linux-kernel - Re: [PATCH v2] kdump x86: fix total mem size calculation for reservation

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Message-ID: <CABqxG0e5MbkLs=YfbGqirkeD-mLPN8-N1gNyG4WR_EqQjadXpw@mail.gmail.com>
Date:	Sun, 11 Mar 2012 00:06:47 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux@....linux.org.uk, vgoyal@...hat.com
Subject: Re: [PATCH v2] kdump x86: fix total mem size calculation for reservation

On Sat, Mar 10, 2012 at 4:38 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On 03/10/2012 12:56 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.
>>
>> [v1 ->  v2]: refresh the patch based on latest linus tree
>>
>
> Looks good to my eyes,
>
> Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>
>
> Can you post the result of crashkernel after this patch to convince people?

Sure, for the qemu  4G vm results below:
-[    0.000000] Reserving 128MB of memory at 768MB for crashkernel
(System RAM: 4608MB)
+[    0.000000] Reserving 128MB of memory at 768MB for crashkernel
(System RAM: 4095MB)

>
> Thanks.
>
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-- 
Regards
Dave
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