linux-kernel - Re: [PATCH] kexec: use Crash kernel for Crash kernel low

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Message-ID: <CAE9FiQX6Ay8rPNVVDLThCJ+ML40tS26w-51As7C9pmse6bpL8A@mail.gmail.com>
Date:	Tue, 2 Apr 2013 07:50:43 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, WANG Chao <chaowang@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kexec: use Crash kernel for Crash kernel low

On Tue, Apr 2, 2013 at 7:17 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Tue, Apr 02, 2013 at 09:50:01AM -0400, Vivek Goyal wrote:
>
> [..]
>> To achieve the behavior where we want to enforce that memory either
>> comes from low or high area only otherwise allocation fails, we could
>> probably use.
>>
>> crashkernel=X,high_only
>> crashkernel=X,low_only
>
> Thinking more about it. We have following existing syntax.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
>
> Which uses ',' as delimiter for range:size pairs.
>
> May be we can use a different delimiter, say ';'.
>
> crashkernel=<amount_of_memory_to_reserve>;<option1>;<option2>
>
> All the existing crashkernel= options should fall into the category of
> <amount_of_memory_to_reserve>.
>
> option1 could specify whether to search for memory from higher addresses
> or from lower addresses. (valid values are high or low)
>
> option2 could specify the range of memory search should be performed in.
> syntax to specify range could be XM:[YM]. So one could possibly specify.
>
> 4G-8G
> <4G
>>4G:<8G
>>8G
>
> Now crashkernel_low=0 could be emulated by
>
> crashkernel=0M;;<4G
>
> If we want to reserve 128MB of memory between 4G and 8G and starting scan
> from high, we could say.
>
> crashkernel=128M;high;>4G:<8G
>
> If this is deemed too generic and not worth it. Then we could simplify
> option 2 to take values "high_only" and "low_only" and that leaves the
> scope of implementing proper ranges down the line if need be.
>
> So crashkernel_low=0 will be emulated by.
>
> crashkernel=0M;;low_only

Oh, no. the grammar for crashkernel= looks crazy now.

You should not burden user like this.

Thanks

Yinghai
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