linux-kernel - Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement

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Message-ID: <20130321144929.GH3934@redhat.com>
Date:	Thu, 21 Mar 2013 10:49:29 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com,
	heiko.carstens@...ibm.com, akpm@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	zhangyanfei@...fujitsu.com
Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s
 page-size boundary requirement

On Thu, Mar 21, 2013 at 12:22:59AM -0700, Eric W. Biederman wrote:
> HATAYAMA Daisuke <d.hatayama@...fujitsu.com> writes:
> 
> > OK, rigorously, suceess or faliure of the requested free pages
> > allocation depends on actual memory layout at the 2nd kernel boot. To
> > increase the possibility of allocating memory, we have no method but
> > reserve more memory for the 2nd kernel now.
> 
> Good enough.   If there are fragmentation issues that cause allocation
> problems on larger boxes we can use vmalloc and remap_vmalloc_range, but
> we certainly don't need to start there.
> 
> Especialy as for most 8 or 16 core boxes we are talking about a 4KiB or
> an 8KiBP allocation.  Aka order 0 or order 1.
> 

Actually we are already handling the large SGI machines so we need
to plan for 4096 cpus now while we write these patches.

vmalloc() and remap_vmalloc_range() sounds reasonable. So that's what
we should probaly use.

Alternatively why not allocate everything in 4K pages and use vmcore_list
to map offset into right addresses and call remap_pfn_range() on these
addresses.

Thanks
Vivek
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