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

[HATAYAMA Daisuke]

From: Vivek Goyal <vgoyal at redhat.com>
Subject: Re: [RFC PATCH 0/5] crash dump bitmap: scan memory pages in kernel to speedup kernel dump process
Date: Thu, 7 Mar 2013 10:21:08 -0500

> On Thu, Mar 07, 2013 at 10:58:18PM +0800, Jingbai Ma wrote:
<cut>
>> 
>> 2. Scans all memory pages in makedumpfile is a very slow process. On
>> system with 1TB or more memory installed, the scanning process is very
>> long. Typically on 1TB idle system, it takes about 19 minutes. On system
>> with 4TB or more memory installed, it even doesn't work. To address the
>> out of memory issue on system with big memory (4TB or more memory
>> installed),  makedumpfile v1.5.1 introduces a new cyclic mode. It only
>> scans a piece of memory pages each time, and do it cyclically to scan
>> all memory pages. But it runs more slowly, on 1TB system, takes about 33
>> minutes.
> 
> One of the reasons it is slow because we don't support mmpa() interface.
> That means for every read, we map 4K page, flush TLB, read it, unmap it
> and flush TLB again. This is lot of processing overhead per 4K page.
> 
> Hatayama is now working on making mmap() interface and allow user space
> to bigger chunks of memory in one so. So that in one mmap() call we can
> map a bigger range instead of just 4K. And his numbers show that it
> has helped a lot.

Yes, so when are you able to get down to reviewing the patch set?

Thanks.
HATAYAMA, Daisuke