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

[Dave Young]

On Sat, Mar 10, 2012 at 4:38 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> 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> Â0xe0000000, there's below in qemu
>> code:
>> qemu split memory as below:
>> Â Â if (ram_size>= 0xe0000000 ) {
>> Â Â Â Â above_4g_mem_size = ram_size - 0xe0000000;
>> Â Â Â Â below_4g_mem_size = 0xe0000000;
>> Â Â } else {
>> Â Â Â Â below_4g_mem_size = ram_size;
>> Â Â }
>> 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 -> Âv2]: refresh the patch based on latest linus tree
>>
>
> Looks good to my eyes,
>
> Reviewed-by: WANG Cong <xiyou.wangcong@xxxxxxxxx>
>
> 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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