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

posted on 2012-07-29 16:42  YoungerChina  阅读(838)  评论(0编辑  收藏  举报

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