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From:   Axel Rasmussen <axelrasmussen@google.com>
Date:   Thu, 19 May 2022 12:13:18 -0700
Message-ID: <CAJHvVcj8FnOAQ7HqrgiXiN+k2=XbXPerLZy6QBG1mDMW3=7ewA@mail.gmail.com>
Subject: Re: [PATCH v2 5/6] userfaultfd: selftests: make /dev/userfaultfd
 testing configurable
To:     Shuah Khan <skhan@linuxfoundation.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Charan Teja Reddy <charante@codeaurora.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
        Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
        Jonathan Corbet <corbet@lwn.net>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Peter Xu <peterx@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        zhangyi <yi.zhang@huawei.com>, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Linuxkselftest <linux-kselftest@vger.kernel.org>
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On Tue, Apr 26, 2022 at 9:56 AM Shuah Khan <skhan@linuxfoundation.org> wrote:
>
> 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@google.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.

Will fix the above comments in v3.

>
> >       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.

Agreed, I'd like that as well. But, since it's a bigger refactor that
affects all test types, I think it may be cleaner to leave it for a
follow-up series.

>
> > +}
> > +
> > +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.

I think in v3 things will be correct. Basically, in the skip cases we
just exit(KSFT_SKIP) directly, instead of relying on the return value
here. I'll take a pass and double check though before sending v3.

>
> thanks,
> -- Shuah
>