Messages in this thread | | | Date | Thu, 7 Dec 2023 14:28:36 +0100 | Subject | Re: [PATCH v8 04/10] mm: thp: Support allocation of anonymous multi-size THP | From | David Hildenbrand <> |
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>> >> Right, but you know from the first loop which order is applicable (and will be >> fed to the second loop) and could just pte_unmap(pte) + tryalloc. If that fails, >> remap and try with the next orders. > > You mean something like this? > > pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK); > if (!pte) > return ERR_PTR(-EAGAIN); > > order = highest_order(orders); > while (orders) { > addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); > if (!pte_range_none(pte + pte_index(addr), 1 << order)) { > order = next_order(&orders, order); > continue; > } > > pte_unmap(pte); > > folio = vma_alloc_folio(gfp, order, vma, addr, true); > if (folio) { > clear_huge_page(&folio->page, vmf->address, 1 << order); > return folio; > } > > pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK); > if (!pte) > return ERR_PTR(-EAGAIN); > > order = next_order(&orders, order); > } > > pte_unmap(pte); > > I don't really like that because if high order folio allocations fail, then you > are calling pte_range_none() again for the next lower order; once that check has > succeeded for an order it shouldn't be required for any lower orders. In this > case you also have lots of pte map/unmap.
I see what you mean.
> > The original version feels more efficient to me. Yes it is. Adding in some comments might help, like
/* * Find the largest order where the aligned range is completely prot_none(). Note * that all remaining orders will be completely prot_none(). */ ...
/* Try allocating the largest of the remaining orders. */
> >> >> That would make the code certainly easier to understand. That "orders" magic of >> constructing, filtering, walking is confusing :) >> >> >> I might find some time today to see if there is an easy way to cleanup all what >> I spelled out above. It really is a mess. But likely that cleanup could be >> deferred (but you're touching it, so ... :) ). > > I'm going to ignore the last 5 words. I heard the "that cleanup could be > deferred" part loud and clear though :)
:)
If we could stop passing orders into thp_vma_allowable_orders(), that would probably be the biggest win. It's just all a confusing mess.
-- Cheers,
David / dhildenb
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