// Physical memory allocator, intended to allocate // memory for user processes, kernel stacks, page table pages, // and pipe buffers. Allocates 4096-byte pages. #include "types.h" #include "defs.h" #include "param.h" #include "mmu.h" #include "spinlock.h" struct run { struct run *next; }; struct { struct spinlock lock; struct run *freelist; } kmem; extern char end[]; // first address after kernel loaded from ELF file // Initialize free list of physical pages. void kinit(void) { char *p; initlock(&kmem.lock, "kmem"); p = (char*)PGROUNDUP((uint)end); for(; p + PGSIZE - 1 < (char*)PHYSTOP; p += PGSIZE) kfree(p); } //PAGEBREAK: 21 // Free the page of physical memory pointed at by v, // which normally should have been returned by a // call to kalloc(). (The exception is when // initializing the allocator; see kinit above.) void kfree(char *v) { struct run *r; if((uint)v % PGSIZE || v < end || (uint)v >= PHYSTOP) panic("kfree"); // Fill with junk to catch dangling refs. memset(v, 1, PGSIZE); acquire(&kmem.lock); r = (struct run*)v; r->next = kmem.freelist; kmem.freelist = r; release(&kmem.lock); } // Allocate one 4096-byte page of physical memory. // Returns a pointer that the kernel can use. // Returns 0 if the memory cannot be allocated. char* kalloc(void) { struct run *r; acquire(&kmem.lock); r = kmem.freelist; if(r) kmem.freelist = r->next; release(&kmem.lock); return (char*)r; }