Re: [LTP] [PATCH v6 2/2] mem/tunable: new testcase about overcommiting memory

Re: [LTP] [PATCH v6 2/2] mem/tunable: new testcase about overcommiting memory

[Caspar Zhang]

On 11/15/2011 09:19 PM, Zhouping Liu wrote:
> hi, Cyril & Garrett
> 
> please feel free to comment the patch.
> 
> There are two tunables overcommit_memory and overcommit_ratio under
> /proc/sys/vm/, which can control memory overcommitment.
> 
> The overcommit_memory contains a flag that enables memory
> overcommitment, it has three values:
> - When this flag is 0, the kernel attempts to estimate the amount
>   of free memory left when userspace requests more memory.
> - When this flag is 1, the kernel pretends there is always enough
>   memory until it actually runs out.
> - When this flag is 2, the kernel uses a "never overcommit" policy
>   that attempts to prevent any overcommit of memory.
> 
> The overcommit_ratio tunable defines the amount by which the kernel
> overextends its memory resources in the event that overcommit_memory
> is set to the value of 2. The value in this file represents a
> percentage added to the amount of actual RAM in a system when
> considering whether to grant a particular memory request.
> The general formula for this tunable is:
> CommitLimit = SwapTotal + MemTotal * overcommit_ratio
> CommitLimit, SwapTotal and MemTotal can read from /proc/meminfo.
> 
> The program is designed to test the two tunables:
> 
> When overcommit_memory = 0, allocatable memory can't overextends
> the amount of free memory. I choose the three cases:
> a. less than free_total:    free_total / 2, alloc should pass.
> b. equal to free_total:     free_total,     alloc should pass.
> c. greater than free_total: free_total * 2, alloc should fail.
> 
> When overcommit_memory = 1, it can alloc enough much memory,
> I choose the three cases:
> a. less than sum_total:    sum_total / 2, alloc should pass.
> b. equal to sum_total:     sum_total,     alloc should pass.
> c. greater than sum_total: sum_total * 2, alloc should pass.
> *note: sum_total = SwapTotal + MemTotal
> 
> When overcommit_memory = 2,
> allocatable memory = CommitLimit - Committed_As
> I define it as commit_left, also I choose three cases:
> a. less than commit_left:    commit_left / 2, alloc should pass.
> b. greater than commit_left: commit_left * 2, alloc should fail.
> c. overcommit limit:         CommitLimit,     alloc should fail.
> *note: CommitLimit is the current overcommit limit.
>       Committed_AS is the amount of memory that system has used.
> why I din't choose 'equal to commit_left' as a case, because in
> this case, the result is not fixed after I tested some times.
> 
> References:
> - Documentation/sysctl/vm.txt
> - Documentation/vm/overcommit-accounting
> 
> Signed-off-by: Zhouping Liu <zliu@redhat.com>

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

> ---
>  testcases/kernel/mem/tunable/Makefile            |   42 ++++
>  testcases/kernel/mem/tunable/overcommit_memory.c |  278 ++++++++++++++++++++++
>  2 files changed, 320 insertions(+), 0 deletions(-)
>  create mode 100644 testcases/kernel/mem/tunable/Makefile
>  create mode 100644 testcases/kernel/mem/tunable/overcommit_memory.c

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