linux-kernel - Re: [PATCH v3 7/7] mm/sparse.c: Use __get_free_pages() instead in populate_section

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Message-ID: <20200310145647.GN8447@dhcp22.suse.cz>
Date:   Tue, 10 Mar 2020 15:56:47 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, david@...hat.com,
        richardw.yang@...ux.intel.com, dan.j.williams@...el.com,
        osalvador@...e.de, rppt@...ux.ibm.com
Subject: Re: [PATCH v3 7/7] mm/sparse.c: Use __get_free_pages() instead in
 populate_section_memmap()

On Sat 07-03-20 16:42:29, Baoquan He wrote:
> This removes the unnecessary goto, and simplify codes.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> Reviewed-by: Wei Yang <richardw.yang@...ux.intel.com>
> ---
>  mm/sparse.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index fde651ab8741..266f7f5040fb 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -735,23 +735,19 @@ static void free_map_bootmem(struct page *memmap)
>  struct page * __meminit populate_section_memmap(unsigned long pfn,
>  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
>  {
> -	struct page *page, *ret;
> +	struct page *ret;
>  	unsigned long memmap_size = sizeof(struct page) * PAGES_PER_SECTION;
>  
> -	page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
> -	if (page)
> -		goto got_map_page;
> +	ret = (void*)__get_free_pages(GFP_KERNEL|__GFP_NOWARN,
> +				get_order(memmap_size));
> +	if (ret)
> +		return ret;
>  
>  	ret = vmalloc(memmap_size);
>  	if (ret)
> -		goto got_map_ptr;
> +		return ret;
>  
>  	return NULL;
> -got_map_page:
> -	ret = (struct page *)pfn_to_kaddr(page_to_pfn(page));
> -got_map_ptr:
> -
> -	return ret;
>  }

Boy this code is ugly. Is there any reason we cannot simply use
kvmalloc_array(PAGES_PER_SECTION, sizeof(struct page), GFP_KERNEL | __GFP_NOWARN)

And if we care about locality then go even one step further
kvmalloc_node(PAGES_PER_SECTION * sizeof(struct page), GFP_KERNEL | __GFP_NOWARN, nid)

-- 
Michal Hocko
SUSE Labs