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

[Jingbai Ma]

On 03/08/2013 11:52 PM, Vivek Goyal wrote:
> On Thu, Mar 07, 2013 at 01:54:45PM -0800, Eric W. Biederman wrote:
> > Vivek Goyal<vgoyal@xxxxxxxxxx>  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. :-)

I was thought this function code is pretty simple, could be called here 
safely.
If it's not proper for here, how about before the function 
machine_crash_shutdown(&fixed_regs)?
Furthermore, could you explain the real risks to execute more codes here?

Thanks!

> Thanks
> Vivek


--
Jingbai Ma (jingbai.ma@xxxxxx)
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