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

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Message-ID: <20130712074558.GP18798@sgi.com>
Date:	Fri, 12 Jul 2013 02:45:58 -0500
From:	Robin Holt <holt@....com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
Cc:	Robin Holt <holt@....com>, 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.

After sleeping on this, why can't we change __free_pages_bootmem
to not take an order, but rather nr_pages?  If we did that,
then __free_pages_memory could just calculate nr_pages and call
__free_pages_bootmem one time.

I don't see why any of the callers of __free_pages_bootmem would not
easily support that change.  Maybe I will work that up as part of a -v2
and see if it boots/runs.

At the very least, I think we could change to:
static void __init __free_pages_memory(unsigned long start, unsigned long end)
{
	int order;

	while (start < end) {
		order = ffs(start);

		while (start + (1UL << order) > end)
			order--;

		__free_pages_bootmem(start, order);

		start += (1UL << order);
	}
}


Robin

On Thu, Jul 11, 2013 at 09:03:53PM -0500, 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
> 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++)
> -- 
> 1.8.2.1
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