Memory allocation from ZONE_HIGHMEM ???

Memory allocation from ZONE_HIGHMEM ???

[Pintu Agarwal]

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Hi,
 
I have a question regarding kernel memory allocation(using kmalloc) from ZONE_HIGHMEM zone.
 
I have a custom linux kernel2.6.36 running on linux mobile (arm cortexA9)
I have two zones on my system as shown by buddyinfo.
=====================================================
/opt/home/root # cat /proc/buddyinfo
Node 0, zone   Normal      2     32     22     14     12      4     12      3      0      1     23
Node 0, zone  HighMem    529    243    114     43     25     23     19     19     16     14     27
=====================================================
 
When I do memory allocation using kmalloc, the pages are allocated from Normal zone.
My allocation size is for order-10 pages = 23 * 1024 * PAGE_SIZE = 80MB
If I use more than that my allocation will fail which is obvious.
 
But I want to specifically allocate pages from ZONE_HIGHMEM instead of Normal zone.
How to explicitly do that in kernel?
 
If somebody have tried this please let me know.
 
 
 
Thanks, Regards,
Pintu

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Re: Memory allocation from ZONE_HIGHMEM ???

[Christoph Lameter]

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On Wed, 13 Jul 2011, Pintu Agarwal wrote:

> I have a question regarding kernel memory allocation(using kmalloc) from ZONE_HIGHMEM zone.

kmalloc does not allocate from ZONE_HIGHMEM.

> But I want to specifically allocate pages from ZONE_HIGHMEM instead of Normal zone.
> How to explicitly do that in kernel?

You must use the page allocator. The slab allocators cannot use
ZONE_HIGHMEM. ZONE_HIGHMEM contains pages that are not directly accessible
from the processor.