1. SWE3015 Operating System Project Assignment 2 박은수, 박경원, 김지원
Demand Paging
SWE3015 Operating System Project
Assignment 2
박은수, 박경원, 김지원

2. Contents
Concept
Example
Path

3. Demand Paging Concept http://csl.skku.edu/SWE3004S13/Overview
When you need memory additionally, the demand paging allocates just VMA. And when you access them, it makes page-fault which allocates real physical memory.

4. Example: malloc() Example
User level function for memory allocation only uses mmap() or brk() which don’t allocate physical memory but just virtual memory area.
<※If the page which has been tried to access is not present, page fault handler allocates physical page : Demand paging>

5. Path do_page_fault(), __do_page_fault()
handle_mm_fault(), __handle_mm_fault()
handle_pte_fault()
There are 5 functions to get the demand page in page-fault.

6. /linux-3.13/arch/x86/mm/fault.c
do_page_fault(struct pt_regs *regs, unsigned long error_code) {}
L.1253:
__do_page_fault(regs, error_code);
/linux-3.13/arch/x86/mm/fault.c

7. /linux-3.13/arch/x86/mm/fault.c
unlikely(kmmio_fault(regs, address))
L.1058:
unlikely(fault_in_kernel_space(address))
L.1084:
unlikely(kprobes_fault(regs))
L.1090:
static_cpu_has(X86_FEATURE_SMAP)
L.1091:
unlikely(smap_violation(error_code, regs))
L.1101:
unlikely(in_atomic() || !mm)
L.1143:
unlikely(!down_read_trylock(&mm->mmap_sem))
L.1161:
unlikely(!vma)
L.1144:
(error_code & PF_USER) == 0 && !search_exception_tables(regs->ip)
L.1165:
likely(vma->vm_start <= address)
L.1167:
unlikely(!(vma->vm_flags & VM_GROWSDOWN))
L.1171:
error_code & PF_USER
L.1193:
unlikely(access_error(error_code, vma))
L.1178:
unlikely(address * sizeof(unsigned long) < regs->sp)
L.1183:
unlikely(expand_stack(vma, address))
L.1019:
__do_page_fault(struct pt_regs *regs, unsigned long error_code) {}
L.1203:
handle_mm_fault(mm, vma, address, flags);
False
True
/linux-3.13/arch/x86/mm/fault.c

8. __handle_mm_fault(mm, vma, address, flags);
handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags) {}
L.3803:
__handle_mm_fault(mm, vma, address, flags);
/linux-3.13/mm/memory.c

9. /linux-3.13/mm/memory.c L.3692:
unlikely(is_vm_hugetlb_page(vma))
L.3706:
!pud
L.3709:
!pmd
L.3711:
pmd_none(*pmd) && transparent_hugepage_enabled(vma)
L.3716:
!(ret & VM_FAULT_FALLBACK)
L.3723:
pmd_trans_huge(orig_pmd)
L.3766:
unlikely(pmd_none(*pmd)) && unlikely(__pte_alloc(mm, vma, pmd, address))
L.3770:
unliely(pmd_trans_huge(*pmd))
L.3692:
__handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags) {}
L.3778:
handle_pte_fault(mm, vma, address, pte, pmd, flags);
False
True
/linux-3.13/mm/memory.c

10. /linux-3.13/mm/memory.c (+ do_anonymous_page: allocate free page,
!pte_present(entry)
L.3633:
handle_pte_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, pte_t *pte, pmd_t *pmd, unsigned int flags) {}
/* Demand Paging */
True
/linux-3.13/mm/memory.c
(+ do_anonymous_page: allocate free page,
do_swap_page: swap in)

11. Q & A