Re: [PATCH 3/3] x86, crash: Allocate enough low-mem when crashkernel=high

From: Baoquan He <bhe@redhat.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Joerg Roedel <jroedel@suse.de>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] x86, crash: Allocate enough low-mem when crashkernel=high
Date: Fri, 13 Feb 2015 23:34:38 +0800	[thread overview]
Message-ID: <20150213153438.GA4483@dhcp-17-102.nay.redhat.com> (raw)
In-Reply-To: <20150209122042.GA29106@8bytes.org>

On 02/09/15 at 01:20pm, Joerg Roedel wrote:
> Hi Baoquan,
> 
> On Wed, Feb 04, 2015 at 03:10:20PM +0100, Joerg Roedel wrote:
> > That makes sense. I also asked the customer to test intermediate values,
> > we already know that it works with 256MB but also that 128MB are not
> > enough. I will report back when I have the results of the intermediate
> > values in 32MB steps.
> 
> I got the results from the customer, and it turns out that a value of
> 192MB is sufficient to make the kdump succeed. It fails with 128MB and
> 160MB. 
> 
> So I think we can settle in 192MB for now. What do you think?

Hi Joerg,

Sorry for late reply.

So that machine need eat memory between 160M and 192M. Then how about
setting it as 256M? Since 192M seems very close to the brink, and
setting it larger can keep enough space to extend for increasing dma
device on larger machines, otherwise this value could be increased soon.

Wasting some low memory is better than kdump kernel can't bootup
caused by not enough low memory. If someone grudge the low mem they can
specify crashkernel=size,low manually.

Conclusively, I like 256M since the testing data showed it's sufficient
now and should be save for a long time.

Thanks
Baoquan