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

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Message-Id: <C79B8BB3-C1F8-4DFA-A084-C4B47486681F@linux.dev>
Date: Tue, 23 Jan 2024 11:32:28 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Gang Li <gang.li@...ux.dev>
Cc: David Hildenbrand <david@...hat.com>,
 David Rientjes <rientjes@...gle.com>,
 Mike Kravetz <mike.kravetz@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Tim Chen <tim.c.chen@...ux.intel.com>,
 Linux-MM <linux-mm@...ck.org>,
 LKML <linux-kernel@...r.kernel.org>,
 Gang Li <ligang.bdlg@...edance.com>
Subject: Re: [PATCH v4 6/7] hugetlb: parallelize 2M hugetlb allocation and
 initialization



> On Jan 23, 2024, at 10:12, Gang Li <gang.li@...ux.dev> wrote:
> 
> On 2024/1/22 19:30, Muchun Song wrote:
>>> On Jan 22, 2024, at 18:12, Gang Li <gang.li@...ux.dev> 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);
> }
> ```