Advanced Operating Systems
COMP9242 2012/S2 |
UNSW
CRICOS Provider Number: 00098G |
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M2: Memory managerThe aim of this milestone is to design and implement simple
frame-based memory management. You will need to set up a frame
table so that you can keep track of the system's physical memory
and the capabilities you have to that memory (cptrs
to Recall in your basic operating systems knowledge that the virtual memory subsystem has to keep track of the address space (or process), virtual address, and physical address of each mapping. It has to translate (process, virtual address) to physical address for virtual address translation, and physical address to (process, virtual address) to invalidate translations for page replacement. With seL4, for each virtual memory mapping between a virtual
page and a physical frame, you must keep track of an additional
cptr, i.e. a reference to a You should review Chapter 6 in the seL4 reference manual to gain some exposure to the seL4 memory management model before proceeding further. You should create a new file
in
Design alternativesSome things you should think of are what information you need to store in the frame table. You may want to take into account the fact that you will later be using this frame table to support virtual memory, swapping and multiple processes. You should take this into account when designing your data structures. You should also take into account which operations you want to perform on the frame table, and the required algorithms to fulfill these. For example, you don't want an order n-square O(n^2) search to find the next free frame. Of course it is easy to change these data structures later as you gain a better understanding of the issues involved, so don't spend too much time designing the perfect structure now. Your design should take into account the space and time complexity and bounds of your data structures. AssessmentThe demonstration of this solution should show the execution of some example code using the allocation routine. For example: /* Allocate 10 pages and make sure you can touch them all */ for (i = 0; i < 10; i++) { /* Allocate a page */ seL4_Word vaddr; frame_alloc(&vaddr); assert(vaddr); /* Test you can touch the page */ *vaddr = 0x37; assert(*vaddr == 0x37); printf("Page #%d allocated at %p\n", i, (void *) vaddr); } /* Test that you eventually run out of memory gracefully, and doesn't crash */ for (;;) { /* Allocate a page */ seL4_Word vaddr; frame_alloc(&vaddr); if (!vaddr) { printf("Out of memory!\n"); break; } /* Test you can touch the page */ *vaddr = 0x37; assert(*vaddr == 0x37); } /* Test that you never run out of memory if you always free frames. This loop should never finish */ for (int i = 0;; i++) { /* Allocate a page */ seL4_Word vaddr; page = frame_alloc(&vaddr); assert(vaddr != 0); /* Test you can touch the page */ *vaddr = 0x37; assert(*vaddr == 0x37); printf("Page #%d allocated at %p\n", i, vaddr); frame_free(page); } You should also be able to explain to the tutor the structure of your frame table, how your code works and any design decisions you took. Last modified: 24 Jul 2012. |