On 12/11/06, Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx> wrote:
Hi Bahadir....sorry for this late reply...
No problem.. ;-)
Let me put this thing clearer, you mean what will happen if kernel space mapping changes? I haven't done close observation about it, but from what I read in UTLK, the kernel does "deferred" update of master kernel Page Global Directory. Mulyadi
Yes I mean't the kernel mappings. This is probably quite arch-specific, but AFAIK a PGD is maintained for each process, and since the kernel area is fixed, (assuming 1G/3G mapping) it only requires changing the (cr0 on x86?) pgd pointer register and a tlb/cache flush upon a context switch. I was expecting that the kernel memory allocators, (buddy/slab and anything else allocation related) would change the kernel mappings frequently if not always, when some memory is allocated to user or kernel space. The question is, is it really frequent, if at all? If the whole of physical memory (up to 4GB in a 32-bit system) is virtually mapped to the kernel at initialisation, then any time userland wants memory, tables need modification. Else if it is partially mapped, as kernel runs out of mapped memory, tables (most possibly pgds, since they map for bigger chunks) would need modification. Does anyone know how this is done precisely, say, on x86? Back to your comment, lazy modification makes sense, since pgds won't need updating unless the process it belongs to is scheduled to run. It's been one of my longer emails for a while ;-) Thanks, Bahadir -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
