關(guān)于slab的問(wèn)題

zhuqing_739

在網(wǎng)上找到了一段程序，是關(guān)于slab分配的，程序如下：

1. #include <linux/module.h>  
   
2. #include <linux/init.h>  
   
3. #include <linux/kernel.h>   
   
4. #include <linux/mm.h>  
   
5. #include <linux/errno.h>  
   
6. #include <linux/slab.h>  
   
7. #include <linux/gfp.h>  
   
8.   
   
9. struct slab_test{  
   
10.     int val;  
    
11. };  
    
12.   
    
13. static int n;  
    
14. struct kmem_cache *test_cachep = NULL;  
    
15. struct slab_test *object1 = NULL, *object2 = NULL;  
    
16.   
    
17. void slab_ctor(void *cachep){  
    
18.     printk("slab_ctor is called! object %d has been inited!\n", n);  
    
19.     n++;  
    
20. }  
    
21.   
    
22.   
    
23. static int __init slab_test_init(void){  
    
24.     printk("slab test module init\n");  
    
25.     n = 0;  
    
26.     test_cachep = kmem_cache_create("slab_test_cachep", sizeof(struct slab_test), 0, SLAB_HWCACHE_ALIGN, slab_ctor);  
    
27.     if(!test_cachep)  
    
28.         return -ENOMEM;  
    
29.     object1 = kmem_cache_alloc(test_cachep, GFP_KERNEL);  
    
30.     if(!object1)  
    
31.         return -ENOMEM;  
    
32.     else  
    
33.         printk("object one has been created!\n");  
    
34.     object2 = kmem_cache_alloc(test_cachep, GFP_KERNEL);  
    
35.     if(!object2)  
    
36.         return -ENOMEM;  
    
37.     else  
    
38.         printk("object two has been created!\n");  
    
39.     return 0;  
    
40. }  
    
41.   
    
42. static void __exit slab_test_exit(void){  
    
43.     printk("slab test module exit\n");  
    
44.     kmem_cache_free(test_cachep, object1);  
    
45.     kmem_cache_free(test_cachep, object2);  
    
46.     if(test_cachep)  
    
47.         kmem_cache_destroy(test_cachep);  
    
48. }  
    
49.   
    
50. module_init(slab_test_init);  
    
51. module_exit(slab_test_exit);  
    
52. MODULE_LICENSE("GPL");  
    
53. MODULE_AUTHOR("embeddedlwp@163.com");
    

復(fù)制代碼

我編譯后加載,出現(xiàn)這個(gè)打印信息：
slab test module init
slab_ctor is called! object 0 has been inited!
slab_ctor is called! object 1 has been inited!
......
......
slab_ctor is called! object 501 has been inited!
slab_ctor is called! object 502 has been inited!
slab_ctor is called! object 503 has been inited!
slab_ctor is called! object 504 has been inited!
slab_ctor is called! object 505 has been inited!
slab_ctor is called! object 506 has been inited!
slab_ctor is called! object 507 has been inited!
object one has been created!
object two has been created!
然后我cat /proc/slabinfo 得到：
/mnt/3515 $ cat /proc/slabinfo                        
slabinfo - version: 2.1
# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables <limit> <batchcount> <sharedfactor> : slabdata <active_slabs> <num_slabs> <sharedavail>
slab_test_cachep       2    508      4  508    1 : tunables  120   60    0 : slabdata      1      1      0
我想問(wèn)一下，這個(gè)508什么意思？怎么會(huì)出來(lái)個(gè)508？奇怪。。。。。謝謝

embeddedlwp

回復(fù) 1# zhuqing_739


我寫(xiě)的��？？貌似很明顯這個(gè)是object的數(shù)量啊，從0~507，是508個(gè)吧！


   

zhuqing_739

我的意思是怎么會(huì)爆出來(lái)個(gè) 508 ？？？？？？？？

zhuqing_739

{:3_190:}怎么不是其它的數(shù)呢？？？？？？？？？？

embeddedlwp

這個(gè)確實(shí)不知啊，等kouu兄指點(diǎn)！

kouu

slabinfo 里面有：objperslab==508、pagesperslab=1
說(shuō)明，slab里面object不足的時(shí)候最少分配一個(gè)page，而這個(gè)page分配之后會(huì)得到508個(gè)object。
至于為什么是508，這個(gè)就跟具體的機(jī)器情況、內(nèi)核版本、編譯選項(xiàng)、等有關(guān)了。大概猜測(cè)一下，機(jī)器應(yīng)該是32位的，object大小是sizeof(int)，4字節(jié)。由于帶有ctor，每個(gè)object要額外帶有一個(gè)sizeof(void*)作為空間鏈表中的next指針。那么一個(gè)object的大小就是8字節(jié)，508個(gè)object就是4064字節(jié)。還剩32字節(jié)，估計(jì)是保留空間，這個(gè)得根據(jù)具體內(nèi)核版本和編譯選項(xiàng)來(lái)解釋了……

embeddedlwp

回復(fù) 6# kouu

lz的kernel很有可能用的已經(jīng)是slub了，那么每個(gè)object的結(jié)構(gòu)如下



那么這個(gè)圖里的object align是多大呢？