Re: [LTP] [PATCH] mem/tunable: new testcase about max_map_count tunable

[Caspar Zhang <caspar@casparzhang.com>]

On 02/13/2012 02:18 PM, Zhouping Liu wrote:
> 
> The program is designed to test max_map_count tunable file
> 
> The kernel Documentation say that:
> /proc/sys/vm/max_map_count contains the maximum number of memory map
> areas a process may have. Memory map areas are used as a side-effect
> of calling malloc, directly by mmap and mprotect, and also when
> loading shared libraries.
> 
> Each process has his own maps file: /proc/[pid]/maps, and each line
> indicates a map entry, so it can caculate the amount of maps by reading
> the file lines' number to check the tunable performance.
> 
> The program trys to invoke mmap() endless until triggering MAP_FAILED,
> then read the process's maps file /proc/[pid]/maps, save the line number
> to map_count variable, and compare it with /proc/sys/vm/max_map_count,
> map_count should less than max_map_count.
> Note: There are two special vmas VDSO and VSYSCALL, which are allocated
> via install_special_mapping(), install_specail_mapping() allows the VMAs
> to be allocated and inserted without checking the sysctl_map_map_count,
> and each /proc/<pid>/maps has both at the end:
> ...
> ...
> 7fff7b9ff000-7fff7ba00000 r-xp 00000000 00:00 0           [vdso]
> ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0   [vsyscall]
> 
> so during comparing with map_count and /proc/sys/vm/max_map_count,
> we should except the two special vmas from map_count:
> map_count -= 2;
> 
> While most applications need less than a thousand maps, and the tunable
> default value is 65530.
> When the value is too large or too little, the system would hang, so I
> choose four special value to test, which can coverage most situation:
> a) Default value / 100
> b) Default value / 10
> c) Default value
> d) Default value * 10
> 
> Signed-off-by: Zhouping Liu <zliu@redhat.com>
> ---
>  runtest/mm                                   |    2 +
>  testcases/kernel/mem/tunable/max_map_count.c |  197 ++++++++++++++++++++++++++
>  2 files changed, 199 insertions(+), 0 deletions(-)
>  create mode 100644 testcases/kernel/mem/tunable/max_map_count.c
> 

Acked-by: Caspar Zhang <caspar@casparzhang.com>


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