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Message-ID: <63b9dc1c-7bf6-4de7-8d23-cf54e3408207@arm.com> Date: Fri, 1 Mar 2024 11:38:05 +0000 From: Ryan Roberts <ryan.roberts@....com> To: Alexandre Ghiti <alexghiti@...osinc.com> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Andrew Morton <akpm@...ux-foundation.org>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, linux-mm@...ck.org Subject: Re: [PATCH 0/9] Merge arm64/riscv hugetlbfs contpte support On 01/03/2024 11:29, Alexandre Ghiti wrote: > Hi Ryan, > > On Fri, Mar 1, 2024 at 11:45 AM Ryan Roberts <ryan.roberts@....com> wrote: >> >> Hi Alexandre, >> >> I confess I haven't looked at the patches yet, but this cover letter raises a >> few quesions for me. I'll aim to look at the actual patches in due course. >> >> On 01/03/2024 09:14, 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. >> >> Yes that makes sense to me. The intention for mTHP (!hugetlb) is to fully >> encapsulate PTEs beind set_ptes(), ptep_get() and friends, so what's actually >> written to the pgtable is arch-specific and well abstracted. >> >>> >>> 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. >> >> You seem to be talking about both hugetlb (which uses the "huge" pte helpers) >> and contpte for THP (i.e. mTHP, which uses the regular pte helpers). They are >> pretty separate in my mind, so not sure why you would be modifying them both in >> the same series? > > I don't, this patchset only deals with hugetlb, I just meant that this > series was just the beginning as I'm working on moving the contpte for > THP support in the generic code for riscv to use. Ahh got it! Thanks for the explanation. > > Sorry my wording was ambiguous :) > > Thanks, > > Alex > >> >> Thanks, >> Ryan >> >>> >>> 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@arm.com/ >>> >>> 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 | 59 +++++- >>> 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 | 120 +++++++++++- >>> arch/riscv/mm/hugetlbpage.c | 227 ---------------------- >>> mm/Kconfig | 3 + >>> mm/Makefile | 1 + >>> mm/contpte.c | 268 +++++++++++++++++++++++++ >>> 11 files changed, 456 insertions(+), 528 deletions(-) >>> create mode 100644 mm/contpte.c >>> >>
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