Re: [PATCH] mm/hugetlb: fix set_max_huge_pages() when there are surplus pages

[Jinjiang Tu <tujinjiang@huawei.com>]

在 2025/2/26 23:57, David Hildenbrand 写道:
> On 25.02.25 15:19, Jinjiang Tu wrote:
>> In set_max_huge_pages(), min_count should mean the acquired persistent
>> huge pages, but it contains surplus huge pages. It will leads to failing
>
> s/leads/lead/
>
>> to freeing free huge pages for a Node.
>>
>> Steps to reproduce:
>> 1) create 5 huge pages in Node 0
>> 2) run a program to use all the huge pages
>> 3) create 5 huge pages in Node 1
>> 4) echo 0 > nr_hugepages for Node 1 to free the huge pages
>>
>> The result:
>>          Node 0    Node 1
>> Total     5         5
>> Free      0         5
>> Surp      5         5
>
> Can you also share the results after your change?
With this patch, step 4) destroys the 5 huge pages in Node 1

The result with this patch:
          Node 0    Node 1
Total     5             0
Free      0             0
Surp     5             0
>
>
>>
>> Fixes: 9a30523066cd ("hugetlb: add per node hstate attributes")
>> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
>> ---
>>   mm/hugetlb.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 163190e89ea1..783faec7360b 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -3758,7 +3758,7 @@ static int set_max_huge_pages(struct hstate *h, 
>> unsigned long count, int nid,
>>        * and won't grow the pool anywhere else. Not until one of the
>>        * sysctls are changed, or the surplus pages go out of use.
>>        */
>> -    min_count = h->resv_huge_pages + h->nr_huge_pages - 
>> h->free_huge_pages;
>> +    min_count = h->resv_huge_pages + persistent_huge_pages(h) - 
>> h->free_huge_pages;
>>       min_count = max(count, min_count);
>>       try_to_free_low(h, min_count, nodes_allowed);
>
>