slab分配器 - 实例用法
slab分配器 - 实例用法
其原理此处不再赘述，请参看：http://www.ibm.com/developerworks/cn/linux/l-linux-slab-allocator/
1. 定义一个 kmem_cache 对象，然后对其进行初始化
static struct kmem_cache *sample_cachep;static void init_sample_cachep( void ){ sample_cachep = kmem_cache_create( "sample_cachep", /* Name */ 32, /* Object Size */ 0, /* Alignment */ SLAB_HWCACHE_ALIGN, /* Flags */ NULL); /* Constructor */ return;} 这里是采用的通用slab缓存方式实现，这个特定的缓存包含 32 字节的对象，并且是硬件缓存对齐的（由标志参数 SLAB_HWCACHE_ALIGN 定义）。
如果采用专用slab缓存，那么必须要知道建立缓存对象的大小，比如，我们需要为sample_struct结构体建立一个专用的slab缓存，那么其调用格式如下：
static struct kmem_cache *sample_struct_cachep;static void init_sample_struct_cache( void ){ sample_struct_cachep = kmem_cache_create( "sample_struct_cachep", /* Name */ sizeof(struct sample_struct), /* Object Size */ 0, /* Alignment */ SLAB_HWCACHE_ALIGN, /* Flags */ NULL); /* Constructor */ return;}接下来以专用slab缓存为实例
2. 使用所分配的 slab 缓存对象，或释放所分配的 slab 缓存对象
int slab_test( void ){ struct sample_struct *object; printk( "Cache name is %s/n", kmem_cache_name( sample_struct_cachep ) ); printk( "Cache object size is %d/n", kmem_cache_size( sample_struct_cachep ) ); object = kmem_cache_alloc(sample_struct_cachep, GFP_KERNEL); if (object) { kmem_cache_free(sample_struct_cachep, object); } return 0;}3. slab 缓存的销毁。调用者必须确保在执行销毁操作过程中，不要从缓存中分配对象。
static void remove_sample_struct_cache( void ){ if (sample_struct_cachep) kmem_cache_destroy( sample_struct_cachep ); return;}4.所在slab缓存使用过程中，可以通过slabtop查看。
5. 实例
/********************************************** * Author: lewiyon@hotmail.com * File name: slabmod.c * Description: slab缓存使用实例 * Date: 2012-07-26 *********************************************/#include <linux/init.h> #include <linux/module.h> #include <linux/module.h> #include <linux/unistd.h>//#include <sys/type.h>#include <linux/slab.h>MODULE_LICENSE("GPL"); #define first 1000 /* 第一次尝试分配1000个对象 */struct sample_struct { int id; char name[20]; char address[50];};static struct kmem_cache *sample_struct_cachep; static struct sample_struct *sample1[first];static int sample_mod_init(void){ int i; sample_struct_cachep = kmem_cache_create( "sample_struct_cachep", /* Name */ sizeof(struct sample_struct), /* Object Size */ 0, /* Alignment */ SLAB_HWCACHE_ALIGN, /* Flags */ NULL); /* Constructor */ /* 确保创建成功：有可能失败 */ if (NULL == sample_struct_cachep) return 1; printk(KERN_INFO "Cache name is %s\n", kmem_cache_name(sample_struct_cachep)); /* 首次分配 */ for (i = 0; i < first; i++) { sample1[i] = kmem_cache_alloc(sample_struct_cachep, GFP_KERNEL); if (NULL == sample1[i]) { int ii; printk("First alloc ERR: %d/n", i); for (ii = 0; ii < i; ii++) { kmem_cache_free(sample_struct_cachep, sample1[ii]); sample1[ii] = NULL; } } } return 0;}static void sample_mod_exit(void){ int i; if (sample1[0]) { for (i = 0; i < first; i++) { kmem_cache_free(sample_struct_cachep, sample1[i]); sample1[i] = NULL; } } if (sample_struct_cachep) { kmem_cache_destroy( sample_struct_cachep ); printk(KERN_INFO "Destroy sample_struct_cachep!\n"); } return ;} module_init(sample_mod_init); module_exit(sample_mod_exit);MODULE_AUTHOR("lewiyon@hotmail.com"); MODULE_DESCRIPTION("A Simple slab sample"); 插入模块、删除模块前后slabtop观察结果
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1020 100% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1010 99% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1002 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1001 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1000 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1000 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1000 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1000 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
1020 1000 98% 0.12K 34 30 136K sample_struct_cachep
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
[root@RedHat ~]# slabtop -o | egrep "OBJS|sample_struct_cachep"
OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
[root@RedHat ~]#
分析：
a. 再没有插入模块时，没有数据
b. 插入模块时，新建slab，这是数据都是active的，此时对象数目为OBJS = SLABS * OBJ/SLAB = 34*30 = 1020；
c. 随着模块稳定下来, 未使用的对象变为inactive，那么active数目就变味了1000；（与程序相对应）
d. 删除模块后，数据消失