Re: [PATCH v2 3/3] mm: return zero_resv_unavail optimization

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Tue, Sep 25, 2018 at 11:35:32AM -0400, Masayoshi Mizuma wrote:
> From: Pavel Tatashin <pavel.tatashin@microsoft.com>
> 
> When checking for valid pfns in zero_resv_unavail(), it is not necessary to
> verify that pfns within pageblock_nr_pages ranges are valid, only the first
> one needs to be checked. This is because memory for pages are allocated in
> contiguous chunks that contain pageblock_nr_pages struct pages.
> 
> Signed-off-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
> Reviewed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

According to convention, review tag is formatted like "Reviewed-by: ...",
Otherwise, looks good to me.

Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

> ---
>  mm/page_alloc.c | 46 ++++++++++++++++++++++++++--------------------
>  1 file changed, 26 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3b9d89e..bd5b7e4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6440,6 +6440,29 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
>  }
>  
>  #if defined(CONFIG_HAVE_MEMBLOCK) && !defined(CONFIG_FLAT_NODE_MEM_MAP)
> +
> +/*
> + * Zero all valid struct pages in range [spfn, epfn), return number of struct
> + * pages zeroed
> + */
> +static u64 zero_pfn_range(unsigned long spfn, unsigned long epfn)
> +{
> +	unsigned long pfn;
> +	u64 pgcnt = 0;
> +
> +	for (pfn = spfn; pfn < epfn; pfn++) {
> +		if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
> +			pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
> +				+ pageblock_nr_pages - 1;
> +			continue;
> +		}
> +		mm_zero_struct_page(pfn_to_page(pfn));
> +		pgcnt++;
> +	}
> +
> +	return pgcnt;
> +}
> +
>  /*
>   * Only struct pages that are backed by physical memory are zeroed and
>   * initialized by going through __init_single_page(). But, there are some
> @@ -6455,7 +6478,6 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
>  void __init zero_resv_unavail(void)
>  {
>  	phys_addr_t start, end;
> -	unsigned long pfn;
>  	u64 i, pgcnt;
>  	phys_addr_t next = 0;
>  
> @@ -6465,34 +6487,18 @@ void __init zero_resv_unavail(void)
>  	pgcnt = 0;
>  	for_each_mem_range(i, &memblock.memory, NULL,
>  			NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) {
> -		if (next < start) {
> -			for (pfn = PFN_DOWN(next); pfn < PFN_UP(start); pfn++) {
> -				if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
> -					continue;
> -				mm_zero_struct_page(pfn_to_page(pfn));
> -				pgcnt++;
> -			}
> -		}
> +		if (next < start)
> +			pgcnt += zero_pfn_range(PFN_DOWN(next), PFN_UP(start));
>  		next = end;
>  	}
> -	for (pfn = PFN_DOWN(next); pfn < max_pfn; pfn++) {
> -		if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
> -			continue;
> -		mm_zero_struct_page(pfn_to_page(pfn));
> -		pgcnt++;
> -	}
> -
> +	pgcnt += zero_pfn_range(PFN_DOWN(next), max_pfn);
>  
>  	/*
>  	 * Struct pages that do not have backing memory. This could be because
>  	 * firmware is using some of this memory, or for some other reasons.
> -	 * Once memblock is changed so such behaviour is not allowed: i.e.
> -	 * list of "reserved" memory must be a subset of list of "memory", then
> -	 * this code can be removed.
>  	 */
>  	if (pgcnt)
>  		pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
> -
>  }
>  #endif /* CONFIG_HAVE_MEMBLOCK && !CONFIG_FLAT_NODE_MEM_MAP */
>  
> -- 
> 2.18.0
> 
>