On Wed, Sep 09, 2026 at 06:01:13PM +0800, Baolin Wang wrote: > > > On 9/8/26 8:50 PM, Kiryl Shutsemau wrote: > > From: "Kiryl Shutsemau (Meta)" <[email protected]> > > > > An mTHP collapse test needs to know that a range is backed by folios of the > > target order, and that they sit where a collapse would put them. Nothing > > answers that today: is_backed_by_folio() classifies the folio behind a > > single page, and check_huge_anon() reads smaps AnonHugePages, which only > > accounts PMD mappings. > > Have you checked check_large_folios() in vm_util.c? It seems to meet your > requirements, or am I missing something?
The changelog is out of date, sorry: since 6dedaf0d46a9 check_huge_anon() counts mTHP folios through check_large_folios() rather than reading smaps, and it is what check_huge() already uses for mthp_khugepaged. It could do this job too, called once per window. What is_range_backed_by_order() adds is alignment check: the folio has to sit at the window start. And check_large_folios() reopens two fds per per call which kinda wasteful. The collapse_order_* cases check three windows per case, so I wanted a helper whose contract is "this window is one folio of this order". I will fix the changelog if the series gets respun. -- Kiryl Shutsemau / Kirill A. Shutemov
