linux-kernel - Re: [PATCH RESEND 2/3] x86, mm: Update min_pfn_mapped in add_pfn_range

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Date:	Tue, 03 Sep 2013 09:06:15 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH RESEND 2/3] x86, mm: Update min_pfn_mapped in add_pfn_range_mapped().

Hi Yinghai,

On 09/03/2013 02:41 AM, Yinghai Lu wrote:
......
>
> Nak, you can not move that.
>
> min_pfn_mapped should not be updated before init_range_memory_mapping
> is returned. as it need to refer old min_pfn_mapped.
> and init_range_memory_mapping still init mapping from low to high locally.
> min_pfn_mapped can not be updated too early.

The current code is like this:

init_mem_mapping()
{
	while (from high to low) {
		init_range_memory_mapping()
		{
			/* Here is from low to high */
			for (from low to high) {
				init_memory_mapping()
				{
					for () {
						/* Need to refer min_pfn_mapped here */
						kernel_physical_mapping_init();
					}
					/* So if updating min_pfn_mapped here, it is too low */
					add_pfn_range_mapped();
				}
			}
		}		
	}
}

How about change the "for (from low to high)" in 
init_range_memory_mapping() to
"for_rev(from high to low)" ?
Then we can update min_pfn_mapped in add_pfn_range_mapped().

And also, the outer loop is from high to low, we can change the inner 
loop to be from high
to low too.

I think updating min_pfn_mapped in init_mem_mapping() is less readable. 
And min_pfn_mapped
and max_pfn_mapped should be updated together.

Thanks.

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