...

Hi all, The following link gives the memory map for the arm architecture. http://www.arm.linux.org.uk/developer/memory.txt

I have the following doubts.. 1) Any chipset(based on arm) manufacturer(qualcom,samsung..) should follow the same memory map. Is it hardly constrained or can be changed? Where are this constraints are implemented in the kernel source tree?

you mean, device memory map? well AFAIK that is dictated by BIOS....kernel simply just follow along...

Not the device memory map..others also like vmalloc()/ioremap region, dma_alloc() (refer that link) these regions. i refered to qualcomm chipset memory map(based on ARM9). They just mentioned only where different devices were mapped. They doesnt have this specifc adress space constraints for vmalloc, ioremap,dma_alloc etc., So i thought it is taken care by kernel. Please tell me where these constraints will be implemented? Another clarification, while assigning memory through vmalloc(), dma_alloc() kernel first should check the available address space 'taking the constraints into consideration' before returning the addresses, right? On Tue, May 31, 2011 at 12:32 PM, Mulyadi Santosa <mulyadi.santosa@gmail.com

wrote:

Hi...

I am not ARM guy, but I'll see what I can share here..... hold your breath :)

On Tue, May 31, 2011 at 12:54, sandeep kumar <coolsandyforyou@gmail.com> wrote:

...

Hi all, The following link gives the memory map for the arm architecture. http://www.arm.linux.org.uk/developer/memory.txt

I have the following doubts.. 1) Any chipset(based on arm) manufacturer(qualcom,samsung..) should follow the same memory map. Is it hardly constrained or can be changed? Where are this constraints are implemented in the kernel source tree?

you mean, device memory map? well AFAIK that is dictated by BIOS....kernel simply just follow along...

...

2) while i was student, i read in OS concepts that, "Virtual memory

gives an

...

illusion to a process, that it has always a larger continuous address space (even more than RAM) available to it."

that's true... but you need to count another limitation: addressable or not by the MMU or at least processor itself?

let's say you have 16 GiB of virtual memory, composed of 4 GiB of RAM + 12 GiB swap. Theoritically, a single process should be able to use them all, but assuming we have no PAE enabled, an 32 bit system could only address up to 4 GiB

...

So i thought i could allocate howmuch ever memory i want.

Also think about fragmentation...

...

But seeing the above link,i observed there is some limitation in the address space created by the vmalloc(). So i m now thinking that vmalloc has some limit.

Yup.....

maybe my old article could shed a light further for you: http://linuxdevcenter.com/pub/a/linux/2006/11/30/linux-out-of-memory.html

-- regards,

Mulyadi Santosa Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

-- With regards, Sandeep Kumar Anantapalli, Senior Software Engineer, Samsung India Software Operations, Bangalore.

Hi Dave,

Also keep in mind that when you vmalloc stuff you're allocating in units of pages, and there is a guard page between each allocation. So if you had 512 Mb of virtual space (which is 131,072 pages), you'll be able to vmalloc a maximum of 65536 objects or 1 page each. Fewer objects if they're bigger than a page.

A quick question, Suppose if I alloc 1MB of memory using vmalloc,Is there a guard page between each page or is it after the 1MB. With Regards, Subin K G On Tue, May 31, 2011 at 10:19 AM, Dave Hylands <dhylands@gmail.com> wrote:

Hi Sandeep,

On Mon, May 30, 2011 at 10:54 PM, sandeep kumar <coolsandyforyou@gmail.com> wrote:

...

Hi all, The following link gives the memory map for the arm architecture. http://www.arm.linux.org.uk/developer/memory.txt

I have the following doubts.. 1) Any chipset(based on arm) manufacturer(qualcom,samsung..) should follow the same memory map. Is it hardly constrained or can be changed? Where are this constraints are implemented in the kernel source tree?

You can have 2 different configurations for the same chip which present totally different memory maps. Where things are physically in memory varies from chip to chip, regardless of the fact that they happen to use the same processor.

...

2) while i was student, i read in OS concepts that, "Virtual memory gives an illusion to a process, that it has always a larger continuous address space (even more than RAM) available to it." So i thought i could allocate howmuch ever memory i want. But seeing the above link,i observed there is some limitation in the address space created by the vmalloc(). So i m now thinking that vmalloc has some limit.

Absolutely. You can only vmalloc as much memory as there is virtual space reserved for vmalloc. And your vmalloc memory space can become fragmented, so you could have lots of space, but not have enough contiguous virtual space left to allocate a large object.

Also keep in mind that when you vmalloc stuff you're allocating in units of pages, and there is a guard page between each allocation. So if you had 512 Mb of virtual space (which is 131,072 pages), you'll be able to vmalloc a maximum of 65536 objects or 1 page each. Fewer objects if they're bigger than a page.

The actual allocation of vmalloc memory is determined by the macros VMALLOC_START and VMALLOC_END. VMALLOC_START is defined in arch/arm/include/asm/pgtable.h: http://lxr.linux.no/linux+v2.6.39/arch/arm/include/asm/pgtable.h#L41 although it can be overriden by a particular architecture.

VMALLOC_END is normally defined in the machine's memory.h file, and it sits somewhere between VMALLOC_START and the beginning of I/O space.

-- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com

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-- With Regards Subin Gangadharan Everything should be made as simple as possible,but not simpler.