Re: [PATCH 2/2] mm: thp: khugepaged: add policy for finding target node

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Tue, Sep 10, 2013 at 09:45:09AM +0900, Yasuaki Ishimatsu wrote:
>(2013/09/02 12:45), Bob Liu wrote:
>> Currently khugepaged will try to merge HPAGE_PMD_NR normal pages to a huge page
>> which is allocated from the node of the first normal page, this policy is very
>> rough and may affect userland applications.
>
>> Andrew Davidoff reported a related issue several days ago.
>
>Where is an original e-mail?
>I tried to find original e-mail in my mailbox. But I cannot find it.
>

http://marc.info/?l=linux-mm&m=137701470529356&w=2

>Thanks,
>Yasuaki Ishimatsu
>
>> 
>> Using "numactl --interleave=all ./test" to run the testcase, but the result
>> wasn't not as expected.
>> cat /proc/2814/numa_maps:
>> 7f50bd440000 interleave:0-3 anon=51403 dirty=51403 N0=435 N1=435 N2=435
>> N3=50098
>> The end results showed that most pages are from Node3 instead of interleave
>> among node0-3 which was unreasonable.
>> 
>> This patch adds a more complicated policy.
>> When searching HPAGE_PMD_NR normal pages, record which node those pages come
>> from. Alway allocate hugepage from the node with the max record. If several
>> nodes have the same max record, try to interleave among them.
>> 
>> After this patch the result was as expected:
>> 7f78399c0000 interleave:0-3 anon=51403 dirty=51403 N0=12723 N1=12723 N2=13235
>> N3=12722
>> 
>> The simple testcase is like this:
>> #include<stdio.h>
>> #include<stdlib.h>
>> 
>> int main() {
>> 	char *p;
>> 	int i;
>> 	int j;
>> 
>> 	for (i=0; i < 200; i++) {
>> 		p = (char *)malloc(1048576);
>> 		printf("malloc done\n");
>> 
>> 		if (p == 0) {
>> 			printf("Out of memory\n");
>> 			return 1;
>> 		}
>> 		for (j=0; j < 1048576; j++) {
>> 			p[j] = 'A';
>> 		}
>> 		printf("touched memory\n");
>> 
>> 		sleep(1);
>> 	}
>> 	printf("enter sleep\n");
>> 	while(1) {
>> 		sleep(100);
>> 	}
>> }
>> 
>> Reported-by: Andrew Davidoff <davidoff@qedmf.net>
>> Signed-off-by: Bob Liu <bob.liu@oracle.com>
>> ---
>>   mm/huge_memory.c |   50 +++++++++++++++++++++++++++++++++++++++++---------
>>   1 file changed, 41 insertions(+), 9 deletions(-)
>> 
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 7448cf9..86c7f0d 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2144,7 +2144,33 @@ static void khugepaged_alloc_sleep(void)
>>   			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
>>   }
>>   
>> +static int khugepaged_node_load[MAX_NUMNODES];
>>   #ifdef CONFIG_NUMA
>> +static int last_khugepaged_target_node = NUMA_NO_NODE;
>> +static int khugepaged_find_target_node(void)
>> +{
>> +	int i, target_node = 0, max_value = 1;
>> +
>> +	/* find first node with most normal pages hit */
>> +	for (i = 0; i < MAX_NUMNODES; i++)
>> +		if (khugepaged_node_load[i] > max_value) {
>> +			max_value = khugepaged_node_load[i];
>> +			target_node = i;
>> +		}
>> +
>> +	/* do some balance if several nodes have the same hit number */
>> +	if (target_node <= last_khugepaged_target_node) {
>> +		for (i = last_khugepaged_target_node + 1; i < MAX_NUMNODES; i++)
>> +			if (max_value == khugepaged_node_load[i]) {
>> +				target_node = i;
>> +				break;
>> +			}
>> +	}
>> +
>> +	last_khugepaged_target_node = target_node;
>> +	return target_node;
>> +}
>> +
>>   static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
>>   {
>>   	if (IS_ERR(*hpage)) {
>> @@ -2178,9 +2204,8 @@ static struct page
>>   	 * mmap_sem in read mode is good idea also to allow greater
>>   	 * scalability.
>>   	 */
>> -	*hpage  = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
>> -				      node, __GFP_OTHER_NODE);
>> -
>> +	*hpage = alloc_pages_exact_node(node, alloc_hugepage_gfpmask(
>> +			khugepaged_defrag(), __GFP_OTHER_NODE), HPAGE_PMD_ORDER);
>>   	/*
>>   	 * After allocating the hugepage, release the mmap_sem read lock in
>>   	 * preparation for taking it in write mode.
>> @@ -2196,6 +2221,11 @@ static struct page
>>   	return *hpage;
>>   }
>>   #else
>> +static int khugepaged_find_target_node(void)
>> +{
>> +	return 0;
>> +}
>> +
>>   static inline struct page *alloc_hugepage(int defrag)
>>   {
>>   	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
>> @@ -2405,6 +2435,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>>   	if (pmd_trans_huge(*pmd))
>>   		goto out;
>>   
>> +	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
>>   	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
>>   	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
>>   	     _pte++, _address += PAGE_SIZE) {
>> @@ -2421,12 +2452,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>>   		if (unlikely(!page))
>>   			goto out_unmap;
>>   		/*
>> -		 * Chose the node of the first page. This could
>> -		 * be more sophisticated and look at more pages,
>> -		 * but isn't for now.
>> +		 * Chose the node of most normal pages hit, record this
>> +		 * informaction to khugepaged_node_load[]
>>   		 */
>> -		if (node == NUMA_NO_NODE)
>> -			node = page_to_nid(page);
>> +		node = page_to_nid(page);
>> +		khugepaged_node_load[node]++;
>>   		VM_BUG_ON(PageCompound(page));
>>   		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
>>   			goto out_unmap;
>> @@ -2441,9 +2471,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>>   		ret = 1;
>>   out_unmap:
>>   	pte_unmap_unlock(pte, ptl);
>> -	if (ret)
>> +	if (ret) {
>> +		node = khugepaged_find_target_node();
>>   		/* collapse_huge_page will return with the mmap_sem released */
>>   		collapse_huge_page(mm, address, hpage, vma, node);
>> +	}
>>   out:
>>   	return ret;
>>   }
>> 
>
>
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