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In-Reply-To: <200907031314.36243.lkml@morethan.org>
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Date: Fri, 3 Jul 2009 13:07:04 -0700
Message-ID: <86802c440907031307s43fca3c0j77d4df78450ff757@mail.gmail.com>
Subject: Re: [Bug Fix]: Do 32-bit table calculations in pre-processor
From: Yinghai Lu <yhlu.kernel@gmail.com>
To: lkml@morethan.org
Cc: linux-kernel@vger.kernel.org
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On Fri, Jul 3, 2009 at 11:14 AM, Michael S. Zick<lkml@morethan.org> wrote:
> Here is one I have found useful in my VIA processor bug hunting:
>
> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> index 3068388..2303d86 100644
> --- a/arch/x86/kernel/head_32.S
> +++ b/arch/x86/kernel/head_32.S
> @@ -61,7 +61,7 @@
>
> ?/* Enough space to fit pagetables for the low memory linear map */
> ?MAPPING_BEYOND_END = \
> - ? ? ? PAGE_TABLE_SIZE(((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT) << PAGE_SHIFT
> + ? ? ? PAGE_TABLE_SIZE((1<<20) - (__PAGE_OFFSET >> PAGE_SHIFT)) << PAGE_SHIFT
>
> ?/*
> ?* Worst-case size of the kernel mapping we need to make:
>
> = = =
>
> Before:
>
> ?#5 [0000010000 - 0000011000] ? ? ? ? ?PGTABLE ==> [0000010000 - 0000011000]
> ?#6 [0000011000 - 0000015000] ? ? ? ? ?BOOTMAP ==> [0000011000 - 0000015000]
>
> After:
>
> ?#5 [0000010000 - 000007d000] ? ? ? ? ?PGTABLE ==> [0000010000 - 000007d000]
> ?#6 [000007d000 - 0000081000] ? ? ? ? ?BOOTMAP ==> [000007d000 - 0000081000]
>

that PGTABLE is from early resource. and it is filled by init_memory_mapping()

it mean preallocated pgtable to MAPPING_BEYOND_END is small now after
patch. and init_memory_mapping try to get more.

please send out whole dmesg. with and without your patch. it could
print out initial mapped before e820 allocation is involved for 32bit
        printk(KERN_DEBUG "initial memory mapped : 0 - %08lx\n",
                        max_pfn_mapped<<PAGE_SHIFT);


your patch should be right. except to change that 12 to PAGE_SHIFT

YH
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