From: Jaegeuk Hanse <jaegeuk.hanse@gmail.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: metin d <metdos@yahoo.com>, Jan Kara <jack@suse.cz>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: Problem in Page Cache Replacement
Date: Wed, 21 Nov 2012 17:42:33 +0800 [thread overview]
Message-ID: <50ACA209.9000101@gmail.com> (raw)
In-Reply-To: <20121121090204.GA9064@localhost>
On 11/21/2012 05:02 PM, Fengguang Wu wrote:
> On Wed, Nov 21, 2012 at 04:34:40PM +0800, Jaegeuk Hanse wrote:
>> Cc Fengguang Wu.
>>
>> On 11/21/2012 04:13 PM, metin d wrote:
>>>> 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?
>>> I'm guessing it'd evict the entries, but am wondering if we could run any more diagnostics before trying this.
>>>
>>> We regularly use a setup where we have two databases; one gets used frequently and the other one about once a month. It seems like the memory manager keeps unused pages in memory at the expense of frequently used database's performance.
>>> My understanding was that under memory pressure from heavily
>>> accessed pages, unused pages would eventually get evicted. Is there
>>> anything else we can try on this host to understand why this is
>>> happening?
> We may debug it this way.
>
> 1) run 'fadvise data-2 0 0 dontneed' to drop data-2 cached pages
> (please double check via /proc/vmstat whether it does the expected work)
>
> 2) run 'page-types -r' with root, to view the page status for the
> remaining pages of data-1
>
> The fadvise tool comes from Andrew Morton's ext3-tools. (source code attached)
> Please compile them with options "-Dlinux -I. -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE"
>
> page-types can be found in the kernel source tree tools/vm/page-types.c
>
> Sorry that sounds a bit twisted.. I do have a patch to directly dump
> page cache status of a user specified file, however it's not
> upstreamed yet.
Hi Fengguang,
Thanks for you detail steps, I think metin can have a try.
flags page-count MB symbolic-flags long-symbolic-flags
0x0000000000000000 607699 2373
___________________________________
0x0000000100000000 343227 1340
_______________________r___________ reserved
But I have some questions of the print of page-type:
Is 2373MB here mean total memory in used include page cache? I don't
think so.
Which kind of pages will be marked reserved?
Which line of long-symbolic-flags is for page cache?
Regards,
Jaegeuk
>
> Thanks,
> Fengguang
>
>>> 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.
>>>>
>>>> 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
next prev parent reply other threads:[~2012-11-21 9:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-20 17:42 Problem in Page Cache Replacement metin d
2012-11-20 18:25 ` Jan Kara
2012-11-21 8:03 ` metin d
2012-11-21 8:13 ` metin d
2012-11-21 8:34 ` Jaegeuk Hanse
2012-11-21 9:02 ` Fengguang Wu
2012-11-21 9:10 ` Fengguang Wu
2012-11-21 9:42 ` Jaegeuk Hanse [this message]
2012-11-21 10:00 ` metin d
[not found] ` <1353491880.11679.YahooMailNeo@web141102.mail.bf1.yahoo.com>
[not found] ` <50ACA634.5000007@gmail.com>
2012-11-21 10:07 ` Metin Döşlü
2012-11-22 15:41 ` Fengguang Wu
2012-11-22 15:53 ` Fengguang Wu
2012-11-23 2:10 ` Jaegeuk Hanse
2012-11-25 20:08 ` Rik van Riel
2012-11-24 15:06 ` Metin Döşlü
2012-11-22 15:26 ` Fengguang Wu
2012-11-23 1:32 ` Jaegeuk Hanse
2012-11-23 2:25 ` Fengguang Wu
2012-11-21 21:34 ` Johannes Weiner
2012-11-21 22:01 ` metin d
2012-11-22 0:48 ` Jaegeuk Hanse
2012-11-22 1:09 ` Johannes Weiner
2012-11-22 9:37 ` metin d
2012-11-22 13:16 ` Jaegeuk Hanse
2012-11-22 16:17 ` Johannes Weiner
2012-11-23 2:14 ` Jaegeuk Hanse
2012-11-23 1:58 ` Jaegeuk Hanse
2012-11-23 8:08 ` metin d
2012-11-23 8:17 ` Jaegeuk Hanse
2012-11-23 8:25 ` metin d
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