Re: [PATCH v6 3/3] selftests/mm: add new selftests for KSM

[David Hildenbrand <david@redhat.com>]

On 12.04.23 05:16, Stefan Roesch wrote:
> This adds three new tests to the selftests for KSM.  These tests use the
> new prctl API's to enable and disable KSM.
> 
> 1) add new prctl flags to prctl header file in tools dir
> 
>     This adds the new prctl flags to the include file prct.h in the
>     tools directory.  This makes sure they are available for testing.
> 
> 2) add KSM prctl merge test
> 
>     This adds the -t option to the ksm_tests program.  The -t flag
>     allows to specify if it should use madvise or prctl ksm merging.
> 
> 3) add KSM get merge type test
> 
>     This adds the -G flag to the ksm_tests program to query the KSM
>     status with prctl after KSM has been enabled with prctl.
> 
> 4) add KSM fork test
> 
>     Add fork test to verify that the MMF_VM_MERGE_ANY flag is inherited
>     by the child process.
> 
> 5) add two functions for debugging merge outcome
> 
>     This adds two functions to report the metrics in /proc/self/ksm_stat
>     and /sys/kernel/debug/mm/ksm.
> 
> The debugging can be enabled with the following command line:
> make -C tools/testing/selftests TARGETS="mm" --keep-going \
>          EXTRA_CFLAGS=-DDEBUG=1

Would it make sense to instead have a "-D" (if still unused) runtime 
options to print this data? Dead code that's not compiled is a bit 
unfortunate as it can easily bit-rot.



This patch essentially does two things

1) Add the option to run all tests/benchmarks with the PRCTL instead of 
MADVISE

2) Add some functional KSM tests for the new PRCTL (fork, enabling 
works, disabling works).

The latter should rather go into ksm_functional_tests().

[...]

>   
> -static int check_ksm_unmerge(int mapping, int prot, int timeout, size_t page_size)
> +/* Verify that prctl ksm flag is inherited. */
> +static int check_ksm_fork(void)
> +{
> +	int rc = KSFT_FAIL;
> +	pid_t child_pid;
> +
> +	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
> +		perror("prctl");
> +		return KSFT_FAIL;
> +	}
> +
> +	child_pid = fork();
> +	if (child_pid == 0) {
> +		int is_on = prctl(PR_GET_MEMORY_MERGE, 0);
> +
> +		if (!is_on)
> +			exit(KSFT_FAIL);
> +
> +		exit(KSFT_PASS);
> +	}
> +
> +	if (child_pid < 0)
> +		goto out;
> +
> +	if (waitpid(child_pid, &rc, 0) < 0)
> +		rc = KSFT_FAIL;
> +
> +	if (prctl(PR_SET_MEMORY_MERGE, 0)) {
> +		perror("prctl");
> +		rc = KSFT_FAIL;
> +	}
> +
> +out:
> +	if (rc == KSFT_PASS)
> +		printf("OK\n");
> +	else
> +		printf("Not OK\n");
> +
> +	return rc;
> +}
> +
> +static int check_ksm_get_merge_type(void)
> +{
> +	if (prctl(PR_SET_MEMORY_MERGE, 1)) {
> +		perror("prctl set");
> +		return 1;
> +	}
> +
> +	int is_on = prctl(PR_GET_MEMORY_MERGE, 0);
> +
> +	if (prctl(PR_SET_MEMORY_MERGE, 0)) {
> +		perror("prctl set");
> +		return 1;
> +	}
> +
> +	int is_off = prctl(PR_GET_MEMORY_MERGE, 0);
> +
> +	if (is_on && is_off) {
> +		printf("OK\n");
> +		return KSFT_PASS;
> +	}
> +
> +	printf("Not OK\n");
> +	return KSFT_FAIL;
> +}

Yes, these two are better located in ksm_functional_tests() to just run 
them both automatically when the test is executed.

-- 
Thanks,

David / dhildenb