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

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Date:	Mon, 2 Sep 2013 11:41:44 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.com>
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().

On Mon, Sep 2, 2013 at 3:30 AM, Tang Chen <tangchen@...fujitsu.com> wrote:
> In current kernel, we update min_pfn_mapped and max_pfn_mapped like this:
>
> init_mem_mapping()
> {
>         while ( a loop iterates all memory ranges ) {
>                 init_range_memory_mapping();
>                  |->init_memory_mapping()
>                      |->kernel_physical_mapping_init()
>                      |->add_pfn_range_mapped()
>                          |-> update max_pfn_mapped;
>
>                 update min_pfn_mapped;
>         }
> }
>
> max_pfn_mapped is updated in add_pfn_range_mapped() when a range of memory
> is mapped. But min_pfn_mapped is updated in init_mem_mapping(). We can also
> update min_pfn_mapped in add_pfn_range_mapped().
>
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
>  arch/x86/mm/init.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 5b2eaca..a97749f 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -313,6 +313,7 @@ static void add_pfn_range_mapped(unsigned long start_pfn, unsigned long end_pfn)
>         nr_pfn_mapped = clean_sort_range(pfn_mapped, E820_X_MAX);
>
>         max_pfn_mapped = max(max_pfn_mapped, end_pfn);
> +       min_pfn_mapped = min(min_pfn_mapped, start_pfn);
>  }
>
>  bool pfn_range_is_mapped(unsigned long start_pfn, unsigned long end_pfn)
> @@ -442,7 +443,6 @@ void __init init_mem_mapping(void)
>                 new_mapped_ram_size = init_range_memory_mapping(start,
>                                                         last_start);
>                 last_start = start;
> -               min_pfn_mapped = last_start >> PAGE_SHIFT;
>                 /* only increase step_size after big range get mapped */
>                 if (new_mapped_ram_size > mapped_ram_size)
>                         step_size <<= STEP_SIZE_SHIFT;


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.

Yinghai
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