linux-kernel - Re: [PATCH v2 1/2] mm/memory_hotplug: simplify calculation of number of pages in __remove

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Date:   Fri, 28 Feb 2020 18:22:54 +0800
From:   Baoquan He <bhe@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Wei Yang <richardw.yang@...ux.intel.com>
Subject: Re: [PATCH v2 1/2] mm/memory_hotplug: simplify calculation of number
 of pages in __remove_pages()

On 02/28/20 at 10:58am, David Hildenbrand wrote:
> In commit 52fb87c81f11 ("mm/memory_hotplug: cleanup __remove_pages()"),
> we cleaned up __remove_pages(), and introduced a shorter variant to
> calculate the number of pages to the next section boundary.
> 
> Turns out we can make this calculation easier to read. We always want to
> have the number of pages (> 0) to the next section boundary, starting from
> the current pfn.
> 
> We'll clean up __remove_pages() in a follow-up patch and directly make
> use of this computation.
> 
> Suggested-by: Segher Boessenkool <segher@...nel.crashing.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Wei Yang <richardw.yang@...ux.intel.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/memory_hotplug.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 4a9b3f6c6b37..8fe7e32dad48 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -534,7 +534,8 @@ void __remove_pages(unsigned long pfn, unsigned long nr_pages,
>  	for (; pfn < end_pfn; pfn += cur_nr_pages) {
>  		cond_resched();
>  		/* Select all remaining pages up to the next section boundary */
> -		cur_nr_pages = min(end_pfn - pfn, -(pfn | PAGE_SECTION_MASK));
> +		cur_nr_pages = min(end_pfn - pfn,
> +				   SECTION_ALIGN_UP(pfn + 1) - pfn);

Reviewed-by: Baoquan He <bhe@...hat.com>