Re: [LTP] [PATCH] Set tunable value of min_free_kbytes lower

[Shuang Qiu <shuang.qiu@oracle.com>]

On 08/27/2012 01:16 PM, Zhouping Liu wrote:
>
> ----- Original Message -----
> For the issue that min_free_kbytes caused system hang, I prepared a patch for it,
> at the same time, in order to enlarge the case's coverage, I add a new case(2x default_tune)
> I have tested it in my box, it's good.
>
> Shuang, can you review and test the patch?
>
> diff --git a/testcases/kernel/mem/tunable/min_free_kbytes.c b/testcases/kernel/mem/tunable/min_free_kbytes.c
> index 00ead04..ded0e45 100644
> --- a/testcases/kernel/mem/tunable/min_free_kbytes.c
> +++ b/testcases/kernel/mem/tunable/min_free_kbytes.c
> @@ -10,7 +10,8 @@
>    * the current free memory with the tunable value repeatedly.
>    *
>    * a) default min_free_kbytes with all overcommit memory policy
> - * b) half of mem_free with all overcommit memory policy
> + * b) 2x default value with all overcommit memory policy
> + * c) 10% of MemFree or %5 MemTotal with all overcommit memory policy
>    *
>    ********************************************************************
>    * Copyright (C) 2012 Red Hat, Inc.
> @@ -115,20 +116,27 @@ int main(int argc, char *argv[])
>   static void test_tune(unsigned long overcommit_policy)
>   {
>          int status;
> -       int pid[2];
> +       int pid[3];
>          int ret, i;
> -       unsigned long tune, memfree;
> +       unsigned long tune, memfree, memtotal;
>   
>          set_sys_tune("overcommit_memory", overcommit_policy, 1);
>   
> -       for (i = 0; i < 2; i++) {
> +       for (i = 0; i < 3; i++) {
>                  /* case1 */
>                  if (i == 0)
>                          set_sys_tune("min_free_kbytes", default_tune, 1);
>                  /* case2 */
> -               else {
> +               else if (i == 1) {
> +                       set_sys_tune("min_free_kbytes", 2 * default_tune, 1);
> +               /* case3 */
> +               } else {
>                          memfree = read_meminfo("MemFree:");
> -                       tune = memfree / 2;
> +                       memtotal = read_meminfo("MemTotal:");
> +                       tune = memfree / 10;
> +                       if (tune > (memtotal / 20))
> +                               tune = memtotal / 20;
> +
>                          set_sys_tune("min_free_kbytes", tune, 1);
>                  }
>   
Hi Zhouping,
I have tested this patch,it works.

But I found another problem with this case that it is not work 
expectedly with the scenario that i386 system(PAE kernel) which has >4GB 
memory.
i.e. In i386 system with 7GB free memory,it could only eat about 3GB 
memory in one mem-hog fork process.

And we can also patch the overflow issue which I mentioned before:

The type of total_mem "unsigned long" is not suitable with nowadays
memory ,it will overflow(with i386) in line 177:map_count = total_mem
*
KB / MAP_SIZE and the value of map_count is not correct.
Using "unsigned long long" could fix this issue.

Thanks
Shuang

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