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

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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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