linux-kernel - Re: [PATCH] trim memory not covered by WB MTRRs

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Date:	Thu, 7 Jun 2007 04:10:38 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Jesse Barnes <jesse.barnes@...el.com>
cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] trim memory not covered by WB MTRRs



On Wed, 6 Jun 2007, Jesse Barnes wrote:

> On Wednesday, June 6, 2007 4:15 pm Justin Piszcz wrote:
>> On Wed, 6 Jun 2007, Randy Dunlap wrote:
>>> On Wed, 6 Jun 2007 18:54:37 -0400 (EDT) Justin Piszcz wrote:
>>>> Hm, not sure if it was from the patch or what but I ran this:
>>>>
>>>> 1. swapoff -a
>>>> 2. ./eatmem
>>>
>>> You usually have to access the allocated memory, like:
>>>
>>> 	*d = 1.0;
>>>
>>> for it to actually be allocated (AFAIK).
>>>
>>>>    }
>>>>
>>>>    return 0;
>>>> }
>>>>
>>>> Any idea why the OOM killer can or does not kill it?
>>>
>>> What are the values of /proc/sys/vm/overcommit* ?
>>>
>>> See Documentation/vm/overcommit-accounting .
>>
>> They should be the defaults as I do not change them:
>>
>> p34:~# find /proc/|grep -i overcommit
>> /proc/sys/vm/overcommit_memory
>> /proc/sys/vm/overcommit_ratio
>> find: /proc/5128: No such file or directory
>> p34:~# cat /proc/sys/vm/overcommit_memory
>> 0
>> p34:~# cat /proc/sys/vm/overcommit_ratio
>> 50
>> p34:~#
>>
>>
>> Comments?
>
> You can be sure your memory is available if reported in /proc/meminfo or
> at boot, since those represent the actual kernel data structures used
> for memory allocation:
>
> [    0.000000] On node 0 totalpages: 2061783
>
> That corresponds to 2061783*4k = 8445063168 bytes or ~8053M.  Is that
> fairly close to what's actually installed in the machine?
>
> Note that your boot also mentions this:
>
> [  106.449661] mtrr: no more MTRRs available
>
> which indicates that things like X may not be able to map the
> framebuffer with the 'write-combine' attribute, which will hurt
> performance.  I've heard reports that turning of 'Intel QST fan
> control' in your BIOS settings will prevent all your MTRRs from being
> used (improperly, probably another BIOS bug) so that X will perform
> well.  But if you don't use X on this machine, you don't have to worry
> about it.  The other option would be to remap your MTRRs by hand to
> free one up for X, you can do that by combining the last one or two
> entries into a single MTRR using the API described in
> Documentation/mtrr.txt before you start X.
>
> Jesse
>

FYI--

[  106.449661] mtrr: no more MTRRs available

This has always occurred, even with mem=8832M setting.

Justin.
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