> +        kmigrated_run(nn->nid);
> +        break;
> +    case NODE_REMOVED_LAST_MEMORY:
> +        kmigrated_stop(nn->nid);
> +        break;
> +    }
> +
> +    return NOTIFY_OK;
> +}
> +

I don't think we should allocate section hotmaps from node hotplug notifier
callback and let it get allocated from the already existing memory hotplug
notifier callback.

I have already taken care of node hotplug in my latest tree from which I posted
only the IBS Memory Profiler part.

https://github.com/AMDESE/linux-mm/tree/bharata/pghot-mprof-rfcv0

Regards,
Bharata.