linux-kernel - Re: [RFC PATCH 0/5] crash dump bitmap: scan memory pages in kernel to speedup kernel dump process

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Date:	Fri, 8 Mar 2013 10:52:16 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Jingbai Ma <jingbai.ma@...com>, mingo@...hat.com,
	kumagai-atsushi@....nes.nec.co.jp, hpa@...or.com,
	yinghai@...nel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/5] crash dump bitmap: scan memory pages in kernel
 to speedup kernel dump process

On Thu, Mar 07, 2013 at 01:54:45PM -0800, Eric W. Biederman wrote:
> Vivek Goyal <vgoyal@...hat.com> writes:
> 
> > On Thu, Mar 07, 2013 at 10:58:18PM +0800, Jingbai Ma wrote:
> >> This patch intend to speedup the memory pages scanning process in
> >> selective dump mode.
> >> 
> >> Test result (On HP ProLiant DL980 G7 with 1TB RAM, makedumpfile
> >> v1.5.3):
> >> 
> >> 						Total scan Time
> >> Original kernel
> >> 	+ makedumpfile v1.5.3 cyclic mode	1958.05 seconds
> >> Original kernel
> >> 	+ makedumpfile v1.5.3 non-cyclic mode	1151.50 seconds
> >> Patched kernel
> >> 	+ patched makedumpfile v1.5.3		17.50 seconds
> >> 
> >> Traditionally, to reduce the size of dump file, dumper scans all memory
> >> pages to exclude the unnecessary memory pages after capture kernel
> >> booted, and scan it in userspace code (makedumpfile).
> >
> > I think this is not a good idea. It has several issues.
> 
> Actually it does not appear to be doing any work in the first kernel.

Looks like patch3 in series is doing that.

                        machine_crash_shutdown(&fixed_regs);
+                       generate_crash_dump_bitmap();
                        machine_kexec(kexec_crash_image);

So this bitmap seems to be being set just before transitioning into
second kernel.

I am sure you would not like this extra code in this path. :-)

Thanks
Vivek
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