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 08:59:30 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	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.

Yeah, you are right.

> 
> 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.

Those big servers mostly has hardware iommu. But they still can
enable swiotlb suport. Then low memory is needed.

> 
> Yinghai
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