linux-kernel - Re: [PATCH] mm: Introduce kernelcore=reliable option

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Message-ID: <5628B427.3050403@jp.fujitsu.com>
Date:	Thu, 22 Oct 2015 19:02:15 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Luck, Tony" <tony.luck@...el.com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Cc:	"qiuxishi@...wei.com" <qiuxishi@...wei.com>,
	"mel@....ul.ie" <mel@....ul.ie>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] mm: Introduce kernelcore=reliable option

On 2015/10/22 3:17, Luck, Tony wrote:
> +	if (reliable_kernelcore) {
> +		for_each_memblock(memory, r) {
> +			if (memblock_is_mirror(r))
> +				continue;
>
> Should we have a safety check here that there is some mirrored memory?  If you give
> the kernelcore=reliable option on a machine which doesn't have any mirror configured,
> then we'll mark all memory as removable.

You're right.

> What happens then?  Do kernel allocations fail?  Or do they fall back to using removable memory?

Maybe the kernel cannot boot because NORMAL zone is empty.

> Is there a /proc or /sys file that shows the current counts for the removable zone?  I just
> tried this patch with a high percentage of memory marked as mirror ... but I'd like to see
> how much is actually being used to tune things a bit.
>

I think /proc/zoneinfo can show detailed numbers per zone. Do we need some for meminfo ?

Thanks,
-Kame


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