On Wed, Sep 16, 2026 at 08:41:00AM +0200, David Hildenbrand (Arm) wrote: > On 9/15/26 11:21, Yeoreum Yun wrote: > > There are intermittent failures in collapse_max_ptes_swap() and > > collapse_max_ptes_shared() when using the khugepaged_context: > > > > # Run test: collapse_max_ptes_shared (khugepaged:anon) > > # Allocate huge page... OK > > # Share huge page over fork()... OK > > # Trigger CoW on page 1023 of 2048... OK > > # Maybe collapse with max_ptes_shared exceeded.... OK > > # Trigger CoW on page 1024 of 2048... Fail > > Bail out! Unexpected huge page > > # Planned tests != run tests (26 != 23) > > # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0 > > > > # Run test: collapse_max_ptes_swap (khugepaged:anon) > > # Swapout 257 of 2048 pages... OK > > # Maybe collapse with max_ptes_swap exceeded.... OK > > # Swapout 256 of 2048 pages... OK > > Bail out! Unexpected huge page > > # Planned tests != run tests (26 != 17) > > # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0 > > > > This happens because khugepaged may collapse the pages before > > wait_for_scan() > > is called, causing a sanity check that expects uncollapsed pages to fail. > > > > For example, in collapse_max_ptes_swap(), after faulting the pages back in > > and paging out up to max_ptes_swap pages, khugepaged may collapse them again > > before c->collapse() is called. > > > > To prevent this, change the khugepaged setting from ALWAYS to MADVICE for > > the affected tests, and mark the VMA with MADV_NOHUGEPAGE after it has been > > collapsed by wait_for_scan(). This prevents khugepaged from collapsing it > > again before c->collapse() is called. > > ALWAYS also respects MADV_NOHUGEPAGE, so why is the ALWAYS -> MADVICE > (MADVISE) > change required?
You're right. this is redundant and it's enough only set the VM_NOHUGEPAGE for anon. I'll remove them. Thanks! -- Sincerely, Yeoreum Yun
