请教：madvise为什么老是失败啊？（想调试下ksm）

learn007

1. #define        MEM_SIZE        (64*1024)
   
2. int main(int argc, char **argv)
   
3. {
   
4.         char *p = malloc(MEM_SIZE);
   
5.         int ps = getpagesize();
   
6. 
   
7.         printf("pagesize=%d\n", ps);
   
8.         if (!p)
   
9.         {
   
10.                 perror("oom");
    
11.                 return -1;
    
12.         }
    
13. 
    
14.         if (madvise(p, MEM_SIZE, MADV_MERGEABLE) != 0)
    
15.         {
    
16.                 perror("madvise");
    
17.                 return -1;
    
18.         }
    
19.        
    
20.         //advise_merge();
    
21.         memset(p, 0, 64*1024);
    
22.        
    
23.         while (1)
    
24.                 sleep(1);
    
25.         return 0;
    
26. }

复制代码

输出：
pagesize=4096
madvise: Invalid argument

openspace

       MADV_MERGEABLE (since Linux 2.6.32)
              Enable Kernel Samepage Merging (KSM) for the pages in the range specified by addr and length.  The kernel  regu‐
              larly scans those areas of user memory that have been marked as mergeable, looking for pages with identical con‐
              tent.  These are replaced by a single write-protected page (which is automatically copied  if  a  process  later
              wants  to update the content of the page).  KSM only merges private anonymous pages (see mmap(2)).  The KSM fea‐
              ture is intended for applications that generate many instances of the same data  (e.g.,  virtualization  systems
              such  as  KVM).  It can consume a lot of processing power; use with care.  See the kernel source file Documenta‐
              tion/vm/ksm.txt for more details.  The MADV_MERGEABLE and MADV_UNMERGEABLE operations are only available if  the
              kernel was configured with CONFIG_KSM.

可以看看内核有没有编译进KSM

embeddedlwp

回复 1# learn007


    addr is not page-aligned

learn007

回复 3# embeddedlwp


:wink: 后来发现需要用posix_memalign分配

embeddedlwp

回复 4# learn007


    yup