pmm

Stanix’s pmm (physical memory manager) is the lowest level allocator. Pmm functions and data structures are defined in <kernel/pmm.h>. It allocate and manage the life time of pages, a page being a 4KB block (see PAGE_SIZE). New pages can be allocated with pmm_allocate_page and freed with pmm_free_page. Newly allocated pages start with a ref count of 1, that can incremented using pmm_retain and decreased using pmm_free_page. A page’s data can be duplicated using pmm_dup_page. Each physical page (outside MMIO/ACPI regions) have an associed page_t that track the ref count and status of a page (is it dirty, in use, …). A page_t can be accessed from a physical page adress using pmm_page_info. Modifications of the page_t should always be done using atomics. The zero page is a special page always guaranted to be full of zeros. A new ref to the zero page can be optained using pmm_get_zero_page. The zero page should never be written.