Re: [PATCH v4 6/7] hugetlb: parallelize 2M hugetlb allocation and initialization

[Muchun Song]

> On Jan 23, 2024, at 10:12, Gang Li <gang.li@xxxxxxxxx> wrote:
> 
> On 2024/1/22 19:30, Muchun Song wrote:
>>> On Jan 22, 2024, at 18:12, Gang Li <gang.li@xxxxxxxxx> wrote:
>>> 
>>> On 2024/1/22 15:10, Muchun Song wrote:> On 2024/1/18 20:39, Gang Li wrote:
>>>>> +static void __init hugetlb_alloc_node(unsigned long start, unsigned long end, void *arg)
>>>>>   {
>>>>> -    unsigned long i;
>>>>> +    struct hstate *h = (struct hstate *)arg;
>>>>> +    int i, num = end - start;
>>>>> +    nodemask_t node_alloc_noretry;
>>>>> +    unsigned long flags;
>>>>> +    int next_node = 0;
>>>> This should be first_online_node which may be not zero.
>>> 
>>> That's right. Thanks!
>>> 
>>>>> -    for (i = 0; i < h->max_huge_pages; ++i) {
>>>>> -        if (!alloc_bootmem_huge_page(h, NUMA_NO_NODE))
>>>>> +    /* Bit mask controlling how hard we retry per-node allocations.*/
>>>>> +    nodes_clear(node_alloc_noretry);
>>>>> +
>>>>> +    for (i = 0; i < num; ++i) {
>>>>> +        struct folio *folio = alloc_pool_huge_folio(h, &node_states[N_MEMORY],
>>>>> +                        &node_alloc_noretry, &next_node);
>>>>> +        if (!folio)
>>>>>               break;
>>>>> +        spin_lock_irqsave(&hugetlb_lock, flags);
>>>>> I suspect there will more contention on this lock when parallelizing.
>>> 
>>> In the worst case, there are only 'numa node number' of threads in
>>> contention. And in my testing, it doesn't degrade performance, but
>>> rather improves performance due to the reduced granularity.
>> So, the performance does not change if you move the lock out of
>> loop?
>> 
> 
> If we move the lock out of loop, then multi-threading becomes single-threading, which definitely reduces performance.

No. I mean batching the pages into pool list just like prep_and_add_allocated_folios
does.

> 
> ```
> +       spin_lock_irqsave(&hugetlb_lock, flags);
>        for (i = 0; i < num; ++i) {
>                struct folio *folio = alloc_pool_huge_folio(h, &node_states[N_MEMORY],
>                                                &node_alloc_noretry, &next_node);
>                if (!folio)
>                        break;
> -               spin_lock_irqsave(&hugetlb_lock, flags);
>                __prep_account_new_huge_page(h, folio_nid(folio));
>                enqueue_hugetlb_folio(h, folio);
> -               spin_unlock_irqrestore(&hugetlb_lock, flags);
>                cond_resched();
>        }
> +       spin_unlock_irqrestore(&hugetlb_lock, flags);
> }
> ```