On 18-11-07 20:08, Talib Alim wrote:
I am writing sendpage (this is called when sendfile system call is
used) function for my protocol. User application calls with socket and
filename, kernel maps file and pass struct page * to sendpage function.
I use following expression to get virtual address and copy data
virtual_address = phys_to_virt(page_to_pfn(page) << PAGE_SHIFT);
This works fine on Pentium III machine with 515324 KB memory, but when
I run same code on Xeon with 2074604 KB memory, I get
Unable to handle kernel paging request at virtual address 3ab6c000
Is this because this address (struct page *) is not mapped ? how do I
check in my code whether it is mapped or not, since it is mapped on
Pentium.
Your virtual_address= only works for lowmem, the permanently and 1:1 mapped
portion of physical memory. With the standard 3:1 user/kernel split, there's
room for at most 896M of that. Your P3 will therefore have all its 512M as
lowmem, but the 2G Xeon will (probably I should say, check your dmesg) be
using most of it as highmem.
You should look into kmap{,_atomic}() to map highmem.
Rene.
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