MIT 6.S081 Operating System Enginerring Lab5 Lazy allocation
这里给出Lab5 Lazy allocation的解析。
学习资料：
- https://pdos.csail.mit.edu/6.828/2020/schedule.html
- https://mit-public-courses-cn-translatio.gitbook.io/mit6-s081/
- https://th0ar.gitbooks.io/xv6-chinese/content/
- https://www.bilibili.com/video/BV19k4y1C7kA?p=6
参考资料：
- https://github.com/PKUFlyingPig/MIT6.S081-2020fall/tree/master/reports
- https://fanxiao.tech/posts/MIT-6S081-notes/
- https://www.bilibili.com/video/BV19k4y1C7kA?p=6
Eliminate allocation from sbrk() (easy)
修改xv6-labs-2020/kernel/sysproc.c/sys_sbrk，这里只更新sz的大小即可：
uint64
sys_sbrk(void)
{
int addr;
int n;
if(argint(0, &n) < 0)
return -1;
addr = myproc()->sz;
// if(growproc(n) < 0)
// return -1;
// part 1 begin
myproc()->sz += n;
// part 1 end
return addr;
}测试：
make qemu
$ echo hi
page fault 0x0000000000004008
page fault 0x0000000000013f48
panic: uvmunmap: not mappedLazy allocation (moderate)
修改xv6-labs-2020/kernel/trap.c/usertrap，当Load page fault, Store/AMO page fault错误产生时申请页面：
//
// handle an interrupt, exception, or system call from user space.
// called from trampoline.S
//
void
usertrap(void)
{
int which_dev = 0;
if((r_sstatus() & SSTATUS_SPP) != 0)
panic("usertrap: not from user mode");
// send interrupts and exceptions to kerneltrap(),
// since we're now in the kernel.
w_stvec((uint64)kernelvec);
struct proc *p = myproc();
// save user program counter.
p->trapframe->epc = r_sepc();
if(r_scause() == 8){
// system call
if(p->killed)
exit(-1);
// sepc points to the ecall instruction,
// but we want to return to the next instruction.
p->trapframe->epc += 4;
// an interrupt will change sstatus &c registers,
// so don't enable until done with those registers.
intr_on();
syscall();
} else if((which_dev = devintr()) != 0){
// ok
}
// part 2 begin
// Load page fault, Store/AMO page fault
else if ((r_scause() == 13) || (r_scause() == 15)) {
// 返回出错的虚拟地址
uint64 va = r_stval();
printf("page fault %p\n", va);
uint64 ka = (uint64) kalloc();
if (ka == 0) {
p->killed = 1;
} else {
memset((void*)ka, 0, PGSIZE);
va = PGROUNDDOWN(va);
if(mappages(p->pagetable, va, PGSIZE, ka, PTE_W|PTE_R|PTE_U) != 0) {
kfree((void*)ka);
p->killed = 1;
}
}
}
// part 2 end
else {
printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
printf(" sepc=%p stval=%p\n", r_sepc(), r_stval());
p->killed = 1;
}
if(p->killed)
exit(-1);
// give up the CPU if this is a timer interrupt.
if(which_dev == 2)
yield();
usertrapret();
}修改xv6-labs-2020/kernel/vm.c，跳过报错：
// Remove npages of mappings starting from va. va must be
// page-aligned. The mappings must exist.
// Optionally free the physical memory.
void
uvmunmap(pagetable_t pagetable, uint64 va, uint64 npages, int do_free)
{
uint64 a;
pte_t *pte;
if((va % PGSIZE) != 0)
panic("uvmunmap: not aligned");
for(a = va; a < va + npages*PGSIZE; a += PGSIZE){
if((pte = walk(pagetable, a, 0)) == 0)
panic("uvmunmap: walk");
// if((*pte & PTE_V) == 0)
// panic("uvmunmap: not mapped");
// part 2 begin
// 跳过报错
if((*pte & PTE_V) == 0) {
continue;
}
// part 2 end
if(PTE_FLAGS(*pte) == PTE_V)
panic("uvmunmap: not a leaf");
if(do_free){
uint64 pa = PTE2PA(*pte);
kfree((void*)pa);
}
*pte = 0;
}
}测试：
make qemu
$ echo hi
page fault 0x0000000000004008
page fault 0x0000000000013f48
hiLazytests and Usertests (moderate)
修改xv6-labs-2020/kernel/sysproc.c/sys_sbrk，在负数情形直接使用growproc部分的代码进行处理：
uint64
sys_sbrk(void)
{
int addr;
int n;
if(argint(0, &n) < 0)
return -1;
addr = myproc()->sz;
// if(growproc(n) < 0)
// return -1;
// // part 1 begin
// myproc()->sz += n;
// // part 1 end
// part 3 begin
if (n >= 0) {
myproc()->sz += n;
} else {
// n < 0时直接删除映射
uint sz = myproc()->sz;
myproc()->sz = uvmdealloc(myproc()->pagetable, sz, sz + n);
}
// part 3 end
return addr;
}修改xv6-labs-2020/kernel/trap.c/usertrap，增加判断va地址是否合法的部分：
//
// handle an interrupt, exception, or system call from user space.
// called from trampoline.S
//
void
usertrap(void)
{
int which_dev = 0;
if((r_sstatus() & SSTATUS_SPP) != 0)
panic("usertrap: not from user mode");
// send interrupts and exceptions to kerneltrap(),
// since we're now in the kernel.
w_stvec((uint64)kernelvec);
struct proc *p = myproc();
// save user program counter.
p->trapframe->epc = r_sepc();
if(r_scause() == 8){
// system call
if(p->killed)
exit(-1);
// sepc points to the ecall instruction,
// but we want to return to the next instruction.
p->trapframe->epc += 4;
// an interrupt will change sstatus &c registers,
// so don't enable until done with those registers.
intr_on();
syscall();
} else if((which_dev = devintr()) != 0){
// ok
}
// part 3 begin
// page fault
else if ((r_scause() == 13) || (r_scause() == 15)) {
// 返回出错的虚拟地址
uint64 va = r_stval();
// 不能添加printf, 否则答案不正确
// va地址>=p->sz, 或<stack
if ((va >= p->sz) || (va < p->trapframe->sp)) {
p->killed = 1;
} else {
uint64 ka = (uint64) kalloc();
if (ka == 0) {
p->killed = 1;
} else {
memset((void*)ka, 0, PGSIZE);
va = PGROUNDDOWN(va);
if(mappages(p->pagetable, va, PGSIZE, ka, PTE_W|PTE_R|PTE_U) != 0) {
kfree((void*)ka);
p->killed = 1;
}
}
}
}
// part 3 end
else {
printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
printf(" sepc=%p stval=%p\n", r_sepc(), r_stval());
p->killed = 1;
}
if(p->killed)
exit(-1);
// give up the CPU if this is a timer interrupt.
if(which_dev == 2)
yield();
usertrapret();
}接着修改vm.c函数，注意需要查看实验中提到的fork, read, write函数调用了哪些内存相关的函数：
fork -> uvmcopy
read -> sys_read -> fileread -> piperead -> copyout
write -> sys_write -> filewrite -> pipewrite -> copyin在vm.c一开始添加：
// part 3 begin
#include "spinlock.h"
#include "proc.h"
// part 3 end修改uvmunmap：
// Remove npages of mappings starting from va. va must be
// page-aligned. The mappings must exist.
// Optionally free the physical memory.
void
uvmunmap(pagetable_t pagetable, uint64 va, uint64 npages, int do_free)
{
uint64 a;
pte_t *pte;
if((va % PGSIZE) != 0)
panic("uvmunmap: not aligned");
for(a = va; a < va + npages*PGSIZE; a += PGSIZE){
// part 3 begin
if((pte = walk(pagetable, a, 0)) == 0) {
continue;
}
if((*pte & PTE_V) == 0) {
continue;
}
// part 3 end
if(PTE_FLAGS(*pte) == PTE_V)
panic("uvmunmap: not a leaf");
if(do_free){
uint64 pa = PTE2PA(*pte);
kfree((void*)pa);
}
*pte = 0;
}
}修改uvmcopy：
// Given a parent process's page table, copy
// its memory into a child's page table.
// Copies both the page table and the
// physical memory.
// returns 0 on success, -1 on failure.
// frees any allocated pages on failure.
int
uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
{
pte_t *pte;
uint64 pa, i;
uint flags;
char *mem;
for(i = 0; i < sz; i += PGSIZE){
// part 3 begin
if((pte = walk(old, i, 0)) == 0) {
continue;
}
if((*pte & PTE_V) == 0) {
continue;
}
// part 3 end
pa = PTE2PA(*pte);
flags = PTE_FLAGS(*pte);
if((mem = kalloc()) == 0)
goto err;
memmove(mem, (char*)pa, PGSIZE);
if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
kfree(mem);
goto err;
}
}
return 0;
err:
uvmunmap(new, 0, i / PGSIZE, 1);
return -1;
}copyin，copyout：
// Copy from kernel to user.
// Copy len bytes from src to virtual address dstva in a given page table.
// Return 0 on success, -1 on error.
int
copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
{
uint64 n, va0, pa0;
// part 3 begin
struct proc *p = myproc();
// part 3 end
while(len > 0){
va0 = PGROUNDDOWN(dstva);
pa0 = walkaddr(pagetable, va0);
// part 3 begin
if (pa0 == 0) {
if ((va0 >= p->sz) || (va0 < p->trapframe->sp)) {
return -1;
} else {
pa0 = (uint64)kalloc();
if (pa0 == 0) {
p->killed = 1;
} else {
memset((void *)pa0, 0, PGSIZE);
va0 = PGROUNDDOWN(va0);
if(mappages(p->pagetable, va0, PGSIZE, pa0, PTE_W|PTE_R|PTE_U) != 0) {
kfree((void *)pa0);
p->killed = 1;
}
}
}
}
// part 3 end
n = PGSIZE - (dstva - va0);
if(n > len)
n = len;
memmove((void *)(pa0 + (dstva - va0)), src, n);
len -= n;
src += n;
dstva = va0 + PGSIZE;
}
return 0;
}
// Copy from user to kernel.
// Copy len bytes to dst from virtual address srcva in a given page table.
// Return 0 on success, -1 on error.
int
copyin(pagetable_t pagetable, char *dst, uint64 srcva, uint64 len)
{
uint64 n, va0, pa0;
// part 3 begin
struct proc *p = myproc();
// part 3 end
while(len > 0){
va0 = PGROUNDDOWN(srcva);
pa0 = walkaddr(pagetable, va0);
// part 3 begin
if (pa0 == 0) {
if ((va0 >= p->sz) || (va0 < p->trapframe->sp)) {
return -1;
} else {
pa0 = (uint64) kalloc();
if (pa0 == 0) {
p->killed = 1;
} else {
memset((void *)pa0, 0, PGSIZE);
va0 = PGROUNDDOWN(va0);
if(mappages(p->pagetable, va0, PGSIZE, pa0, PTE_W|PTE_R|PTE_U) != 0) {
kfree((void *)pa0);
p->killed = 1;
}
}
}
}
// part 3 end
n = PGSIZE - (srcva - va0);
if(n > len)
n = len;
memmove(dst, (void *)(pa0 + (srcva - va0)), n);
len -= n;
dst += n;
srcva = va0 + PGSIZE;
}
return 0;
}测试1：
./grade-lab-lazy lazytests
== Test running lazytests == (1.0s)测试2：
./grade-lab-lazy usertests
== Test usertests == (136.4s)
== Test usertests: pgbug ==
usertests: pgbug: OK
== Test usertests: sbrkbugs ==
usertests: sbrkbugs: OK
== Test usertests: argptest ==
usertests: argptest: OK
== Test usertests: sbrkmuch ==
usertests: sbrkmuch: OK
== Test usertests: sbrkfail ==
usertests: sbrkfail: OK
== Test usertests: sbrkarg ==
usertests: sbrkarg: OK
== Test usertests: stacktest ==
usertests: stacktest: OK
== Test usertests: execout ==
usertests: execout: OK
== Test usertests: copyin ==
usertests: copyin: OK
== Test usertests: copyout ==
usertests: copyout: OK
== Test usertests: copyinstr1 ==
usertests: copyinstr1: OK
== Test usertests: copyinstr2 ==
usertests: copyinstr2: OK
== Test usertests: copyinstr3 ==
usertests: copyinstr3: OK
== Test usertests: rwsbrk ==
usertests: rwsbrk: OK
== Test usertests: truncate1 ==
usertests: truncate1: OK
== Test usertests: truncate2 ==
usertests: truncate2: OK
== Test usertests: truncate3 ==
usertests: truncate3: OK
== Test usertests: reparent2 ==
usertests: reparent2: OK
== Test usertests: badarg ==
usertests: badarg: OK
== Test usertests: reparent ==
usertests: reparent: OK
== Test usertests: twochildren ==
usertests: twochildren: OK
== Test usertests: forkfork ==
usertests: forkfork: OK
== Test usertests: forkforkfork ==
usertests: forkforkfork: OK
== Test usertests: createdelete ==
usertests: createdelete: OK
== Test usertests: linkunlink ==
usertests: linkunlink: OK
== Test usertests: linktest ==
usertests: linktest: OK
== Test usertests: unlinkread ==
usertests: unlinkread: OK
== Test usertests: concreate ==
usertests: concreate: OK
== Test usertests: subdir ==
usertests: subdir: OK
== Test usertests: fourfiles ==
usertests: fourfiles: OK
== Test usertests: sharedfd ==
usertests: sharedfd: OK
== Test usertests: exectest ==
usertests: exectest: OK
== Test usertests: bigargtest ==
usertests: bigargtest: OK
== Test usertests: bigwrite ==
usertests: bigwrite: OK
== Test usertests: bsstest ==
usertests: bsstest: OK
== Test usertests: sbrkbasic ==
usertests: sbrkbasic: OK
== Test usertests: kernmem ==
usertests: kernmem: OK
== Test usertests: validatetest ==
usertests: validatetest: OK
== Test usertests: opentest ==
usertests: opentest: OK
== Test usertests: writetest ==
usertests: writetest: OK
== Test usertests: writebig ==
usertests: writebig: OK
== Test usertests: createtest ==
usertests: createtest: OK
== Test usertests: openiput ==
usertests: openiput: OK
== Test usertests: exitiput ==
usertests: exitiput: OK
== Test usertests: iput ==
usertests: iput: OK
== Test usertests: mem ==
usertests: mem: OK
== Test usertests: pipe1 ==
usertests: pipe1: OK
== Test usertests: preempt ==
usertests: preempt: OK
== Test usertests: exitwait ==
usertests: exitwait: OK
== Test usertests: rmdot ==
usertests: rmdot: OK
== Test usertests: fourteen ==
usertests: fourteen: OK
== Test usertests: bigfile ==
usertests: bigfile: OK
== Test usertests: dirfile ==
usertests: dirfile: OK
== Test usertests: iref ==
usertests: iref: OK
== Test usertests: forktest ==
usertests: forktest: OK 本博客所有文章除特别声明外，均采用 CC BY-NC-SA 4.0 许可协议。转载请注明来自 Doraemonzzz！
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