On 13:45 Sat 24 Nov , Peter Teoh wrote: > I have been looking for answer for this but never seem to get anywhere. > > Supposed I have 16GB of physical memory, my question is, in 32bit x86 > linux, how can I use the physical memory beyond the 4GB boundary in my > kernel drivers? > > 1. What CONFIG parameters for kernel compilation is needed (or is > for this purpose)? There is a "HIGHMEM" config option which can be set to off, 4GB and 64GB. > 2. Which are the main key functions or global variable for going > this? The pagetable is still the same mem_map right? I am afraid, that I have not understood your question very well. When turning on highmem, the address space layout changes. There is a 3GB/1GB split of the address space on i386. This means that the lower 3GB are used by user space programs to address virtual memory. The upper 1GB can only be accessed in kernel mode and is directly mapped to the physical memory. You can also choose a 2GB/2GB or 1GB/3GB layout. It you enable highmem, a part of the kernel address space is not directly mapped to physical memory. Instead it is used to map the high memory before accessing it. After the access, it is unmapped. This allows addressing more memory at the cost of higher cpu load. However, the code that allocates/accesses the memory has to deal with highmem. Michi -- programing a layer 3+4 network protocol see http://michaelblizek.homelinux.net -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
