Re: [PATCH v2] makedumpfile: request the kernel do page scans

HATAYAMA Daisuke
2013-01-09T15:12:08Z

Subject: Re: [PATCH v2] makedumpfile: request the kernel do page scans
Date: Mon, 7 Jan 2013 07:39:35 -0600

> An update on testing thise patches:
>
>> This version of the patch improves the consolidation of the mem_map table
>> that is passed to the kernel. See make_kernel_mmap().
>> Particularly the seemingly duplicate pfn ranges generated on an older
>> (2.6.32-based, rhel6) kernel.
>
>
> On a 2TB machine (idle) machine:
> the crash kernel ran successfully in 512M
> the scan for unnecessary pages takes about 40 seconds
> it was a single scan, not cyclic
>
> On a 16TB machine (idle) machine:
> the crash kernel ran successfully in 512M
> there is a pause of about 4 minutes during makedumpfile initialization
> the scan for unnecessary pages takes about 4.8 minutes
> it was a single scan, not cyclic
>

I wonder why this didn't result in OOM on 16TB. Was that really done
in non-cyclic mode? Could you show me a log of makedumpfile? You can
create it by passing --message-level 31.

Also, to consider how to resolve this performance issue, this test is
not enough. We also need to benchmark that *without filtering in
kernel-space* but with making page tables, not using ioremap. As I
said before, I think the bad performance is caused by too many calls
of ioremap/iounmap. We then need to comapre two results of these
benchmarks.

Thanks.
HATAYAMA, Daisuke