linux-kernel - Re: [PATCH v2] mm/hugeltb: fix nodes huge page allocation when there are surplus pages

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Message-ID: <20230829165707.GB5644@monkey>
Date:   Tue, 29 Aug 2023 09:57:07 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Xueshi Hu <xueshi.hu@...rtx.com>
Cc:     Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <andi@...stfloor.org>,
        Lee Schermerhorn <lee.schermerhorn@...com>,
        Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/hugeltb: fix nodes huge page allocation when there
 are surplus pages

On 08/29/23 11:33, Xueshi Hu wrote:
> In set_nr_huge_pages(), local variable "count" is used to record
> persistent_huge_pages(), but when it cames to nodes huge page allocation,
> the semantics changes to nr_huge_pages. When there exists surplus huge
> pages and using the interface under
> /sys/devices/system/node/node*/hugepages to change huge page pool size,
> this difference can result in the allocation of an unexpected number of
> huge pages.
> 
> Steps to reproduce the bug:
> 
> Starting with:
> 
> 				  Node 0          Node 1    Total
> 	HugePages_Total             0.00            0.00     0.00
> 	HugePages_Free              0.00            0.00     0.00
> 	HugePages_Surp              0.00            0.00     0.00
> 
> create 100 huge pages in Node 0 and consume it, then set Node 0 's
> nr_hugepages to 0.
> 
> yields:
> 
> 				  Node 0          Node 1    Total
> 	HugePages_Total           200.00            0.00   200.00
> 	HugePages_Free              0.00            0.00     0.00
> 	HugePages_Surp            200.00            0.00   200.00
> 
> write 100 to Node 1's nr_hugepages
> 
> 		echo 100 > /sys/devices/system/node/node1/\
> 	hugepages/hugepages-2048kB/nr_hugepages
> 
> gets:
> 
> 				  Node 0          Node 1    Total
> 	HugePages_Total           200.00          400.00   600.00
> 	HugePages_Free              0.00          400.00   400.00
> 	HugePages_Surp            200.00            0.00   200.00
> 
> Kernel is expected to create only 100 huge pages and it gives 200.
> 
> Fixes: 9a30523066cd ("hugetlb: add per node hstate attributes")
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Xueshi Hu <xueshi.hu@...rtx.com>
> ---
> Change in v2:
> - Correct the fix tag

Thank you!
-- 
Mike Kravetz

> - v1: https://lore.kernel.org/linux-mm/20230828233448.GF3290@monkey/T/#t
> 
>  mm/hugetlb.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6da626bfb52e..54e2e2e12aa9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -3494,7 +3494,9 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>  	if (nid != NUMA_NO_NODE) {
>  		unsigned long old_count = count;
>  
> -		count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
> +		count += persistent_huge_pages(h) -
> +			 (h->nr_huge_pages_node[nid] -
> +			  h->surplus_huge_pages_node[nid]);
>  		/*
>  		 * User may have specified a large count value which caused the
>  		 * above calculation to overflow.  In this case, they wanted
> -- 
> 2.40.1
>