内核内存管理

作者：朱涵俊
链接：https://zhuanlan.zhihu.com/p/140274586
来源：知乎
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内存管理分为虚拟地址空间管理，物理内存管理，内核堆栈管理。

内核在启动的过程中需要不断申请内存，这些内存申请之后一般就不需要释放。频繁的申请释放会导致内存碎片，性能下降。因此内核堆kheap管理的原则是申请一次，终身使用。堆内存分为2类，一是小内存，而是页对齐的内存。因为有的内核对象需要页对齐，比如页表。

kernel/kheap.c

//由于只申请不释放，不会有很多内存块。主要是BIOS，内核数据等引起的。
#define MAX_HEAP_HOLE   10
#define MAX_SMALL_HOLE  100
#if 1
#define DEBUG_PRINT printk
#else
#define DEBUG_PRINT inline_printk
#endif
 
struct kheap_t;
struct kheap_t {
    ulong addr;
    ulong size;
    ulong orgin_size;
    struct kheap_t *pnext;
};
static struct kheap_t *pfree4k;
static struct kheap_t *phead4k;
static struct kheap_t heap_holes[MAX_HEAP_HOLE];
static struct kheap_t heap_small_holes[MAX_SMALL_HOLE];
__thread static spinlock_t spin_4k;
__thread static spinlock_t spin_small;
static struct kheap_t *pfree_small;
static struct kheap_t *phead_small;
void init_kheap()
{
    for (int i = 0; i < MAX_HEAP_HOLE - 1; i++) {
        heap_holes[i].pnext = &heap_holes[i + 1];
    }
    heap_holes[MAX_HEAP_HOLE - 1].pnext = 0;
    pfree4k = heap_holes;
    phead4k = 0;
    init_spinlock(&spin_4k);
 
    for (int i = 0; i < MAX_SMALL_HOLE - 1; i++) {
        heap_small_holes[i].pnext = &heap_small_holes[i + 1];
    }
    heap_small_holes[MAX_SMALL_HOLE - 1].pnext = 0;
    pfree_small = heap_small_holes;
    phead_small = 0;
    init_spinlock(&spin_small);
 
}
void free_kheap_4k(ulong addr, ulong size)
{
    struct kheap_t *p;
    struct kheap_t *ph;
 
    ASSERT((addr & 0xfff) == 0 && (size & 0xfff) == 0); //4k aligned
 
    p = pfree4k;
    if (!p) {
        panic("MAX_HEAP_HOLE too small!\n");
    }
    spin_lock(&spin_4k);
    pfree4k = pfree4k->pnext;
    p->addr = addr;
    p->orgin_size = size;
    p->size = size;
    //sort by addr asc,early init can only use low kheap
    if (!phead4k || phead4k->addr > p->addr) {
        p->pnext = phead4k;
        phead4k = p;
        spin_unlock(&spin_4k);
       return;
    }
 
    ph = phead4k;
    while (ph->pnext && ph->pnext->addr < p->addr) {
        ph = ph->pnext;
    }
    p->pnext = ph->pnext;
    ph->pnext = p;