On Wed, Sep 02, 2026 at 01:09:35PM +0100, Yeoreum Yun wrote: > There're some random failure for split_huge_page_test when khugepaged > collapses pages into pmd again which had split by the test. > > Prevent the khugepaged's collapses for split page by setting the > mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
Maybe worth saying that MADV_NOHUGEPAGE doesn't immediately split anything, just prevents future khugepaged collapses? > > Suggested-by: Kevin Brodsky <[email protected]> > Suggested-by: Lorenzo Stoakes (ARM) <[email protected]> > Signed-off-by: Yeoreum Yun <[email protected]> LGTM, thanks, with a few nits above/below (sorry! :P) Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]> > --- > tools/testing/selftests/mm/split_huge_page_test.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c > b/tools/testing/selftests/mm/split_huge_page_test.c > index 86a603692826..4bbad892bc57 100644 > --- a/tools/testing/selftests/mm/split_huge_page_test.c > +++ b/tools/testing/selftests/mm/split_huge_page_test.c > @@ -168,6 +168,14 @@ static char *allocate_zero_filled_hugepage(size_t len) > return result; > } > > +static void madv_nohuge(void *addr, size_t len) Maybe call it disable_khugepaged() to make it explicit that's what this is doing rather than eliminating any THP pages in the range? > +{ Maybe a comment here like: /* * Disables khugepaged from collapsing THPs in range, existing THP * pages remain. */ > + if (!madvise(addr, len, MADV_NOHUGEPAGE)) > + return; > + > + ksft_exit_fail_msg("MADV_NOHUGEPAGE failed, err=%d\n", errno); > +} > + > static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int > nr_hpages, size_t len) > { > unsigned long rss_anon_before, rss_anon_after; > @@ -180,6 +188,9 @@ static void > verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp > if (!rss_anon_before) > ksft_exit_fail_msg("No RssAnon is allocated before split\n"); > > + /* Prevent khugepaged from collapsing the pages. */ > + madv_nohuge(one_page, len); > + > /* split all THPs */ > write_debugfs(PID_FMT, getpid(), (uint64_t)one_page, > (uint64_t)one_page + len, 0); > @@ -227,6 +238,9 @@ static void split_pmd_thp_to_order(int order) > if (!check_huge_anon(one_page, 4 * pmd_pagesize, 4, pmd_pagesize)) > ksft_exit_fail_msg("No THP is allocated\n"); > > + /* Prevent khugepaged from collapsing the pages. */ > + madv_nohuge(one_page, len); > + > /* split all THPs */ > write_debugfs(PID_FMT, getpid(), (uint64_t)one_page, > (uint64_t)one_page + len, order); > @@ -275,6 +289,9 @@ static void split_pte_mapped_thp(void) > goto out; > } > > + /* Prevent khugepaged from collapsing the pages. */ > + madv_nohuge(thp_area, thp_area_size); > + > /* > * To challenge spitting code, we will mremap a single page of each > * THP (page[i] of thp[i]) in the thp_area into page_area. This will > @@ -542,6 +559,8 @@ static int create_pagecache_thp_and_fd(const char > *testfile, size_t fd_size, > ksft_test_result_skip("Pagecache folio split skipped\n"); > return -2; > } > + /* Prevent khugepaged from collapsing the pages. */ > + madv_nohuge(*addr, fd_size); > return 0; > err_out_close: > close(*fd); > > -- > 2.43.0 > -- Cheers, Lorenzo
