内存分配[五] - Linux中的Slab(2)

static __always_inline void *__do_kmalloc(size_t size, gfp_t flags, ...)
{
    if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
        return NULL;
    struct kmem_cache *cachep = kmalloc_slab(size, flags);
    void * ret = slab_alloc(cachep, flags, ...);

    return ret;
}

第一级分配

struct array_cache __percpu *cpu_cache;struct array_cache {
    unsigned int avail;
    unsigned int limit;
    void *entry[]; 
};

void *____cache_alloc(struct kmem_cache *cachep, gfp_t flags)
{
    void *objp;

    struct array_cache *ac = cpu_cache_get(cachep);
    if (likely(ac->avail)) {
        objp = ac->entry[--ac->avail];
        return objp;
    }

    objp = cache_alloc_refill(cachep, flags);
    ...
}

第二级分配

• 全部分配完，没有空闲objects的full slabs。

• 分配了一部分，尚有部分空闲的partial slabs。
• 完全空闲可用的free slabs。

struct kmem_cache_node *node[MAX_NUMNODES];

struct kmem_cache_node {
    struct list_head slabs_partial; 
    struct list_head slabs_full;
    struct list_head slabs_free;
    ...
}

第三级分配

void ___cache_free(struct kmem_cache *cachep, void *objp, ..)
{
    struct array_cache *ac = cpu_cache_get(cachep);

    if (ac->avail >= ac->limit) {
        // 归还到对应的slab
        cache_flusharray(cachep, ac);
    }

    ac->entry[ac->avail++] = objp;
}

void kfree(const void *objp)
{
    struct kmem_cache *c = virt_to_cache(objp);
    __cache_free(c, (void *)objp, _RET_IP_);
    ...
}

struct kmem_cache *virt_to_cache(const void *obj)
{
    struct page *page = virt_to_head_page(obj);
    return page->slab_cache;
}

struct page *virt_to_head_page(const void *x)
{
    // object所在的page frame
    struct page *page = virt_to_page(x);
    // 所在compound page的head page
    return compound_head(page);
}

size_t __ksize(const void *objp)
{
    struct kmem_cache *c= virt_to_cache(objp);
    size_t size = c ? c->object_size : 0;
}