linux-kernel - Re: [PATCH v2 5/6] userfaultfd: selftests: make /dev/userfaultfd testing configurable

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Date:   Tue, 26 Apr 2022 10:56:38 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Charan Teja Reddy <charante@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, zhangyi <yi.zhang@...wei.com>
Cc:     linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2 5/6] userfaultfd: selftests: make /dev/userfaultfd
 testing configurable

On 4/22/22 3:29 PM, Axel Rasmussen wrote:
> Instead of always testing both userfaultfd(2) and /dev/userfaultfd,
> let the user choose which to test.
> 
> As with other test features, change the behavior based on a new
> command line flag. Introduce the idea of "test mods", which are
> generic (not specific to a test type) modifications to the behavior of
> the test. This is sort of borrowed from this RFC patch series [1], but
> simplified a bit.
> 
> The benefit is, in "typical" configurations this test is somewhat slow
> (say, 30sec or something). Testing both clearly doubles it, so it may
> not always be desirable, as users are likely to use one or the other,
> but never both, in the "real world".
> 
> [1]: https://patchwork.kernel.org/project/linux-mm/patch/20201129004548.1619714-14-namit@vmware.com/
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> ---
>   tools/testing/selftests/vm/userfaultfd.c | 41 +++++++++++++++++-------
>   1 file changed, 30 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index 12ae742a9981..274522704e40 100644
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -142,8 +142,17 @@ static void usage(void)
>   {
>   	fprintf(stderr, "\nUsage: ./userfaultfd <test type> <MiB> <bounces> "
>   		"[hugetlbfs_file]\n\n");
> +

Remove the extra blank line here.

>   	fprintf(stderr, "Supported <test type>: anon, hugetlb, "
>   		"hugetlb_shared, shmem\n\n");
> +

Remove the extra blank line here.

> +	fprintf(stderr, "'Test mods' can be joined to the test type string with a ':'. "
> +		"Supported mods:\n");
> +	fprintf(stderr, "\tdev - Use /dev/userfaultfd instead of userfaultfd(2)\n");
> +	fprintf(stderr, "\nExample test mod usage:\n");
> +	fprintf(stderr, "# Run anonymous memory test with /dev/userfaultfd:\n");
> +	fprintf(stderr, "./userfaultfd anon:dev 100 99999\n\n");
> +
>   	fprintf(stderr, "Examples:\n\n");
>   	fprintf(stderr, "%s", examples);

Update examples above with new test cases if any.

>   	exit(1);
> @@ -1610,8 +1619,6 @@ unsigned long default_huge_page_size(void)
>   
>   static void set_test_type(const char *type)
>   {
> -	uint64_t features = UFFD_API_FEATURES;
> -
>   	if (!strcmp(type, "anon")) {
>   		test_type = TEST_ANON;
>   		uffd_test_ops = &anon_uffd_test_ops;
> @@ -1631,10 +1638,28 @@ static void set_test_type(const char *type)
>   		test_type = TEST_SHMEM;
>   		uffd_test_ops = &shmem_uffd_test_ops;
>   		test_uffdio_minor = true;
> -	} else {
> -		err("Unknown test type: %s", type);
> +	}

At this point, it might make it so much easier and maintainable if
we were to use getopt instead of parsing options.

> +}
> +
> +static void parse_test_type_arg(const char *raw_type)
> +{
> +	char *buf = strdup(raw_type);
> +	uint64_t features = UFFD_API_FEATURES;
> +
> +	while (buf) {
> +		const char *token = strsep(&buf, ":");
> +
> +		if (!test_type)
> +			set_test_type(token);
> +		else if (!strcmp(token, "dev"))
> +			test_dev_userfaultfd = true;
> +		else
> +			err("unrecognized test mod '%s'", token);
>   	}
>   
> +	if (!test_type)
> +		err("failed to parse test type argument: '%s'", raw_type);
> +
>   	if (test_type == TEST_HUGETLB)
>   		page_size = default_huge_page_size();
>   	else
> @@ -1681,7 +1706,7 @@ int main(int argc, char **argv)
>   		err("failed to arm SIGALRM");
>   	alarm(ALARM_INTERVAL_SECS);
>   
> -	set_test_type(argv[1]);
> +	parse_test_type_arg(argv[1]);
>   
>   	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
>   	nr_pages_per_cpu = atol(argv[2]) * 1024*1024 / page_size /
> @@ -1719,12 +1744,6 @@ int main(int argc, char **argv)
>   	}
>   	printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
>   	       nr_pages, nr_pages_per_cpu);
> -
> -	test_dev_userfaultfd = false;
> -	if (userfaultfd_stress())
> -		return 1;
> -
> -	test_dev_userfaultfd = true;
>   	return userfaultfd_stress();
>   }
>   
> 

Same comments as before on fail vs. skip conditions to watch out
for and report them correctly.

thanks,
-- Shuah