[PATCH 2/2] mm/selftests: Don't prefault in gup_longterm tests
From: Peter Xu <peterx@redhat.com>
Date: 2024-04-28 19:01:59
Also in:
linux-mm, lkml
Subsystem:
kernel selftest framework, memory management - gup (get user pages), memory management - misc, the rest · Maintainers:
Shuah Khan, Andrew Morton, David Hildenbrand, Linus Torvalds
Prefault, especially with RW, makes the GUP test too easy, and may not yet reach the core of the test. For example, R/O longterm pins will just hit, pte_write()==true for whatever cases, the unsharing logic won't be ever tested. This patch remove the prefault. This tortures more code paths at least to cover the unshare care for R/O longterm pins, in which case the first R/O GUP attempt will fault in the page R/O first, then the 2nd will go through the unshare path, checking whether an unshare is needed. Cc: David Hildenbrand <redacted> Signed-off-by: Peter Xu <peterx@redhat.com> --- tools/testing/selftests/mm/gup_longterm.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/gup_longterm.c b/tools/testing/selftests/mm/gup_longterm.c
index ad168d35b23b..488e32186246 100644
--- a/tools/testing/selftests/mm/gup_longterm.c
+++ b/tools/testing/selftests/mm/gup_longterm.c@@ -119,10 +119,16 @@ static void do_test(int fd, size_t size, enum test_type type, bool shared) } /* - * Fault in the page writable such that GUP-fast can eventually pin - * it immediately. + * Explicitly avoid pre-faulting in the page, this can help testing + * more code paths. + * + * Take example of an upcoming R/O pin test, if we RW prefault the + * page, such pin will directly skip R/O unsharing and the longterm + * pin will success mostly always. When not prefaulted, R/O + * longterm pin will first fault in a RO page, then the 2nd round + * it'll go via the unshare check. Otherwise those paths aren't + * covered. */ - memset(mem, 0, size); switch (type) { case TEST_TYPE_RO:
--
2.44.0