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

Jingbai Ma
2013-03-11T08:18:10Z

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@redhat.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. :-)

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@hp.com)