get Page size

eshwar_ind · 02-23-2004, 11:29 PM

Hi!
How can we get the page size in linux. Can i change that in in aprogram?
In Kernel module programming is there any way to get the memory pieces just like 10 bytes, 2 bytes? ( i think kmalloc allocates entire page if the requested memory is less than the page size So its a waste of remaining memory)
Please reply me.
bye,
Eshwar.

jinksys · 02-24-2004, 04:01 AM

To get page size:

Code:

#include <stdio.h>
#include <unistd.h>

int main()
{
printf("%i,	getpagesize());
return 0;
}

Simply put, you cant change the page size. And due to the way the kernel allocates memory and fragmentation within the system's physical memory, memory allocation with kmalloc isn't precise as with malloc. You'll often get a pointer to a larger chunk of memory than requested, sometimes up to double the amount.

infamous41md · 02-24-2004, 02:45 PM

to add one thing to the above, kmalloc keeps around a pool of various sized memory objects. whether or not there is one as small as 10 bytes, i doubt, but you should recieve the next largest chunk if that pool has a free chunk. if you are going to be allocating a large quantity of constant size memory chunks, you may want to look into having kmalloc create a special pool of objects for you of that size using kmem_cache_create() and kmem_cache_alloc() from [kernel/slab/mm.c].

jinksys · 02-24-2004, 08:17 PM

I seriously doubt youll get a buffer of 10bytes using kmalloc, since the minimum memory that kmalloc handles is anywhere from 32 to 64 bytes, depending on page size and kernel.

eshwar_ind · 02-25-2004, 12:49 AM

Quote:

Originally posted by jinksys
I seriously doubt youll get a buffer of 10bytes using kmalloc, since the minimum memory that kmalloc handles is anywhere from 32 to 64 bytes, depending on page size and kernel.

eshwar_ind · 02-25-2004, 12:50 AM

Hi guys thank you very much.