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

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Message-ID: <20150722101133.GH10969@8bytes.org>
Date:	Wed, 22 Jul 2015 12:11:33 +0200
From:	Joerg Roedel <joro@...tes.org>
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 Tue, Jul 21, 2015 at 12:22:53PM -0700, 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.

All Intel-IOMMU systems have the iommu disabled by default (at least
that is the default in most distros). So low memory is definitly needed
by those systems too.

> 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.

We currently lack the infrastructure for that, but I am happy to review
patches. How about letting subsystems announce their need for low
crash-kernel memory and allocate based on that?

The subsystems (like iommu or swiotlb code, for example) could even
announce how much memory they need and we base our allocation on that.


	Joerg

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