[Xenomai] memory size

[Xenomai] memory size

[ali hagigat]

My computer has 3G bytes RAM. I have disabled "high memory", PAE and
64-bit memory and I/O resources for the Xenomai kernel and the memory
size is nearly 900M (Why the memory size became smaller than 1G? By
disabling those options the size should be still 3G!) :

/root> cat /proc/meminfo
MemTotal:         894660 kB
MemFree:           56472 kB
Buffers:          110264 kB
Cached:           329584 kB
SwapCached:        47844 kB
Active:           327936 kB
Inactive:         417484 kB
Active(anon):     142080 kB
Inactive(anon):   166236 kB
Active(file):     185856 kB
Inactive(file):   251248 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       5144572 kB
SwapFree:        5014556 kB

I did it according to an Intel white paper for Xenomai. Why is it
necessary? The total memory is below 1G bytes now. Does it make the
scheduling latency higher in general? (Because I think bigger size of
the memory makes the latencies smaller. Is that right?)


Regards

Re: [Xenomai] memory size

[Gilles Chanteperdrix]

On 06/25/2012 04:21 PM, ali hagigat wrote:
> My computer has 3G bytes RAM. I have disabled "high memory", PAE and
> 64-bit memory and I/O resources for the Xenomai kernel and the memory
> size is nearly 900M (Why the memory size became smaller than 1G? By
> disabling those options the size should be still 3G!) :

This question is not related at all to Xenomai. You will find better
answers on other mailing lists than this one.

> 
> /root> cat /proc/meminfo
> MemTotal:         894660 kB
> MemFree:           56472 kB
> Buffers:          110264 kB
> Cached:           329584 kB
> SwapCached:        47844 kB
> Active:           327936 kB
> Inactive:         417484 kB
> Active(anon):     142080 kB
> Inactive(anon):   166236 kB
> Active(file):     185856 kB
> Inactive(file):   251248 kB
> Unevictable:           0 kB
> Mlocked:               0 kB
> SwapTotal:       5144572 kB
> SwapFree:        5014556 kB
> 
> I did it according to an Intel white paper for Xenomai. Why is it
> necessary? The total memory is below 1G bytes now. Does it make the
> scheduling latency higher in general? (Because I think bigger size of
> the memory makes the latencies smaller. Is that right?)

It is not necessary. And since we did not write the intel white paper,
we have no idea why this paper gives this advice.

> 
> 
> Regards
> 
> _______________________________________________
> Xenomai mailing list
> Xenomai@xenomai.org
> http://www.xenomai.org/mailman/listinfo/xenomai
> 


-- 
					    Gilles.

Re: [Xenomai] memory size

[Lennart Sorensen]

On Mon, Jun 25, 2012 at 06:51:53PM +0430, ali hagigat wrote:
> My computer has 3G bytes RAM. I have disabled "high memory", PAE and
> 64-bit memory and I/O resources for the Xenomai kernel and the memory
> size is nearly 900M (Why the memory size became smaller than 1G? By
> disabling those options the size should be still 3G!) :

Linux supports 900MB ram on x86, unless you have highmem support (which
supports up to 4GB), or PAE (which supports up to 64GB).

It has been that way for many many years.

-- 
Len Sorensen

Re: [Xenomai] memory size

[Gilles Chanteperdrix]

On 06/25/2012 08:23 PM, Lennart Sorensen wrote:
> On Mon, Jun 25, 2012 at 06:51:53PM +0430, ali hagigat wrote:
>> My computer has 3G bytes RAM. I have disabled "high memory", PAE and
>> 64-bit memory and I/O resources for the Xenomai kernel and the memory
>> size is nearly 900M (Why the memory size became smaller than 1G? By
>> disabling those options the size should be still 3G!) :
> 
> Linux supports 900MB ram on x86, unless you have highmem support (which
> supports up to 4GB), or PAE (which supports up to 64GB).
> 
> It has been that way for many many years.
> 

Not exactly, you can increase the kernel-space memory, by decreasing the
user-space applications address space, using CONFIG_VMSPLIT_2G or even
CONFIG_VMSPLIT_1G.

But if your machine is a 64 bits machine, you should probably simply
compile a 64 bits kernel.

But anyway, people elsewhere, know better than we do. See for instance:
http://linux-mm.org/HighMemory

-- 
                                                                Gilles.