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Migration will then fail in >> __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of >> such a race happening (leading to migration failure) by bailing out >> if we detect a PMD is marked with a migration entry. >> >> This fixes the migration-shared-anon-thp testcase failure on Apple M3. >> >> Note that, this is not a "fix" since it only reduces the chance of >> interference of khugepaged with migration, wherein both the kernel >> functionalities are deemed "best-effort". >> >> Signed-off-by: Dev Jain >> --- >> >> v1->v2: >>   - Remove SCAN_PMD_MIGRATION, merge into SCAN_PMD_MAPPED (David, >> Anshuman) >>   - Add a comment (Lorenzo) >> >> v1: >>   - https://lore.kernel.org/all/20250630044837.4675-1-dev.jain@arm.com/ >> >>   mm/khugepaged.c | 9 +++++++++ >>   1 file changed, 9 insertions(+) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 1aa7ca67c756..3fdefc4f4984 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -941,6 +941,15 @@ static inline int check_pmd_state(pmd_t *pmd) >>         if (pmd_none(pmde)) >>           return SCAN_PMD_NONE; >> + >> +    /* >> +     * The folio may be under migration when khugepaged is trying to >> +     * collapse it. Migration success or failure will eventually end >> +     * up with the PMD still pointing to a PMD-order folio, so return >> +     * SCAN_PMD_MAPPED. > > Nit: the last part (, so return ..) is obvious from the code. > > I would have written > > /* >  * The folio may be under migration when khugepaged is trying to >  * collapse it. Migration success or failure will eventually end >  * up with a present PMD entry again. >  */ > Thanks for the suggestion, but PMD pointing to PMD-order folio necessarily implies present PMD entry, but the converse is not true? For example it may point to a PTE table. So I wanted to make it explicitly clear that the transient entry will be converted to a PMD-THP in the end. > > Acked-by: David Hildenbrand Thanks!