1. Memory Management in Linux David Chang OS Lab., NCTU,Taiwan

2. Agenda Initialization Page Fault Handling Page Cache and Swap Cache Swap Area Management Copying Virtual Address Spaces

3. Initialization paging_init() –set up the page tables to map in all the available physical memory –Kernel has the virtual address from 3G~4G –physical address = virtual address - 3G (see figure) free_area_init() –allocate and initialize the page structures Linux use a page structure for one physical page all page structures are marked as DMAable and RESERVED –allocate and initialize the swap cache and free area list

4. Address Mapping in Kernel Virtual address Physical address 0 3G 4G E.g. 16M

5. Initialization mem_init() –fixup the page structures and make all the available pages free….

6. Page Fault Handling do_page_fault() –this routine is a dispatcher that is invoked when page fault occurs –Works: find out the faulting address find out the reason for the fault and call the right routine –protection fault: do_wp_page() –page-not-present fault: do_no_page()

7. Page Fault Handling do_wp_page() –handle write protection fault –Copy-On-Write if necessary do_no_page() –used to page-in a page – determine the source of the page Executable file? Swap area ? Or Anonymous page?

8. Page Fault Handling Page-in from an executable file –When an executable file is opened, Linux will attach the file operations for the file. The file operations include a mmap( ) function –For UFS, this mmap() function points to generic_file_mmap( ) –After opening the file, Linux maps segments by do_mmap( ) –do_mmap() will actually call the mmap() file operation to attach the vm_operations for the vma –The vm operation contains a nopage( ) which is called when page fault occurs( see filemap_nopage() )

9. Page Fault Handling do_mmap() –construct a vma –insert the vma->vm_op by calling file->f_op->mmap() –brings in pages if VM_LOCKED is specified filemap_nopage() –look for the page from page cache first –read-in the page if cache miss –read-ahead if necessary

10. Swap Area Management do_swap_page() –determine if the vma that contains the faulting page has swapin() vm_operation –call swap_in() if the vma doesn’t have swapin() vm operation swap_in() –the default swap in operation: allocate a free page and get the content of the page from the swap area –de-allocate the swap page in swap area!!!!!!!

11. Swap Area Organization swap_info lockmap A swap area 1111111111111… 111……………… 111……00000000 00SWAP-SPACE

12. Swap Area Management swap_on() –enable a swap area –allocate pages for lockmap and swapmap –insert the swap area into the swap list

13. Copying Virtual Address Spaces When Linux create a new process by fork(), it will call copy_mm() to copy the address space from the father to the child. The child can share the same address space with its father if the CLONE_VM is specified copy_mm() –new_page_tables( ) allocate a page for PTEs and copy the kernel-part PTEs –dup_mmap( ) duplicate the mmap