linux-kernel - Re: [PATCH] mm/khugepaged: sched to numa node when collapse huge page

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Message-ID: <d2883450-1278-877e-e273-bda5a5728465@loongson.cn>
Date:   Fri, 11 Mar 2022 17:51:54 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/khugepaged: sched to numa node when collapse huge page



On 03/11/2022 05:20 PM, David Hildenbrand wrote:
> On 11.03.22 10:01, Bibo Mao wrote:
>> collapse huge page is slow, specially when khugepaged daemon runs
>> on different numa node with that of huge page. It suffers from
>> huge page copying across nodes, also cache is not used for target
>> node. With this patch, khugepaged daemon switches to the same numa
>> node with huge page. It saves copying time and makes use of local
>> cache better.
> 
> Hi,
> 
> just the usual question, do you have any performance numbers to back
> your claims (e.g., "is slow, specially when") and proof that this patch
> does the trick?
With specint 2006 on loongarch 3C5000L 32core numa system, it improves
about 6%. The page size is 16K and pmd page size is 32M, memory performance
across numa node is obvious different. However I do not test it on x86 box.


> 
> 
>>
>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>> ---
>>  mm/khugepaged.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index 131492fd1148..460c285dc974 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -116,6 +116,7 @@ struct khugepaged_scan {
>>  	struct list_head mm_head;
>>  	struct mm_slot *mm_slot;
>>  	unsigned long address;
>> +	int node;
>>  };
>>  
>>  static struct khugepaged_scan khugepaged_scan = {
>> @@ -1066,6 +1067,7 @@ static void collapse_huge_page(struct mm_struct *mm,
>>  	struct vm_area_struct *vma;
>>  	struct mmu_notifier_range range;
>>  	gfp_t gfp;
>> +	const struct cpumask *cpumask;
> 
> We tend to stick to reverse Christmas tree format as good as possible.
> 
>>  
>>  	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
>>  
>> @@ -1079,6 +1081,13 @@ static void collapse_huge_page(struct mm_struct *mm,
>>  	 * that. We will recheck the vma after taking it again in write mode.
>>  	 */
>>  	mmap_read_unlock(mm);
>> +
>> +	/* sched to specified node before huage page memory copy */
> 
> s/huage/huge/
> 
>> +	cpumask = cpumask_of_node(node);
>> +	if ((khugepaged_scan.node != node) && !cpumask_empty(cpumask)) {
>> +		set_cpus_allowed_ptr(current, cpumask);
>> +		khugepaged_scan.node = node;
>> +	}
>>  	new_page = khugepaged_alloc_page(hpage, gfp, node);
>>  	if (!new_page) {
>>  		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
>> @@ -2380,6 +2389,7 @@ int start_stop_khugepaged(void)
>>  		kthread_stop(khugepaged_thread);
>>  		khugepaged_thread = NULL;
>>  	}
>> +	khugepaged_scan.node = NUMA_NO_NODE;
>>  	set_recommended_min_free_kbytes();
>>  fail:
>>  	mutex_unlock(&khugepaged_mutex);
> 
>