linux-kernel - Re: [PATCH v2] Do not reserve crashkernel high memory if crashkernel low memory reserving failed

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Date:	Wed, 22 Jul 2015 12:47:27 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Vivek Goyal <vgoyal@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Do not reserve crashkernel high memory if crashkernel
 low memory reserving failed

On 07/21/15 at 12:22pm, Yinghai Lu wrote:
> On Tue, Jul 21, 2015 at 1:58 AM, Baoquan He <bhe@...hat.com> wrote:
> 
> > Maybe system which don't need low memory is rare, only for testing?
> 
> No, it is not rare.
> 
> All recent intel based systems with iommu support does not need low.
> 
> And those systems get punished by following patch:
> 
> | commit 94fb9334182284e8e7e4bcb9125c25dc33af19d4
> | Author: Joerg Roedel <jroedel@...e.de>
> | Date:   Wed Jun 10 17:49:42 2015 +0200
> |
> |    x86/crash: Allocate enough low memory when crashkernel=high
> 
> that reserve 256M low always. and those 256M get wasted.
> 
> That commit should only be used to workaround some systems that
> have partial iommu support.
> 

Since low memory does not need for some machines, how about kexec does
not allocate low memory automatically, if cmdline does not specify the
option ",low". User shall know well, if they specify the cmdline with
option ",high".

Thanks
Minfei
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