linux-kernel - Re: [PATCH] kdump x86: fix total mem size calculation for reservation

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Date:	Sat, 10 Mar 2012 11:27:41 +0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Dave Young <dyoung@...hat.com>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux@....linux.org.uk, vgoyal@...hat.com
Subject: Re: [PATCH] kdump x86: fix total mem size calculation for reservation

On 03/09/2012 04:30 PM, Dave Young wrote:
> crashkernel reservation need know the total memory size. Current get_total_mem
> simply use max_pfn - min_low_pfn. It is wrong because it will including
> memory holes in the middle.
>
> Especially for kvm guest with memory>  0xe0000000, there's below in qemu code:
> qemu split memory as below:
>      if (ram_size>= 0xe0000000 ) {
>          above_4g_mem_size = ram_size - 0xe0000000;
>          below_4g_mem_size = 0xe0000000;
>      } else {
>          below_4g_mem_size = ram_size;
>      }
> So for 4G mem guest, seabios will insert a 512M usable region beyond of 4G.
> Thus in above case max_pfn - min_low_pfn will be more than original memsize.
>
> Fixing this issue by using memblock_phys_mem_size() to get the total memsize.
>

Makes sense for me!

> -static inline unsigned long long get_total_mem(void)
> -{
> -	unsigned long long total;
> -
> -	total = max_pfn - min_low_pfn;
> -	printk("hidave: memsize=%llu\n", memblock_phys_mem_size());

This debugging line does not exist... so this patch can't be applied.
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