linux-kernel - Re: Problem in Page Cache Replacement

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Date:	Fri, 23 Nov 2012 10:10:26 +0800
From:	Jaegeuk Hanse <jaegeuk.hanse@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
CC:	Metin Döşlü <metindoslu@...il.com>,
	Jan Kara <jack@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Problem in Page Cache Replacement

On 11/22/2012 11:53 PM, Fengguang Wu wrote:
> On Thu, Nov 22, 2012 at 11:41:07PM +0800, Fengguang Wu wrote:
>> On Wed, Nov 21, 2012 at 12:07:22PM +0200, Metin Döşlü wrote:
>>> On Wed, Nov 21, 2012 at 12:00 PM, Jaegeuk Hanse <jaegeuk.hanse@...il.com> wrote:
>>>> On 11/21/2012 05:58 PM, metin d wrote:
>>>>
>>>> Hi Fengguang,
>>>>
>>>> I run tests and attached the results. The line below I guess shows the data-1 page caches.
>>>>
>>>> 0x000000080000006c       6584051    25718  __RU_lA___________________P________    referenced,uptodate,lru,active,private
>>>>
>>>>
>>>> I thinks this is just one state of page cache pages.
>>> But why these page caches are in this state as opposed to other page
>>> caches. From the results I conclude that:
>>>
>>> data-1 pages are in state : referenced,uptodate,lru,active,private
>> I wonder if it's this code that stops data-1 pages from being
>> reclaimed:
>>
>> shrink_page_list():
>>
>>                  if (page_has_private(page)) {
>>                          if (!try_to_release_page(page, sc->gfp_mask))
>>                                  goto activate_locked;
>>
>> What's the filesystem used?
> Ah it's more likely caused by this logic:
>
>          if (is_active_lru(lru)) {
>                  if (inactive_list_is_low(mz, file))
>                          shrink_active_list(nr_to_scan, mz, sc, priority, file);
>
> The active file list won't be scanned at all if it's smaller than the
> active list. In this case, it's inactive=33586MB > active=25719MB. So
> the data-1 pages in the active list will never be scanned and reclaimed.

Hi Fengguang,

It seems that most of data-1 file pages are in active lru cache and most 
of data-2 file pages are in inactive lru cache. As Johannes mentioned, 
if inter-reference distance is bigger than half of memory, the pages 
will not be actived. How you intend to resolve this issue? Is Johannes's 
inactive list threshing idea  available?

Regards,
Jaegeuk

>
>>> data-2 pages are in state : referenced,uptodate,lru,mappedtodisk
>> Thanks,
>> Fengguang

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