Page Frame Reclaim

在 user task exit 時，需要將在 user space 使用的 page 以及對應的 page entry 做回收，這件事是由即將 exit 的 user task 自己處理。kernel space 所用到的 page (e.g. kernel stack) 會由 task reaper 回收。

src/schedule.c

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void do_exit(int status) {
    current_task->state = ZOMBIE;
    current_task->exit_status = status;

    // reclaim all allocated pages
    page_reclaim(current_task->mm.pgd);

    schedule();
}

src/mm.c

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void page_free(void* page_virt_addr) {
    uint64_t pfn = phy_to_pfn(virtual_to_physical((uint64_t)page_virt_addr));
    page[pfn].used = AVAL;
    remain_page++;
}

void page_reclaim_pte(uint64_t pte_phy) {
    uint64_t* pte = (uint64_t*)(pte_phy | KERNEL_VIRT_BASE);
    for (int i = 0; i < 512; i++) {
        if (pte[i]) {
            void* page = (void*)((pte[i] & ~0xFFF) | KERNEL_VIRT_BASE);
            page_free(page);
        }
    }
    page_free(pte);
}

void page_reclaim_pmd(uint64_t pmd_phy) {
    uint64_t* pmd = (uint64_t*)(pmd_phy | KERNEL_VIRT_BASE);
    for (int i = 0; i < 512; i++) {
        if (pmd[i]) {
            page_reclaim_pte(pmd[i] & ~0xFFF);
        }
    }
    page_free(pmd);
}

void page_reclaim_pud(uint64_t pud_phy) {
    uint64_t* pud = (uint64_t*)(pud_phy | KERNEL_VIRT_BASE);
    for (int i = 0; i < 512; i++) {
        if (pud[i]) {
            page_reclaim_pmd(pud[i] & ~0xFFF);
        }
    }
    page_free(pud);
}

void page_reclaim(uint64_t pgd_phy) {
    uint64_t* pgd = (uint64_t*)(pgd_phy | KERNEL_VIRT_BASE);
    for (int i = 0; i < 512; i++) {
        if (pgd[i]) {
            page_reclaim_pud(pgd[i] & ~0xFFF);
        }
    }
    page_free(pgd);
}