Message-ID: <45B5A26A.3060209@in.ibm.com>
Date: Tue, 23 Jan 2007 11:21:38 +0530
From: Balbir Singh <balbir@in.ibm.com>
Reply-To: balbir@in.ibm.com
Organization: IBM
User-Agent: Thunderbird 1.5.0.9 (X11/20070103)
MIME-Version: 1.0
To: Rik van Riel <riel@redhat.com>
CC: Nick Piggin <nickpiggin@yahoo.com.au>, Andrea Arcangeli <andrea@suse.de>,
       Niki Hammler <mailinglists@nobaq.net>, linux-kernel@vger.kernel.org,
       Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Subject: Re: Why active list and inactive list?
References: <45B55286.5060909@nobaq.net> <20070123003939.GY13798@opteron.random> <45B56575.10807@in.ibm.com> <45B58C5C.8010900@yahoo.com.au> <45B59053.1060007@redhat.com>
In-Reply-To: <45B59053.1060007@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2269
Lines: 67

Rik van Riel wrote:
> Nick Piggin wrote:
> 
>> The other nice thing about it was that it didn't have a hard
>> cutoff that the current reclaim_mapped toggle does -- you could
>> opt to scan the mapped list at a lower ratio than the unmapped
>> one. Of course, it also has some downsides too, and would
>> require retuning...
> 
> Here's a simple idea for tuning.
> 
> For each list we keep track of:
> 1) the size of the list
> 2) the rate at which we scan the list
> 3) the fraction of (non new) pages that get
>    referenced
> 
> That way we can determine which list has the largest
> fraction of "idle" pages sitting around and consequently
> which list should be scanned more aggressively.
> 
> For each list we can calculate how frequently the pages
> in the list are being used:
> 
> pressure = referenced percentage * scan rate / list size
> 
> The VM can equalize the pressure by scanning the list with
> lower usage less than the other list.  This way the VM can
> give the right amount of memory to each type.
> 

This sounds like a good thing to start with. I think we can
then use swappiness to decide what to evict.

> Of course, each list needs to be divided into inactive and
> active like the current VM, in order to make sure that the
> pages which are used once cannot push the real working set
> of that list out of memory.
> 

Yes, that makes sense.

> There is a more subtle problem when the list's working set
> is larger than the amount of memory the list has.  In that
> situation the VM will be faulting pages back in just after
> they got evicted.  Something like my /proc/refaults code
> can detect that and adjust the size of the undersized list
> accordingly.
> 
> Of course, once we properly distinguish between the more
> frequently and less frequently accessed pages within each
> of the page sets (mapped/anonymous vs. unmapped) and have
> the pressure between the lists equalized, why do we need
> to keep them separate again?
> 

:-)

-- 
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/