linux-kernel - Re: Why active list and inactive list?

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Message-ID: <45B57E73.3000307@in.ibm.com>
Date:	Tue, 23 Jan 2007 08:48:11 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Christoph Lameter <clameter@....com>
CC:	Andrea Arcangeli <andrea@...e.de>,
	Niki Hammler <mailinglists@...aq.net>,
	linux-kernel@...r.kernel.org,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: Why active list and inactive list?

Christoph Lameter wrote:
> On Tue, 23 Jan 2007, Balbir Singh wrote:
> 
>> This makes me wonder if it makes sense to split up the LRU into page
>> cache LRU and mapped pages LRU. I see two benefits
>>
>> 1. Currently based on swappiness, we might walk an entire list
>>    searching for page cache pages or mapped pages. With these
>>    lists separated, it should get easier and faster to implement
>>    this scheme
>> 2. There is another parallel thread on implementing page cache
>>    limits. If the lists split out, we need not scan the entire
>>    list to find page cache pages to evict them.
>>
>> Of course I might be missing something (some piece of history)
> 
> This means page cache = unmapped file backed page right? Otherwise this
> would not work. I always thought that the page cache were all file backed
> pages both mapped and unmapped.
> 

Yes, unfortunately my terminology was not clear. I mean unmapped file
backed pages.

> With the proposed schemd you would have to move pages between lists if
> they are mapped and unmapped by a process. Terminating a process could
> lead to lots of pages moving to the unnmapped list.
> 

When you unmap or map, you need to touch the pte entries and know the
pages involved, so shouldn't be equivalent to a list_del and list_add
for each page impacted by the map/unmap operation?

-- 
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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