Re: Problem in Page Cache Replacement
From: Jaegeuk Hanse
Date: Thu Nov 22 2012 - 20:58:41 EST
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
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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/