linux-kernel - Re: [PATCH] mm: hugetlb: remove minimum

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Date:   Thu, 16 Jun 2022 05:50:57 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: hugetlb: remove minimum_order variable

On Thu, Jun 16, 2022 at 11:38:46AM +0800, Muchun Song wrote:
> The following commit:
> 
>   commit 641844f5616d ("mm/hugetlb: introduce minimum hugepage order")
> 
> fixed a static checker warning and introduced a global variable minimum_order
> to fix the warning.  However, the local variable in dissolve_free_huge_pages()
> can be initialized to huge_page_order(&default_hstate) to fix the warning.
> So remove minimum_order to simplify the code.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  mm/hugetlb.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8ea4e51d8186..405d1c7441c9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -66,12 +66,6 @@ static bool hugetlb_cma_page(struct page *page, unsigned int order)
>  #endif
>  static unsigned long hugetlb_cma_size __initdata;
>  
> -/*
> - * Minimum page order among possible hugepage sizes, set to a proper value
> - * at boot time.
> - */
> -static unsigned int minimum_order __read_mostly = UINT_MAX;
> -
>  __initdata LIST_HEAD(huge_boot_pages);
>  
>  /* for command line parsing */
> @@ -2161,11 +2155,17 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
>  	unsigned long pfn;
>  	struct page *page;
>  	int rc = 0;
> +	unsigned int order;
> +	struct hstate *h;
>  
>  	if (!hugepages_supported())
>  		return rc;
>  
> -	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
> +	order = huge_page_order(&default_hstate);
> +	for_each_hstate(h)
> +		order = min(order, huge_page_order(h));
> +
> +	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order) {
>  		page = pfn_to_page(pfn);
>  		rc = dissolve_free_huge_page(page);
>  		if (rc)
> @@ -3157,9 +3157,6 @@ static void __init hugetlb_init_hstates(void)
>  	struct hstate *h, *h2;
>  
>  	for_each_hstate(h) {
> -		if (minimum_order > huge_page_order(h))
> -			minimum_order = huge_page_order(h);
> -
>  		/* oversize hugepages were init'ed in early boot */
>  		if (!hstate_is_gigantic(h))
>  			hugetlb_hstate_alloc_pages(h);
> @@ -3184,7 +3181,6 @@ static void __init hugetlb_init_hstates(void)
>  				h->demote_order = h2->order;
>  		}
>  	}
> -	VM_BUG_ON(minimum_order == UINT_MAX);
>  }
>  
>  static void __init report_hugepages(void)
> -- 
> 2.11.0
> 
> 

-- 
Oscar Salvador
SUSE Labs