2009-10-08 18:29:30

by Andreas

Subject: Allocated Mem - 700MB missing

Hi experts!

Where are the missing 700MB ??? (4GB installed)
700 MB is too much, that can't be only because of version-differences!

I compared (unmodified) stable/testing kernels with Xen and OpenVZ-kernel:
all out of main debian packages:

Only3200:
----------
*Linux host 2.6.18-5-686 #1 SMP Mon Dec 24 16:41:07 UTC 2007 i686 GNU/Linux
*Linux knoppix 2.6.24.4 #2 SMP PREEMPT Tue Mar 25 21:35:28 CET 2008 i686 GNU/Linux
*Linux host 2.6.26-2-686 #1 SMP Sun Jun 21 04:57:38 UTC 2009 i686 GNU/Linux


Full4GB:
---------
*Linux host 2.6.26-2-openvz-686 #1 SMP Sun Jun 21 07:07:25 UTC 2009 i686 GNU/Linux

I'm using:
Dell Optiplex 755
Board Product name (DMI): 0GM819
2x2GB (4064MB) installed


Here the output of free:

#mem: Only3200free:
total used free shared buffers cached
Mem: 3358232 30760 3327472 0 1668 13608
-/+ buffers/cache: 15484 3342748
Swap: 0 0 0

#memOnly3200freeXenDom0.txt:
total used free shared buffers cached
Mem: 3873216 136068 3737148 0 1024 12852
-/+ buffers/cache: 122192 3751024
Swap: 0 0 0

#memOnly3900free-2.6.30.1-amd64.txt:
total used free shared buffers cached
Mem: 3920696 606612 3314084 0 14608 251372
-/+ buffers/cache: 340632 3580064
Swap: 7831676 0 7831676

#memFull4GBfree-OpenVZ (Dom0):
total used free shared buffers cached
Mem: 4003584 451420 3552164 0 8132 143652
-/+ buffers/cache: 299636 3703948
Swap: 0 0 0

I attached the output of dmesg and proc/meminfo of
the normal kernel (only 3200M) and openVZ-kernel (gives full 4GBs)
XenDom0 gives 3900, which is ok.

i*)Question2:
Do I have better performance, if installed to DIMM1+3 (next to each other)
=> Bios says: asynchronous,
or DIMM1+2 (3 inbetween them left out) => Bios says: synchronous ?


Please be so kind and also send your answer to andreas2 (AT)
logic.univie.ac.at (I didn't subscribe to the group)


thanks!
Andrew

2009-10-08 18:38:27

by Maciej Rutecki

Subject: Re: Allocated Mem - 700MB missing

Look at Your config option:
CONFIG_HIGHMEM4G
CONFIG_NOHIGHMEM

Regards
--
Maciej Rutecki
http://www.maciek.unixy.pl

2009-10-09 01:15:52

by Robert Hancock

Subject: Re: Allocated Mem - 700MB missing

On 10/08/2009 11:59 AM, Andreas wrote:
> Hi experts!
>
> Where are the missing 700MB ??? (4GB installed)
> 700 MB is too much, that can't be only because of version-differences!
>
> I compared (unmodified) stable/testing kernels with Xen and OpenVZ-kernel:
> all out of main debian packages:
>
> Only3200:
> ----------
> *Linux host 2.6.18-5-686 #1 SMP Mon Dec 24 16:41:07 UTC 2007 i686 GNU/Linux
> *Linux knoppix 2.6.24.4 #2 SMP PREEMPT Tue Mar 25 21:35:28 CET 2008 i686 GNU/Linux
> *Linux host 2.6.26-2-686 #1 SMP Sun Jun 21 04:57:38 UTC 2009 i686 GNU/Linux
>
>
> Full4GB:
> ---------
> *Linux host 2.6.26-2-openvz-686 #1 SMP Sun Jun 21 07:07:25 UTC 2009 i686 GNU/Linux

Check the kernel configuration. For 32-bit kernels you need
CONFIG_HIGHMEM64G enabled to use memory above 4GB (including in your
case, because of the PCI, etc. memory holes). Though it would be better
to use a 64-bit kernel.