linux-kernel - Re: [PATCH v2 1/4] mm: change type of free_contig_range(nr

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Date:   Fri, 18 May 2018 11:12:54 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Guy Shattah <sguy@...lanox.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        David Nellans <dnellans@...dia.com>,
        Laura Abbott <labbott@...hat.com>, Pavel Machek <pavel@....cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 1/4] mm: change type of free_contig_range(nr_pages) to
 unsigned long

On 05/04/2018 01:29 AM, Mike Kravetz wrote:
> free_contig_range() is currently defined as:
> void free_contig_range(unsigned long pfn, unsigned nr_pages);
> change to,
> void free_contig_range(unsigned long pfn, unsigned long nr_pages);
> 
> Some callers are passing a truncated unsigned long today.  It is
> highly unlikely that these values will overflow an unsigned int.
> However, this should be changed to an unsigned long to be consistent
> with other page counts.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
>  include/linux/gfp.h | 2 +-
>  mm/cma.c            | 2 +-
>  mm/hugetlb.c        | 2 +-
>  mm/page_alloc.c     | 6 +++---
>  4 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 1a4582b44d32..86a0d06463ab 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -572,7 +572,7 @@ static inline bool pm_suspended_storage(void)
>  /* The below functions must be run on a range from a single zone. */
>  extern int alloc_contig_range(unsigned long start, unsigned long end,
>  			      unsigned migratetype, gfp_t gfp_mask);
> -extern void free_contig_range(unsigned long pfn, unsigned nr_pages);
> +extern void free_contig_range(unsigned long pfn, unsigned long nr_pages);
>  #endif
>  
>  #ifdef CONFIG_CMA
> diff --git a/mm/cma.c b/mm/cma.c
> index aa40e6c7b042..f473fc2b7cbd 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -563,7 +563,7 @@ bool cma_release(struct cma *cma, const struct page *pages, unsigned int count)
>  
>  	VM_BUG_ON(pfn + count > cma->base_pfn + cma->count);
>  
> -	free_contig_range(pfn, count);
> +	free_contig_range(pfn, (unsigned long)count);

I guess this cast from uint to ulong doesn't need to be explicit? But
instead, cma_release() signature could be also changed to ulong, because
some of its callers do pass those?

>  	cma_clear_bitmap(cma, pfn, count);
>  	trace_cma_release(pfn, pages, count);
>  
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 218679138255..c81072ce7510 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1055,7 +1055,7 @@ static void destroy_compound_gigantic_page(struct page *page,
>  
>  static void free_gigantic_page(struct page *page, unsigned int order)
>  {
> -	free_contig_range(page_to_pfn(page), 1 << order);
> +	free_contig_range(page_to_pfn(page), 1UL << order);
>  }
>  
>  static int __alloc_gigantic_page(unsigned long start_pfn,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 905db9d7962f..0fd5e8e2456e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7937,9 +7937,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>  	return ret;
>  }
>  
> -void free_contig_range(unsigned long pfn, unsigned nr_pages)
> +void free_contig_range(unsigned long pfn, unsigned long nr_pages)
>  {
> -	unsigned int count = 0;
> +	unsigned long count = 0;
>  
>  	for (; nr_pages--; pfn++) {
>  		struct page *page = pfn_to_page(pfn);
> @@ -7947,7 +7947,7 @@ void free_contig_range(unsigned long pfn, unsigned nr_pages)
>  		count += page_count(page) != 1;
>  		__free_page(page);
>  	}
> -	WARN(count != 0, "%d pages are still in use!\n", count);
> +	WARN(count != 0, "%ld pages are still in use!\n", count);

Maybe change to %lu while at it?
BTW, this warning can theoretically produce false positives, because
page users have to deal with page_count() being incremented by e.g.
parallel pfn scanners using get_page_unless_zero(). We also don't detect
refcount leaks in general. Should we remove it or change it to VM_WARN
if it's still useful for debugging?

>  }
>  #endif
>  
>