On 01.09.25 14:54, David Hildenbrand wrote:
On 01.09.25 14:51, Wei Yang wrote:
On Mon, Sep 01, 2025 at 11:32:11AM +0200, David Hildenbrand wrote:
On 31.08.25 03:32, Zi Yan wrote:
On 29 Aug 2025, at 22:31, Wei Yang wrote:
The check of is_backed_by_folio() is done on each page.
Directly move pointer to next page instead of increase one and check if
it is page size aligned.
Signed-off-by: Wei Yang <[email protected]>
---
tools/testing/selftests/mm/split_huge_page_test.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
b/tools/testing/selftests/mm/split_huge_page_test.c
index 10ae65ea032f..7f7016ba4054 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -423,9 +423,8 @@ 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++)
- if (i % pagesize == 0 &&
- is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd,
kpageflags_fd))
+ for (i = 0; i < pagesize * 4; i += pagesize)
+ if (is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd,
kpageflags_fd))
thp_size++;
if (thp_size != 4)
It might be better to add
if (pte_mapped[i] != (char)i)
ksft_exit_fail_msg("%ld byte corrupted\n", i);
instead to make sure mremap() does not change pte_mapped[] values.
We do have a corruption check later in that function, so I think we can just
keep it simple here.
So this as is LGTM
Acked-by: David Hildenbrand <[email protected]>
As noted, we should just move from mremap() to mprotect() or sth like that
which has clearer semantics.
If my understanding is correct, we should
mmap 4 PMD_SIZE region with RW
madvise and fault in to allocate pmd-mapped thp
mprotect first page of each PMD to read-only to split to pte-mapped thp
check whether the page is backed by pmd-order folio
Is this the correct way?
Yeah, I would just mprotect(PROT_READ) the first page of each PMD. That
will trigger a PTE-mapping of the THP reliably.
Zi Yan mentions that there is a reason we are using mremap in the other
thread. So likely best to just keep it as is unless we can understand
that it definitely can done simpler.
--
Cheers
David / dhildenb
