linux-kernel - Re: [RFC 2/4] Have __free_pages_memory() free in larger chunks.

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Date:	Tue, 16 Jul 2013 21:02:53 +0800
From:	Sam Ben <sam.bennn@...il.com>
To:	Robin Holt <holt@....com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Nate Zimmer <nzimmer@....com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>, Rob Landley <rob@...dley.net>,
	Mike Travis <travis@....com>,
	Daniel J Blueman <daniel@...ascale-asia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Yinghai Lu <yinghai@...nel.org>, Mel Gorman <mgorman@...e.de>
Subject: Re: [RFC 2/4] Have __free_pages_memory() free in larger chunks.

Hi Robin,
On 07/12/2013 10:03 AM, Robin Holt wrote:
> Currently, when free_all_bootmem() calls __free_pages_memory(), the
> number of contiguous pages that __free_pages_memory() passes to the
> buddy allocator is limited to BITS_PER_LONG.  In order to be able to

I fail to understand this. Why the original page number is BITS_PER_LONG?

> free only the first page of a 2MiB chunk, we need that to be increased
> to PTRS_PER_PMD.
>
> Signed-off-by: Robin Holt <holt@....com>
> Signed-off-by: Nate Zimmer <nzimmer@....com>
> To: "H. Peter Anvin" <hpa@...or.com>
> To: Ingo Molnar <mingo@...nel.org>
> Cc: Linux Kernel <linux-kernel@...r.kernel.org>
> Cc: Linux MM <linux-mm@...ck.org>
> Cc: Rob Landley <rob@...dley.net>
> Cc: Mike Travis <travis@....com>
> Cc: Daniel J Blueman <daniel@...ascale-asia.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Cc: Mel Gorman <mgorman@...e.de>
> ---
>   mm/nobootmem.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/nobootmem.c b/mm/nobootmem.c
> index bdd3fa2..3b512ca 100644
> --- a/mm/nobootmem.c
> +++ b/mm/nobootmem.c
> @@ -83,10 +83,10 @@ void __init free_bootmem_late(unsigned long addr, unsigned long size)
>   static void __init __free_pages_memory(unsigned long start, unsigned long end)
>   {
>   	unsigned long i, start_aligned, end_aligned;
> -	int order = ilog2(BITS_PER_LONG);
> +	int order = ilog2(max(BITS_PER_LONG, PTRS_PER_PMD));
>   
> -	start_aligned = (start + (BITS_PER_LONG - 1)) & ~(BITS_PER_LONG - 1);
> -	end_aligned = end & ~(BITS_PER_LONG - 1);
> +	start_aligned = (start + ((1UL << order) - 1)) & ~((1UL << order) - 1);
> +	end_aligned = end & ~((1UL << order) - 1);
>   
>   	if (end_aligned <= start_aligned) {
>   		for (i = start; i < end; i++)
> @@ -98,7 +98,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
>   	for (i = start; i < start_aligned; i++)
>   		__free_pages_bootmem(pfn_to_page(i), 0);
>   
> -	for (i = start_aligned; i < end_aligned; i += BITS_PER_LONG)
> +	for (i = start_aligned; i < end_aligned; i += 1 << order)
>   		__free_pages_bootmem(pfn_to_page(i), order);
>   
>   	for (i = end_aligned; i < end; i++)

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