Message-ID: <5189DB4A.8020902@jp.fujitsu.com>
Date: Wed, 08 May 2013 13:57:46 +0900
From: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130328 Thunderbird/17.0.5
MIME-Version: 1.0
To: Vivek Goyal <vgoyal@redhat.com>
CC: kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        lisa.mitchell@hp.com, kumagai-atsushi@mxc.nes.nec.co.jp,
        ebiederm@xmission.com, zhangyanfei@cn.fujitsu.com,
        akpm@linux-foundation.org, cpw@sgi.com, jingbai.ma@hp.com
Subject: Re: [PATCH v4 5/8] vmcore: copy ELF note segments in the 2nd kernel
 per page vmcore objects
References: <20130413002000.18245.21513.stgit@localhost6.localdomain6> <20130413002133.18245.91528.stgit@localhost6.localdomain6> <20130429193611.GQ8204@redhat.com> <5188B3BE.9040104@jp.fujitsu.com> <20130507150840.GA12965@redhat.com>
In-Reply-To: <20130507150840.GA12965@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2005
Lines: 45

(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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/