On 01.09.25 14:56, Zi Yan wrote:
On 1 Sep 2025, at 3:22, David Hildenbrand wrote:
On 31.08.25 04:27, Wei Yang wrote:
Subject: "selftests/mm: verify page content after remapping PMD through PTEs"
After mremap(), add a check on content to see whether mremap corrupt
data.
Signed-off-by: Wei Yang <richard.weiy...@gmail.com>
---
v2: add check on content instead of just test backed folio
I'm confused, don't we have that exact check later in the function?
Your v1 might have been better, unless I am missing something.
---
tools/testing/selftests/mm/split_huge_page_test.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
b/tools/testing/selftests/mm/split_huge_page_test.c
index 10ae65ea032f..229b6dcabece 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -423,10 +423,14 @@ static void split_pte_mapped_thp(void)
/* smap does not show THPs after mremap, use kpageflags instead */
thp_size = 0;
- for (i = 0; i < pagesize * 4; i++)
+ for (i = 0; i < pagesize * 4; i++) {
+ if (pte_mapped[i] != (char)i)
+ ksft_exit_fail_msg("%ld byte corrupted\n", i);
+
if (i % pagesize == 0 &&
is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd,
kpageflags_fd))
thp_size++;
+ }
if (thp_size != 4)
ksft_exit_fail_msg("Some THPs are missing during mremap\n");
I'm a bit confused with this test in general.
We do a
pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);
which I read as a "NOP".
Questions
(a) Will this actually do anything? Also, maybe it does now, but can't the
kernel just optimize that out in the future?
It remaps each subpage of 4 PMD THPs into a contiguous 2MB vaddr range and
perform split on that range.
I'm afraid I am missing the "why".
I would have thought that a "split_pte_mapped_thp" test would want to pte-map
THPs
to the see if they can be split.
Why is the mremap required? IOW, what exactly is the test trying to test that
exceeds "split_pte_mapped_thp" ?
--
Cheers
David / dhildenb
