increase lowmem value for ppc

Ruksen INANIR rukseninanir at
Thu Jul 17 21:51:36 EST 2008

Thanks for your comments.
I tried the highmem option but one of the device drivers does not 
support highmem, so it did not work.
the only choice for me is to increase the lowmem to 1520 MB. the maximum 
lowmem value i reached succesfully is 1503 MB. but any value more than 
1503 results kernel not able to load kernel modules.
Upgrading to a 2.6.x kernel may solve the problem, but it needs a lot of 
effort. Does 2.6.x kernel support 2G physical memory?

Marco Stornelli wrote:
> Ruksen INANIR ha scritto:
>> Is there any side effects of changing the address splitting? 
> Yes, in this way the application address space is smaller than normal. 
> Some big applications (for example same dbms) might not work. Usually 
> with 2G/2G most of the applications work well.
>> What should i change for 2G/2G splitting? should i shift the kernel 
>> start?
>> Thanks
> Yes in advanced options of the kernel menu, but sometimes it's not 
> easy.  Sometimes ago I had to do the same thing but I have to change 
> the kernel code because some operations were hard-coded. Be careful 
> because it's not an easy operation. However I'd suggest you to use the 
> highmem, the memory performance are worse than direct memory mapping, 
> but usually it's not a problem because the overhead is low.
>> Marco Stornelli wrote:
>>> Marco Stornelli ha scritto:
>>>> Ruksen INANIR ha scritto:
>>>>> Is there a way to increase the lowmem value for ppc. The 
>>>>> MAX_LOW_MEM is defined as max 768 MB. But a value around 1.5 G 
>>>>> works with no problem. But when i try to increase this value to 
>>>>> 1520 or more, kernel complaints about no space for memory 
>>>>> allocation when loading kernel modules.
>>>>> I do not want to use HIGHMEM config. What is the max lowmem value 
>>>>> for a ppc system? What other setting are needed to use 1520 MB (or 
>>>>> more) as lowmem .
>>>>> The ppc card has 2G on board memory. 2.4.22 kernel is used.
>>>>> Thanks
>>>>> _______________________________________________
>>>>> Linuxppc-embedded mailing list
>>>>> Linuxppc-embedded at
>>>> With 32-bit arch you may not use more than 1GB to map the memory 
>>>> (minus some space for some kernel operation). The value of 768MB 
>>>> was not there by chance.
>>> Only an additional comment: I meant with the address splitting 
>>> 3G/1G. To map more than 1GB, you have to change the splitting 2G/2G 
>>> for example.
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