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My main problem now is where to store everything in the memory

I'm gonna use a self-mapping page directory (haven't done that before but it seems to have great benefits).

and a long array that represents free/used pages. I cannot really have this "free pages mask" among the kernel code, since it must exist before I load the kernel. Is this a good way of doing this?

mangaluve wrote:Just a short follow up, what about the 1 MB limit, you said I should put my kernel above the first 1 MB of memory. Why is that?

mangaluve wrote:Thanks a lot! I guess I could just identity-map the first MB and not touch it after that..?

mangaluve wrote:The main thing Im wondering is where to store page-information, such as free pages. I thought about having a big array, with one bit for each page, saying whether its free or not, at a pre-determined location. Is this good enough? As I said, I want to minimize the number of "hardcoded" physical addresses, I'd prefer to fetch all memory from a page allocator as soon as possible.

mangaluve wrote:Maybe I could use some space just above the 1 MB mark (physical) to store the page directory and the free-pages-array, and map it to the top of my virtual memory? Of course, it would be nice to have this free-pages-array on a dynamic kernel heap, but maybe that's not good (since I need a page allocator for my heap)? Im just interested in different ways, pros/cons and so on...

mangaluve wrote:I was thinking of though..suppose the first 4 bytes in every free page points to the next free, as a linked list (I'll probably use a buddy system). Now suppose I want to manipulate this, allocating pages and change those pointers. Well, the problem is that I have paging enabled, so I havent mapped any virtual address to those physical pages.

mangaluve wrote:Isnt it correct that when I enable/disable paging, I _MUST_ do it from identity-mapped code?

mangaluve wrote:I'd like to load the physical page allocator before the kernel. Fine, I load it somewhere. But then (in another stage, or in the kernel), I want to enable paging. But I still need to reach the page-allocator code somehow. So I have to map the page-allocator to virtual memory. But since the page-allocator must be able to run without paging (when I boot), it has to be identity mapped? Idealy, the page allocator shouldnt know anything at all about paging.

osdnlo wrote:Wouldn't a linked list just make performance lower?

// Page must remain mapped into the virtual address space until after it's freed

void free_phys_page(void *virtual_address, void *physical_address) {
    // Acquire re-entrancy lock if necessary
    *(void **)virtual_address = top_free_page;
    top_free_page = physical_address;
    // Release re-entrancy lock if necessary
}


// Page must be mapped into the virtual address space, then allocated

void *start_alloc_phys_page(void) {
    // Acquire re-entrancy lock if necessary
    return top_free_page;
}

void *complete_alloc_phys_page(void *virtual_address, void *physical_address) {
    top_free_page = *(void **)virtual_address;
    // Release re-entrancy lock if necessary
}