Re: Problem in Page Cache Replacement

[Jaegeuk Hanse]

On 11/23/2012 04:08 PM, metin d wrote:
> ----- Original Message -----
>
> From: Jaegeuk Hanse <jaegeuk.hanse@xxxxxxxxx>
> To: metin d <metdos@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>; "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>; linux-mm@xxxxxxxxx
> 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

> 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

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