Hi Ryan, On Fri, May 10, 2024 at 3:49 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > On 08/05/2024 12:34, Alexandre Ghiti wrote: > > This patchset intends to merge the contiguous ptes hugetlbfs implementation > > of arm64 and riscv. > > > > Both arm64 and riscv support the use of contiguous ptes to map pages that > > are larger than the default page table size, respectively called contpte > > and svnapot. > > > > The riscv implementation differs from the arm64's in that the LSBs of the > > pfn of a svnapot pte are used to store the size of the mapping, allowing > > for future sizes to be added (for now only 64KB is supported). That's an > > issue for the core mm code which expects to find the *real* pfn a pte points > > to. Patch 1 fixes that by always returning svnapot ptes with the real pfn > > and restores the size of the mapping when it is written to a page table. > > > > The following patches are just merges of the 2 different implementations > > that currently exist in arm64 and riscv which are very similar. It paves > > the way to the reuse of the recent contpte THP work by Ryan [1] to avoid > > reimplementing the same in riscv. > > Hi Alexandre, > > I've skimmed through this series and the one that moves contpte. I can see there > is definitely value in sharing the implementation, and the rough shape of things > seems appropriate. I had some minor concerns about making it harder to implement > potential future arm64 errata workarounds but on reflection, most of the > now-shared code is really just wrapping the primitives that are still arch-specific. > > I'm going to need to spend proper time reviewing it to give detailed feedback, > but I'll be out on paternity leave for 3 weeks from end of Monday at the latest. Too bad, I expected to discuss that with you at LSF/MM...But congrats! Hope your wife is fine :) > So realistically I won't be able to do the detailed review until at least the > first week of June. > > Some high level thoughts: > > - huge_ptep_* functions could be working on different sized huge ptes - arm64 > supports contpte, pmd, contpmd and pud. Is keeping them in contpte.c > appropriate? Hmm indeed, I'll see what I can do. > Perhaps it's better to keep huge_pte and contpte separate? Also, it > only works on arm64 because we can get away with calling the lower-level pte > functions even when the huge_pte is actually a contpmd/pmd/pud, because the > format is the same. That might present challenges to other arches if the format > is different? Yes, but I think that if that happens, we could get away with it by choosing the right function depending on the size of the mapping? > > - It might be easier to review if the arm64 stuff is first moved (without > changes) then modified to make it suitable for riscv, then for riscv to be > hooked up. At the moment I'm trying to follow all 3 parts per-function. Ok, let me give it a try during your paternity leave! > > Thanks, > Ryan Thanks, Alex > > > > > > This patchset was tested by running the libhugetlbfs testsuite with 64KB > > and 2MB pages on both architectures (on a 4KB base page size arm64 kernel). > > > > [1] https://lore.kernel.org/linux-arm-kernel/20240215103205.2607016-1-ryan.roberts@xxxxxxx/ > > > > Changes in v2: > > - Rebase on top of 6.9-rc3 > > > > Alexandre Ghiti (9): > > riscv: Restore the pfn in a NAPOT pte when manipulated by core mm code > > riscv: Safely remove huge_pte_offset() when manipulating NAPOT ptes > > mm: Use common huge_ptep_get() function for riscv/arm64 > > mm: Use common set_huge_pte_at() function for riscv/arm64 > > mm: Use common huge_pte_clear() function for riscv/arm64 > > mm: Use common huge_ptep_get_and_clear() function for riscv/arm64 > > mm: Use common huge_ptep_set_access_flags() function for riscv/arm64 > > mm: Use common huge_ptep_set_wrprotect() function for riscv/arm64 > > mm: Use common huge_ptep_clear_flush() function for riscv/arm64 > > > > arch/arm64/Kconfig | 1 + > > arch/arm64/include/asm/pgtable.h | 56 +++++- > > arch/arm64/mm/hugetlbpage.c | 291 +--------------------------- > > arch/riscv/Kconfig | 1 + > > arch/riscv/include/asm/hugetlb.h | 2 +- > > arch/riscv/include/asm/pgtable-64.h | 11 ++ > > arch/riscv/include/asm/pgtable.h | 153 +++++++++++++-- > > arch/riscv/mm/hugetlbpage.c | 227 ---------------------- > > arch/riscv/mm/pgtable.c | 6 +- > > mm/Kconfig | 3 + > > mm/Makefile | 1 + > > mm/contpte.c | 272 ++++++++++++++++++++++++++ > > 12 files changed, 480 insertions(+), 544 deletions(-) > > create mode 100644 mm/contpte.c > > >
