linux-kernel - Re: [PATCH v4 5/8] vmcore: copy ELF note segments in the 2nd kernel per page vmcore objects

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Message-ID: <5189DB4A.8020902@jp.fujitsu.com>
Date:	Wed, 08 May 2013 13:57:46 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	lisa.mitchell@...com, kumagai-atsushi@....nes.nec.co.jp,
	ebiederm@...ssion.com, zhangyanfei@...fujitsu.com,
	akpm@...ux-foundation.org, cpw@....com, jingbai.ma@...com
Subject: Re: [PATCH v4 5/8] vmcore: copy ELF note segments in the 2nd kernel
 per page vmcore objects

(2013/05/08 0:08), Vivek Goyal wrote:
> On Tue, May 07, 2013 at 04:56:46PM +0900, HATAYAMA Daisuke wrote:
>> (2013/04/30 4:36), Vivek Goyal wrote:
>>> On Sat, Apr 13, 2013 at 09:21:33AM +0900, HATAYAMA Daisuke wrote:
>>>
>>> [..]
>>>> ELF notes are per-cpu, so total size of ELF note segments increases
>>>> according to the number of CPUs. The current maximum number of CPUs on
>>>> x86_64 is 5192, and there's already system with 4192 CPUs in SGI,
>>>> where total size amounts to 1MB. This can be larger in the neare
>>>> futrue or possibly even now on another architecture. Thus, to avoid
>>>> the case where memory allocation for large block fails, we allocate
>>>> vmcore objects per pages.
>>>
>>> IIRC, eric had suggested using vmalloc() and remap_vmalloc_range(). What's
>>> wrong with that? That should keep your vc_list relatively smaller.
>>>
>>
>> Yes, it's handy if it's possible to remap them in vmalloc space, but
>> the problem here is that remap_vmalloc_range requires the first
>> argument vma to cover full range of the requested map. This becomes
>> problem when requested area for mmap() overlaps multiple objects,
>> for example, ELF headers and memory refered to by the first PT_LOAD
>> program header.
>>
>> To use remap_vmalloc_range, it's necessary to prepare a new variant
>> similar to remap_pfn_range by which we can remap different objects
>> separately to a single vma.
>
> Ok. Is it hard to prepare one such variant. If we can write one, it will
> simplify the vmcore code.

I'll try to write it. Although I avoided implementing it once, now it 
looks relatively easy to implement thanks to vm_insert_page, which does 
all essential thing. All I have to do should be consider sanity-check only.

-- 
Thanks.
HATAYAMA, Daisuke

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