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: <20130507150840.GA12965@redhat.com>
Date:	Tue, 7 May 2013 11:08:40 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.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

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.

Thanks
Vivek
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