On Thu, Sep 10, 2026 at 07:14:42PM +0800, Baolin Wang wrote: > > > On 9/10/26 6:45 PM, Kiryl Shutsemau wrote: > > 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 The changelog is out of date, sorry: since 6dedaf0d46a9 check_huge_anon() 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. > > OK. But can we extend the check_huge_xxx() functions to meet your > requirements, for example by adding a check_aligned_huge_xxx() that wraps > the underlying implementation of check_large_folios()? > > I still find it confusing that khugepaged.c has two separate sets of > functions for checking large folios.
Agreed that two sets is one too many. Yeoreum's series rewrites check_huge_xxx() on top of pagemap and kpageflags, which is what is_backed_by_folio() already walks, so once that lands the two can meet: the mTHP branch of check_huge() checks each window for a folio of the order at its start, and is_range_backed_by_order() goes away or becomes its internal. That also makes the generic mTHP cases stricter for free. I would rather do that as a follow-up than fold it into either series now, since both touch the same functions. -- Kiryl Shutsemau / Kirill A. Shutemov
