makedumpfile 1.5.0 takes much more time to dump

[HATAYAMA Daisuke]

From: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
Subject: Re: makedumpfile 1.5.0 takes much more time to dump
Date: Fri, 21 Sep 2012 09:23:57 +0900

> From: Vivek Goyal <vgoyal at redhat.com>
> Subject: makedumpfile 1.5.0 takes much more time to dump
> Date: Thu, 20 Sep 2012 16:06:34 -0400
> 
>> Hi Atsushi san,
>> 
>> We tried makedumpfile 1.5.0 on a 1TB machine and it seems to regress
>> badly. We reserved 192MB of memory and following are test results.
>> 
>> #1. makedumpfile-1.4.2 -E --message-level 1 -d 31
>> real     3m47.520s
>> user     0m56.543s
>> sys	 2m41.631s
>> 
>> #2. makedumpfile-1.5.0 -E --message-level 1 -d 31
>> real     52m25.262s
>> user     32m51.310s
>> sys	 18m53.265s
>> 
>> #3. makedumpfile-1.4.2 -c --message-level 1 -d 31
>> real     8m49.107s
>> user     4m34.180s
>> sys	 4m8.691s
>> 
>> #4. makedumpfile-1.5.0 -c --message-level 1 -d 31
>> real     46m48.985s
>> user     29m35.203s
>> sys	 16m43.149s
>> 
> 
> Hello Vivek,
> 
> On v1.5.0 we cannot filter free pages in constant space becuase we
> have yet to test it. Instead, the existing method is used here, which
> repeats walking on a whole page frames the number of cycles times.
> 
> As Kumagai-san explains, the number of cycles can be calculated by the
> following expression:
> 
>   N = physical memory size / (page size * bit per byte(8) * BUFSIZE_CYCLIC)
> 
> So,
> 
>   N = 2TB / (4KB * 8 * 1MB) = 64 cycles.
> 
> I guess on this environment, it took about 50 seconds to filter free
> pages in one cycle.
> 

I noticed a careless miss. 1TB is correct on your case.

   N = 1TB / (4KB * 8 * 1MB) = 32 cycles.

So, about 95 seconds for one cycle?

Thanks.
HATAYAMA, Daisuke