From: Jaegeuk Hanse <jaegeuk.hanse@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>, metin d <metdos@yahoo.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org
Subject: Re: Problem in Page Cache Replacement
Date: Fri, 23 Nov 2012 10:14:07 +0800 [thread overview]
Message-ID: <50AEDBEF.8070408@gmail.com> (raw)
In-Reply-To: <20121122161743.GH24381@cmpxchg.org>
On 11/23/2012 12:17 AM, Johannes Weiner wrote:
> On Thu, Nov 22, 2012 at 09:16:27PM +0800, Jaegeuk Hanse wrote:
>> On 11/22/2012 09:09 AM, Johannes Weiner wrote:
>>> On Thu, Nov 22, 2012 at 08:48:07AM +0800, Jaegeuk Hanse wrote:
>>>> On 11/22/2012 05:34 AM, Johannes Weiner wrote:
>>>>> Hi,
>>>>>
>>>>> On Tue, Nov 20, 2012 at 07:25:00PM +0100, 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.
>>>>>>>
>>>>>>> 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.
>>>>> This might be because we do not deactive pages as long as there is
>>>>> cache on the inactive list. I'm guessing that the inter-reference
>>>>> distance of data-2 is bigger than half of memory, so it's never
>>>>> getting activated and data-1 is never challenged.
>>>> Hi Johannes,
>>>>
>>>> What's the meaning of "inter-reference distance"
>>> It's the number of memory accesses between two accesses to the same
>>> page:
>>>
>>> A B C D A B C E ...
>>> |_______|
>>> | |
>>>
>>>> and why compare it with half of memoy, what's the trick?
>>> If B gets accessed twice, it gets activated. If it gets evicted in
>>> between, the second access will be a fresh page fault and B will not
>>> be recognized as frequently used.
>>>
>>> Our cutoff for scanning the active list is cache size / 2 right now
>>> (inactive_file_is_low), leaving 50% of memory to the inactive list.
>>> If the inter-reference distance for pages on the inactive list is
>>> bigger than that, they get evicted before their second access.
>> Hi Johannes,
>>
>> Thanks for your explanation. But could you give a short description
>> of how you resolve this inactive list thrashing issues?
> I remember a time stamp of evicted file pages in the page cache radix
> tree that let me reconstruct the inter-reference distance even after a
> page has been evicted from cache when it's faulted back in. This way
> I can tell a one-time sequence from thrashing, no matter how small the
> inactive list.
>
> When thrashing is detected, I start deactivating protected pages and
> put them next to the refaulted cache on the head of the inactive list
> and let them fight it out as usual. In this reported case, the old
> data will be challenged and since it's no longer used, it will just
> drop off the inactive list eventually. If the guess is wrong and the
> deactivated memory is used more heavily than the refaulting pages,
> they will just get activated again without incurring any disruption
> like a major fault.
Hi Johannes,
If you also add the time stamp to the protected pages which you deactive
when incur thrashing?
Regards,
Jaegeuk
next prev parent reply other threads:[~2012-11-23 2:14 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=50AEDBEF.8070408@gmail.com \
--to=jaegeuk.hanse@gmail.com \
--cc=hannes@cmpxchg.org \
--cc=jack@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=metdos@yahoo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).