how to reserve memory in linux?

[Rahul]

On 10/21/06, Ming Liu <eemingliu at hotmail.com> wrote:
>
> Dear sudheer,
> About the "mem=xx" argument, I checked it from the website and got such a
> explanation:
>
> This argument has several purposes: The original purpose was to specify
> the
> amount of installed memory (or a value less than that if you wanted to
> limit the amount of memory available to linux).
>
> From the argument above, it says "mem=xx" is to specify the amount of
> memory available to Linux. I am not sure if I am right, but I think if I
> use such an argument, that reserved part (that 5MB you mentioned), is not
> available any more for Linux to access it.
>
> My original meaning is: specify a fixed physical address for a mount of
> memory for reserved use. The point is to make this part of memory fixed in
> the memory of physical address, and then another I/O peripheral could use
> DMA to access such a fixed physical address memory. However if I don't
> reserve such a part, I must let Linux to allocate such a memory part. And
> then Linux will not put it in a fixed physical address


yes

and then the
> peripheral will not know where is this part.


why do you think so ?
Can't you give the physical address of the allocated memory from linux
kernel to peripheral's DMA.?
Unless you need to hardcode the physicall address i hope
virt_to_phys(kmalloc_address) can be given to DMA.
Sorry if i am still wrong in understanding your requirement.


Am I right? Thanks for your idea.
>
> Also other ideas are appreciated.
>
> Regards
> Ming
>
> >Considering your setup as normal desktop, I hope this can be done by
> >giving
> >"mem= xxm"  as the boot arguments.  Say the dmesg in your system
> >shows   "
> >495MB LOWMEM available."  .  In the boot arguments you can give
> >mem=490m
> >saying the linux to use only 490MB . The rest 5MB can be used later
> >as you
> >wish.
>
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