So, in the start, the page might have kernel mode address, but in the end it has user mode address. But kernel is still the one that tracks all the page...be it anonymous or non anonymous ones.
Not really. In this particular case of .nopage (page fault handler) of vma, we already have a user space virtual address for the faulty page, we just need it to map it with a physical page frame (RAM or device memory). Just allocate a physical page frame without any address, caller for .nopage will take care of properly setting its user space virtual address (page->va). So, no association with kernel space virtual address is required, e.g. it can be high memory page too without any kernel mapping. Rajat On Sat, Feb 19, 2011 at 2:10 PM, Mulyadi Santosa <mulyadi.santosa@gmail.com> wrote:
Hi :)
I'll try to help...
On Sat, Feb 19, 2011 at 13:10, anish singh <anish198519851985@gmail.com> wrote:
As i understood whenver a user space program is run it is represented in kernel using VMA which is managed by struct mm_struct and whenever the program is trying to read/write to a memory location in user space it will be directed to physical address using PAGE TABLE translation done by struct mm_struct(done in kernel space).Am i right?
i think not "done" but mm_struct points to PGD that represent's the whole process address space. Using information provided there, MMU does translation.
Suppose a simple driver wants the user to directly access its device memory then we use mmap.This mmap associates a set of user space virtual address with device driver memory and it is done by creating kernel page tables for the user space virtual addresses.Is the page table translation done everytime whenever user space does read/write to the device memory??
if it's recently translated, quite likely it is already cached in TLB (translation look aside buffer)
In .nopage function call we return the page associated with the physical address which the user wants to associate with user space virtual address.Is the page address returned by the nopage function same as seen by the user or will it be converted to user space virtual address(range between 0-2 GB)?
AFAIK, nopage is one of the functions that handle minor page fault, no?
Anyway, memory allocation, usually start by kernel allocates a page. Then it is "handed" to user space memory allocator.
So, in the start, the page might have kernel mode address, but in the end it has user mode address. But kernel is still the one that tracks all the page...be it anonymous or non anonymous ones.
Does it help? :)
-- regards,
Mulyadi Santosa Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
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