Re: Problem in Page Cache Replacement

metin d
2012-11-23T08:25:19Z

----- Original Message -----

From: Jaegeuk Hanse <jaegeuk.hanse@gmail.com>
To: metin d <metdos@yahoo.com>
Cc: Jan Kara <jack@suse.cz>; "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>; "linux-mm@kvack.org" <linux-mm@kvack.org>
Sent: Friday, November 23, 2012 10:17 AM
Subject: Re: Problem in Page Cache Replacement

On 11/23/2012 04:08 PM, metin d wrote:
> ----- Original Message -----
>
> From: Jaegeuk Hanse <jaegeuk.hanse@gmail.com>
> To: metin d <metdos@yahoo.com>
> Cc: Jan Kara <jack@suse.cz>; "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>; linux-mm@kvack.org
> Sent: Friday, November 23, 2012 3:58 AM
> Subject: Re: Problem in Page Cache Replacement
>
> On 11/21/2012 02:25 AM, Jan Kara wrote:
>> On Tue 20-11-12 09:42:42, metin d wrote:
>>> I have two PostgreSQL databases named data-1 and data-2 that sit on the
>>> same machine. Both databases keep 40 GB of data, and the total memory
>>> available on the machine is 68GB.
>>>
>>> I started data-1 and data-2, and ran several queries to go over all their
>>> data. Then, I shut down data-1 and kept issuing queries against data-2.
>>> For some reason, the OS still holds on to large parts of data-1's pages
>>> in its page cache, and reserves about 35 GB of RAM to data-2's files. As
>>> a result, my queries on data-2 keep hitting disk.
>>>
>>> I'm checking page cache usage with fincore. When I run a table scan query
>>> against data-2, I see that data-2's pages get evicted and put back into
>>> the cache in a round-robin manner. Nothing happens to data-1's pages,
>>> although they haven't been touched for days.
>> Hi metin d,
>> fincore is a tool or ...? How could I get it?
>> Regards,
>> Jaegeuk
>
> Hi Jaegeuk,
>
> Yes, it is a tool, you get it from here :
> http://code.google.com/p/linux-ftools/

> Hi Metin,

> Could you give me a link to download it? I can't get it from the link
> you give me. Thanks in advance. :-)

> Regards,
> Jaegeuk

Hi Jaegeuk,

You may need to install mercurial on your system, I'm able to download source code with this command:

hg clone https://code.google.com/p/linux-ftools/

Regards,
Metin

>
>
> Regards,
> Metin
>>> Does anybody know why data-1's pages aren't evicted from the page cache?
>>> I'm open to all kind of suggestions you think it might relate to problem.
>>      Curious. Added linux-mm list to CC to catch more attention. If you run
>> echo 1 >/proc/sys/vm/drop_caches
>>      does it evict data-1 pages from memory?
>>
>>> This is an EC2 m2.4xlarge instance on Amazon with 68 GB of RAM and no
>>> swap space. The kernel version is:
>>>
>>> $ uname -r
>>> 3.2.28-45.62.amzn1.x86_64
>>> Edit:
>>>
>>> and it seems that I use one NUMA instance, if  you think that it can a problem.
>>>
>>> $ numactl --hardware
>>> available: 1 nodes (0)
>>> node 0 cpus: 0 1 2 3 4 5 6 7
>>> node 0 size: 70007 MB
>>> node 0 free: 360 MB
>>> node distances:
>>> node  0
>>>      0:  10
>>                                  Honza