Re: [PATCH] [RFC] mm/mm_init.c: simplify logic of deferred_[init|free]_pages

[Mike Rapoport <rppt@kernel.org>]

On Wed, Jun 05, 2024 at 01:07:42AM +0000, Wei Yang wrote:
> Function deferred_[init|free]_pages are only used in
> deferred_init_maxorder(), which makes sure the range to init/free is
> within MAX_ORDER_NR_PAGES size.
> 
> With this knowledge, we can simplify these two functions. Since
> 
>   * only the first pfn could be IS_MAX_ORDER_ALIGNED()

No, the first pfn is not necessarily IS_MAX_ORDER_ALIGNED(). Start pfn is a
beginning of a region in memblock.memory, and there's no guarantee on it's
alignment.
 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> CC: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> CC: Mike Rapoport (IBM) <rppt@kernel.org>
> CC: David Hildenbrand <david@redhat.com>
> 
> ---
> But my question is why we just test pfn_valid for the
> IS_MAX_ORDER_ALIGNED pfn? I thought we should test pfn_valid for each
> pfn until the first one in MAX_ORDER pages. Do I miss something?
> ---
>  mm/mm_init.c | 43 ++++++++++++++-----------------------------
>  1 file changed, 14 insertions(+), 29 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index bbaf3a2c1cfd..6a4adf9e7d9a 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1970,21 +1970,10 @@ static inline bool __init deferred_pfn_valid(unsigned long pfn)
>  static void __init deferred_free_pages(unsigned long pfn,
>  				       unsigned long end_pfn)
>  {
> -	unsigned long nr_free = 0;
> -
> -	for (; pfn < end_pfn; pfn++) {
> -		if (!deferred_pfn_valid(pfn)) {
> -			deferred_free_range(pfn - nr_free, nr_free);
> -			nr_free = 0;
> -		} else if (IS_MAX_ORDER_ALIGNED(pfn)) {
> -			deferred_free_range(pfn - nr_free, nr_free);
> -			nr_free = 1;
> -		} else {
> -			nr_free++;
> -		}
> -	}
> -	/* Free the last block of pages to allocator */
> -	deferred_free_range(pfn - nr_free, nr_free);
> +	if (!deferred_pfn_valid(pfn))
> +		pfn++;
> +
> +	deferred_free_range(pfn, end_pfn - pfn);
>  }
>  
>  /*
> @@ -1992,27 +1981,23 @@ static void __init deferred_free_pages(unsigned long pfn,
>   * by performing it only once every MAX_ORDER_NR_PAGES.
>   * Return number of pages initialized.
>   */
> -static unsigned long  __init deferred_init_pages(struct zone *zone,
> -						 unsigned long pfn,
> -						 unsigned long end_pfn)
> +static unsigned long __init deferred_init_pages(struct zone *zone,
> +						unsigned long pfn,
> +						unsigned long end_pfn)
>  {
>  	int nid = zone_to_nid(zone);
>  	unsigned long nr_pages = 0;
>  	int zid = zone_idx(zone);
>  	struct page *page = NULL;
>  
> -	for (; pfn < end_pfn; pfn++) {
> -		if (!deferred_pfn_valid(pfn)) {
> -			page = NULL;
> -			continue;
> -		} else if (!page || IS_MAX_ORDER_ALIGNED(pfn)) {
> -			page = pfn_to_page(pfn);
> -		} else {
> -			page++;
> -		}
> +	if (!deferred_pfn_valid(pfn))
> +		pfn++;
> +
> +	page = pfn_to_page(pfn);
> +	nr_pages = end_pfn - pfn;
> +
> +	for (; pfn < end_pfn; pfn++, page++)
>  		__init_single_page(page, pfn, zid, nid);
> -		nr_pages++;
> -	}
>  	return nr_pages;
>  }
>  
> -- 
> 2.34.1
> 

-- 
Sincerely yours,
Mike.