[CLOSED] Memory allocation with pages.

[Brendan]

Hi,

In my kernel the first physical 4 MB are mapped to the first virtual 4 MB. The first 640 KB are in the stack of free physical pages yet (until I will more understand). All the 4 MB are marked as free in the page table.

In that case; there's nothing wrong with having pages mapped into the "mapping of the first 4 MiB of the physical address space" and also mapped elsewhere or used as page tables, etc.

Also note that this is a relatively common trick used by a lot of people as a temporary thing during boot (e.g. before the kernel has setup the virtual address space properly and mapped/shifted itself to 0xFFFFFFFF80000000); where that temporary "mapping of the first 4 MiB of the physical address space" is removed after.

And I want free physical pages to be more than 160 (160 * 4096 = 655360 = 640 KB). How can I do that (how to split the memory)?

Normally boot code gets a "memory map" from the firmware and passes it to your kernel; and when initialising the physical memory manager you parse this "memory map" and find any/all "usable RAM" areas from it. Then (for each "usable RAM" area) you break it up into pages; and (for each page in a "usable RAM" area), make sure that you aren't actually using the page (e.g. for kernel, etc), and tell the physical memory manager the page is free/usable RAM.


Cheers,

Brendan

[ExeTwezz]

Thank you all