// 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);
uint64 getRefIdx(uint64 pa);

struct spinlock reference_lock;  // 加锁
int pm_reference[(PHYSTOP - KERNBASE)/PGSIZE];  // 记录物理页的引用计数

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

// va映射为idx
uint64
getRefIdx(uint64 pa)
{
  return (pa-KERNBASE)/PGSIZE;
}


struct run {
  struct run *next;
};

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

void
kinit()
{
  initlock(&kmem.lock, "kmem");
  initlock(&reference_lock, "pm_reference");
  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)
    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");

  acquire(&reference_lock);
  pm_reference[getRefIdx((uint64)pa)] --;
  if(pm_reference[getRefIdx((uint64)pa)] <= 0){
    // Fill with junk to catch dangling refs.
    memset(pa, 1, PGSIZE);
    r = (struct run*)pa;
    acquire(&kmem.lock);
    r->next = kmem.freelist;
    kmem.freelist = r;
    release(&kmem.lock);
  }

  release(&reference_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
    pm_reference[getRefIdx((uint64) r)] = 1;
  }
  return (void*)r;
}

// reference操作
void
reference_operation(void* pa, int op)
{
  acquire(&reference_lock);
  if(op) pm_reference[getRefIdx((uint64)pa)]++;
  else pm_reference[getRefIdx((uint64)pa)]--;
  release(&reference_lock);
}

void*
cowcopy_pa(void* pa){
  acquire(&reference_lock);
  if(pm_reference[getRefIdx((uint64)pa)] <= 1){
    release(&reference_lock);
    return pa;
  }

  char* new = kalloc();
  if(new == 0){
    release(&reference_lock);
    panic("out of memory");
    return 0;
  }

  memmove((void*)new, pa, PGSIZE);

  // 变更引用计数
  pm_reference[getRefIdx((uint64)pa)] --;
  release(&reference_lock);
  return (void*)new;
}