MIT6.S081 Lab5: xv6 lazy page allocation

Eliminate allocation from sbrk()

1. 更改kernel/sysproc.c中的sys_sbrk函数：

   uint64
   sys_sbrk(void)
   {
        
       int addr;
       int n;
   
       if(argint(0, &n) < 0)
           return -1;
       addr = myproc()->sz;
       /* if(growproc(n) < 0)
           return -1; */
       myproc()->sz += n;
   
       return addr;
   }
   

Lazy allocation

1. 修改kernel/trap.c中的usertrap函数：

   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
   } else if(r_scause() == 13 || r_scause() == 15) {
        
       mappages(p->pagetable, PGROUNDDOWN(r_stval()), PGSIZE, (uint64)kalloc(), PTE_U|PTE_W|PTE_R|PTE_X);
   } 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;
   }
   

Lazytests and Usertests

1. 修改kernel/sysproc.c中的sys_sbrk函数：

   uint64
   sys_sbrk(void)
   {
        
       int addr;
       int n;
       uint64 newaddr;
   
       if(argint(0, &n) < 0)
           return -1;
       addr = myproc()->sz;
       newaddr = myproc()->sz + n;
   
       if(newaddr >= MAXVA)
           return addr;
   
       if(n < 0) {
        
           if(newaddr > addr) {
        
               newaddr = 0;
               uvmunmap(myproc()->pagetable, 0, PGROUNDUP(addr)/PGSIZE, 1);
           } else
               uvmunmap(myproc()->pagetable, PGROUNDUP(newaddr), (PGROUNDUP(addr)-PGROUNDUP(newaddr))/ PGSIZE, 1);
       }
   
       myproc()->sz += n;
   
       return addr;
   }
   

2. 修改kernel/trap.c中的usertrap函数：

   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
   } else if(r_scause() == 13 || r_scause() == 15) {
        
       uint64 pa = (uint64)kalloc();
       
       if(r_stval() >= p->sz)
           p->killed = 1;
       else if(pa == 0)
           p->killed = 1;
       else if(r_stval()<p->trapframe->sp)
           p->killed = 1;
       else
           mappages(p->pagetable, PGROUNDDOWN(r_stval()), PGSIZE, pa, PTE_U|PTE_W|PTE_R|PTE_X);
   } 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;
   }
   

3. 修改kernel/vm.c：

   #include "spinlock.h"
   #include "proc.h"
   

   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)
               continue; //panic("uvmunmap: walk");
           if((*pte & PTE_V) == 0)
               continue; // panic("uvmunmap: not mapped");
           if(PTE_FLAGS(*pte) == PTE_V)
               panic("uvmunmap: not a leaf");
           if(do_free){
        
               uint64 pa = PTE2PA(*pte);
               kfree((void*)pa);
           }
           *pte = 0;
       }
   }
   

   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){
        
           if((pte = walk(old, i, 0)) == 0)
               continue; // panic("uvmcopy: pte should exist");
           if((*pte & PTE_V) == 0)
               continue; // panic("uvmcopy: page not present");
           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;
   }
   

   int
   copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
   {
        
       uint64 n, va0, pa0;
   
       while(len > 0){
        
           va0 = PGROUNDDOWN(dstva);
           pa0 = walkaddr(pagetable, va0);
           if(pa0 == 0) {
        
               if(dstva >= myproc()->sz)
                   return -1;
               uint64 mem = (uint64)kalloc();
               if(!mem)
                   return -1;
               pa0 = mem;
               memset((void*)mem, 0, PGSIZE);
               mappages(pagetable, va0, PGSIZE, pa0, PTE_R|PTE_W|PTE_U);
           }
           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;
   }
   

   int
   copyin(pagetable_t pagetable, char *dst, uint64 srcva, uint64 len)
   {
        
       uint64 n, va0, pa0;
   
       while(len > 0){
        
           va0 = PGROUNDDOWN(srcva);
           pa0 = walkaddr(pagetable, va0);
           if(pa0 == 0) {
        
               if(srcva >= myproc()->sz)
                   return -1;
               uint64 mem = (uint64)kalloc();
               if(!mem)
                   return -1;
               pa0 = mem;
               memset((void*)mem, 0, PGSIZE);
               mappages(pagetable, va0, PGSIZE, pa0, PTE_R|PTE_W|PTE_U);
           }
           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;
   }