increase lowmem value for ppc

increase lowmem value for ppc

[Ruksen INANIR]

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

Re: increase lowmem value for ppc

[Marco Stornelli]

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@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
> 
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.

-- 
Marco Stornelli
Embedded Software Engineer
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
http://www.coritel.it

marco.stornelli@coritel.it
+39 06 72582838

Re: increase lowmem value for ppc

[Marco Stornelli]

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@ozlabs.org
>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>
> 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.

-- 
Marco Stornelli
Embedded Software Engineer
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
http://www.coritel.it

marco.stornelli@coritel.it
+39 06 72582838

Re: increase lowmem value for ppc

[Ruksen INANIR]

Is there any side effects of changing the address splitting? What should 
i change for 2G/2G splitting? should i shift the kernel start?
Thanks


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@ozlabs.org
>>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>>
>> 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.
>

Re: increase lowmem value for ppc

[Marco Stornelli]

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@ozlabs.org
>>>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>>>
>>> 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.
>>
> 
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
> 


-- 
Marco Stornelli
Embedded Software Engineer
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
http://www.coritel.it

marco.stornelli@coritel.it
+39 06 72582838

Re: increase lowmem value for ppc

[Ruksen INANIR]

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@ozlabs.org
>>>>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>>>>
>>>> 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.
>>>
>>
>> _______________________________________________
>> Linuxppc-embedded mailing list
>> Linuxppc-embedded@ozlabs.org
>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>
>
>

Re: increase lowmem value for ppc

[Marco Stornelli]

Ruksen INANIR ha scritto:
> 
> Thanks for your comments.
> I tried the highmem option but one of the device drivers does not 
> support highmem, so it did not work.

Strange....you can try to look at it, it could be only some GFP flag.

> 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.

Mmmm....have you tried a stress test? It sounds like a bit strange that 
the kernel works well with this mapping but without other modification.

> 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?
> 
It's the same. Some architecture have 36-bit addressing, but I don't 
know if the latest kernel has the support for this feature for powerpc.
> 
> 
> 
> 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@ozlabs.org
>>>>>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>>>>>
>>>>> 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.
>>>>
>>>
>>> _______________________________________________
>>> Linuxppc-embedded mailing list
>>> Linuxppc-embedded@ozlabs.org
>>> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>>>
>>
>>
> 
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
> 


-- 
Marco Stornelli
Embedded Software Engineer
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
http://www.coritel.it

marco.stornelli@coritel.it
+39 06 72582838

Re: increase lowmem value for ppc

[Siva Prasad]

Marco Stornelli wrote:

> Upgrading to a 2.6.x kernel may solve the problem, but it needs a lot
of=20
> effort. Does 2.6.x kernel support 2G physical memory?
>=20
It's the same. Some architecture have 36-bit addressing, but I don't=20
know if the latest kernel has the support for this feature for powerpc.
>=20

I think recently there were some patches with 2.6.26-rcx to support
36-bit addressing and changed the addressing to phys_addr_t type from
unsigned long, and few other changed. I think this should be available
starting 2.6.26 version.