Linux Slab分配器(3)-创建缓存-Linux-爱易网页

Linux Slab分配器(3)-创建缓存

日期：2014-05-16　浏览次数：20747 次

Linux Slab分配器(三)--创建缓存

创建新的缓存必须通过kmem_cache_create()函数来完成，原型如下

struct kmem_cache *
kmem_cache_create (const char *name, size_t size, size_t align,
	unsigned long flags, void (*ctor)(void *))

name:所创建的新缓存的名字
size :缓存所分配对象的大小
align:对象的对齐值
flags:创建用的标识
ctor:创建对象时的构造函数

kmem_cache_create()的实际工作就是为新的缓存申请缓存描述符，array_cache描述符和kmem_list3描述符，并根据接收的参数对这三个结构中的变量进行相应的初始化。新创建的缓存是空的，不包含slab。

struct kmem_cache *
kmem_cache_create (const char *name, size_t size, size_t align,
	unsigned long flags, void (*ctor)(void *))
{
	size_t left_over, slab_size, ralign;
	struct kmem_cache *cachep = NULL, *pc;
	gfp_t gfp;

	/*
	 * Sanity checks... these are all serious usage bugs.
	 */
	 /*做一些必要的检查，以下情况都是不合法的:
	   1.缓存名为空
	   2.处于中断环境中
	   3.缓存中的对象大小小于处理器的字长
	   4.缓存中的对象大小大于普通缓存的最大长度*/
	if (!name || in_interrupt() || (size < BYTES_PER_WORD) ||
	    size > KMALLOC_MAX_SIZE) {
		printk(KERN_ERR "%s: Early error in slab %s\n", __func__,
				name);
		BUG();
	}

	/*
	 * We use cache_chain_mutex to ensure a consistent view of
	 * cpu_online_mask as well.  Please see cpuup_callback
	 */
	if (slab_is_available()) {
		get_online_cpus();
		mutex_lock(&cache_chain_mutex);
	}

	list_for_each_entry(pc, &cache_chain, next) {
		char tmp;
		int res;

		/*
		 * This happens when the module gets unloaded and doesn't
		 * destroy its slab cache and no-one else reuses the vmalloc
		 * area of the module.  Print a warning.
		 */
		res = probe_kernel_address(pc->name, tmp);
		if (res) {
			printk(KERN_ERR
			       "SLAB: cache with size %d has lost its name\n",
			       pc->buffer_size);
			continue;
		}

		if (!strcmp(pc->name, name)) {
			printk(KERN_ERR
			       "kmem_cache_create: duplicate cache %s\n", name);
			dump_stack();
			goto oops;
		}
	}

#if DEBUG
	WARN_ON(strchr(name, ' '));	/* It confuses parsers */
#if FORCED_DEBUG
	/*
	 * Enable redzoning and last user accounting, except for caches with
	 * large objects, if the increased size would increase the object size
	 * above the next power of two: caches with object sizes just above a
	 * power of two have a significant amount of internal fragmentation.
	 */
	if (size < 4096 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN +
						2 * sizeof(unsigned long long)))
		flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
	if (!(flags & SLAB_DESTROY_BY_RCU))
		flags |= SLAB_POISON;
#endif
	if (flags & SLAB_DESTROY_BY_RCU)
		BUG_ON(flags & SLAB_POISON);
#endif
	/*
	 * Always checks flags, a caller might be expecting debug support which
	 * isn't available.
	 */
	BUG_ON(flags & ~CREATE_MASK);

	/*
	 * Check that size is in terms of words.  This is needed to avoid
	 * unaligned accesses for some archs when redzoning is used, and makes
	 * sure any on-slab bufctl's are also correctly aligned.
	 */
	 /*如果缓存对象大小没有对齐到处理器字长，则对齐之*/
	if (size & (BYTES_PER_WORD - 1)) {
		size += (BYTES_PER_WORD - 1);
		size &= ~(BYTES_PER_WORD - 1);
	}

	/* calculate the final buffer alignment: */

	/* 1) arch recommendation: can be overridden for debug */
	/*要求按照体系结构对齐*/
	if (flags & SLAB_HWCACHE_ALIGN) {
		/*
		 * Default alignment: as specified by the arch code.  Except if
		 * an object is really small, then squeeze multiple objects into
		 * one cacheline.
		 */
		ralign = cache_line_size();/*对齐值取L1缓存行的大小*/
		/*如果对象大小足够小，则不断压缩对齐值以保证能将足够多的对象装入一个缓存行*/
		while (size <= ralign / 2)
			ralign /= 2;
	} else {
		ralign = BYTES_PER_WORD; /*对齐值取处理器字长*/
	}

	/*
	 * Redzoning and user store require word alignment or possi


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