nudt-compiler-cpp/xv6-labs/kernel/kalloc.c

// Physical memory allocator, for user processes,
// kernel stacks, page-table pages,
// and pipe buffers. Allocates whole 4096-byte pages.

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "riscv.h"
#include "defs.h"

void freerange(void *pa_start, void *pa_end);
int count=0;

extern char end[]; // first address after kernel.
                   // defined by kernel.ld.

struct run {
  struct run *next;
};

struct {
  struct spinlock lock;
  struct run *freelist;
} kmem;

struct {
  struct spinlock lock;
  int cnt[PHYSTOP / PGSIZE];
}ref;

void
kinit()
{
  initlock(&kmem.lock, "kmem");
  initlock(&ref.lock,"ref");
  freerange(end, (void*)PHYSTOP);
}

void
freerange(void *pa_start, void *pa_end)
{
  char *p;
  p = (char*)PGROUNDUP((uint64)pa_start);
  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE)
  {
    krefset((uint64)p,1);
    //setaccess((uint64)p,1);
    kfree(p);
  }
}

// Free the page of physical memory pointed at by pa,
// which normally should have been returned by a
// call to kalloc().  (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(void *pa)
{
  struct run *r;

  if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
    panic("kfree");

  int count=krefgetbefore((uint64)pa);
  if (count<=0)
    panic("kfree:refree");

  if (count==1)
  {
  // Fill with junk to catch dangling refs.
  //krefsub((uint64)pa);
  //if(ref.cnt[(uint64)pa/PGSIZE]==0){
    memset(pa, 1, PGSIZE);
    r = (struct run*)pa;

    acquire(&kmem.lock);
    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.
void *
kalloc(void)
{
  struct run *r;

  acquire(&kmem.lock);
  r = kmem.freelist;
  if(r)
    kmem.freelist = r->next;
  release(&kmem.lock);

  if(r)
  {
    memset((char*)r, 5, PGSIZE); // fill with junk
    krefadd((uint64)r);
  }

  return (void*)r;
}

void krefadd(uint64 pa)
{
  acquire(&ref.lock);
  ref.cnt[GETPGRANK(pa)] += 1;
  release(&ref.lock);
}

void krefsub(uint64 pa)
{
  acquire(&ref.lock);
  ref.cnt[GETPGRANK(pa)] -= 1;
  release(&ref.lock);
}

int krefget(uint64 pa)
{
  int refcnt = 0;
  acquire(&ref.lock);
  refcnt = ref.cnt[GETPGRANK(pa)];
  release(&ref.lock);
  return refcnt;
}

int krefgetbefore(uint64 pa)
{
  int refcnt = 0;
  acquire(&ref.lock);
  refcnt = ref.cnt[GETPGRANK(pa)];
  ref.cnt[GETPGRANK(pa)] -= 1;
  release(&ref.lock);
  return refcnt;
}

void krefset(uint64 pa,int num)
{
  acquire(&ref.lock);
  ref.cnt[GETPGRANK(pa)] = num;
  release(&ref.lock);
}
/*
void krefprint(void) {
  acquire(&ref.lock);
  for (int i = 0; i < PHYSTOP / PGSIZE; i++) {
    if (ref.cnt[i] > 0) {
      printf("Page %d: %d\n", i, ref.cnt[i]);
    }
  }
  release(&ref.lock);
}*/