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imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of alex@ghiti.fr designates 217.70.183.195 as permitted sender) smtp.mailfrom=alex@ghiti.fr; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1719906682; a=rsa-sha256; cv=none; b=WKP1akko7f5y9J7c6/xqyt2v7RNZHtL2bc+0OyhNjSDXNX+hbUnE1m8Wh3BsDppJC49qVy 0rj1Kww1IcdoObOaF0Rtiy37IlEFEQpBT1q3lNNb1mnlnVlo756dq/A8wQfORJoec25X+g oMRXKMJf7FItj0wxQevtWPFxFa0kA5Y= Received: by mail.gandi.net (Postfix) with ESMTPSA id 4669860007; Tue, 2 Jul 2024 07:51:27 +0000 (UTC) Message-ID: Date: Tue, 2 Jul 2024 09:51:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v2 0/9] Merge arm64/riscv hugetlbfs contpte support Content-Language: en-US To: Ryan Roberts , Alexandre Ghiti Cc: Catalin Marinas , Will Deacon , Mark Rutland , Paul Walmsley , Palmer Dabbelt , Albert Ou , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org References: <20240508113419.18620-1-alexghiti@rivosinc.com> <6d37f914-d139-48ea-be63-c428ac767cc1@arm.com> <863092ed-2b04-46bb-8d99-5796346cef3a@ghiti.fr> From: Alexandre Ghiti In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-GND-Sasl: alex@ghiti.fr X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 37B8AA0005 X-Stat-Signature: o3zp49p75uica1nh1bu3b575fiu8cjbd X-HE-Tag: 1719906692-262710 X-HE-Meta: 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 HxNUkicV Z5Ys79vTTqQse9fgoOI9vnHnvMw5ExL4Y7ykbHGtHtkrtxfwWc8pugwSO6542Tt5w7W3zztOBOPZ1UnZ9f9YnjJovFcbLYvO2+5s2BKRz4KEtM9L51W0/NOi++QZXzSquuFNu6Kp7ByiPMLNu0pBf/QW1KRD6Z96yhqRxP/0cyNeQABSVp/ZKdnwKUBGT8fBoM1VGS9sJRYMu5Yp9PkZ74R+r3P5OPy/eeRvxurK7mCixbf7E5hZTIHGd8G0tnRLgyIFnhAmZaLBi3Tg8Nz3SBPHXqsgPckKMrmHj X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Ryan, On 24/06/2024 10:00, Ryan Roberts wrote: > On 28/05/2024 09:07, Alexandre Ghiti wrote: >> Hi Ryan, >> >> On 12/05/2024 19:25, Alexandre Ghiti wrote: >>> Hi Ryan, >>> >>> On Fri, May 10, 2024 at 3:49 PM Ryan Roberts 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. > Hi Alexandre, > > Sorry for the radio silence. I'm back at work now and have some cycles to review > this. Did you ever post a new version based on the suggestions below? Unfortunately no, other things happened that took all my attention, sorry. >>>> 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. >> >> So I took a look at that. It amounts to doing the same as what we do for THP >> contptes, ie having both contpte-aware and "normal" APIs. Let's take for example >> huge_ptep_get(), below is what I get. To me it's not that bad, so I'll implement >> this unless there is strong opposition. > I'm not sure I've understood what you are going here... see below. > >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index f8efbc128446..869a9aae6c68 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -1715,6 +1715,16 @@ static inline void clear_young_dirty_ptes(struct >> vm_area_struct *vma, >>                 contpte_clear_young_dirty_ptes(vma, addr, ptep, nr, flags); >>  } >> >> +static inline pte_t huge_ptep_get(pte_t *ptep) >> +{ >> +        pte_t orig_pte = __ptep_get(ptep); >> + >> +        if (!pte_present(orig_pte) || !pte_cont(orig_pte)) >> +                return orig_pte; >> + >> +        return contpte_huge_ptep_get(ptep); > A "huge pte" is not the same as a "cont pte". A huge pte is an abstract thing, > which maybe of a number of different sizes; on arm64 with 4K base pages, 64K, > 2M, 32M, 1G are supported. The 64K size is implemented using the PTE_CONT bit at > PTE level. 2M is a single PMD level block, 32M uses PMD_CONT at PMD level and 1G > is 1 PUD block. So I'm not sure it makes sense to tie this up with "contpte_" > functions? > >> +} >> + >>  #else /* CONFIG_ARM64_CONTPTE */ >> >>  #define ptep_get                               __ptep_get >> @@ -1736,6 +1746,8 @@ static inline void clear_young_dirty_ptes(struct >> vm_area_struct *vma, >>  #define ptep_set_access_flags __ptep_set_access_flags >>  #define clear_young_dirty_ptes __clear_young_dirty_ptes >> >> +#define huge_ptep_get                          __ptep_get > I don't quite understand the logic here. huge ptes are needed for hugetlb so > their definition needs to be tied to that, not to ARM64_CONTPTE, which is an > independent feature. > >> + >>  #endif /* CONFIG_ARM64_CONTPTE */ >> >>  #endif /* !__ASSEMBLY__ */ >> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c >> index 3f09ac73cce3..aa0ee3f02226 100644 >> --- a/arch/arm64/mm/hugetlbpage.c >> +++ b/arch/arm64/mm/hugetlbpage.c >> @@ -127,28 +127,6 @@ static inline int num_contig_ptes(unsigned long size, >> size_t *pgsize) >>         return contig_ptes; >>  } >> >> -pte_t huge_ptep_get(pte_t *ptep) >> -{ >> -       int ncontig, i; >> -       size_t pgsize; >> -       pte_t orig_pte = __ptep_get(ptep); >> - >> -       if (!pte_present(orig_pte) || !pte_cont(orig_pte)) >> -               return orig_pte; >> - >> -       ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize); >> -       for (i = 0; i < ncontig; i++, ptep++) { >> -               pte_t pte = __ptep_get(ptep); >> - >> -               if (pte_dirty(pte)) >> -                       orig_pte = pte_mkdirty(orig_pte); >> - >> -               if (pte_young(pte)) >> -                       orig_pte = pte_mkyoung(orig_pte); >> -       } >> -       return orig_pte; >> -} >> - >>  /* >>   * Changing some bits of contiguous entries requires us to follow a >>   * Break-Before-Make approach, breaking the whole contiguous set >> diff --git a/mm/contpte.c b/mm/contpte.c >> new file mode 100644 >> index 000000000000..4e742cf00b6f >> --- /dev/null >> +++ b/mm/contpte.c >> @@ -0,0 +1,17 @@ >> +pte_t contpte_huge_ptep_get(pte_t *ptep) >> +{ >> +        int ncontig, i; >> +        size_t pgsize; >> + >> +        ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize); >> +        for (i = 0; i < ncontig; i++, ptep++) { >> +                pte_t pte = __ptep_get(ptep); >> + >> +                if (pte_dirty(pte)) >> +                        orig_pte = pte_mkdirty(orig_pte); >> + >> +                if (pte_young(pte)) >> +                        orig_pte = pte_mkyoung(orig_pte); >> +        } >> +        return orig_pte; >> +} > I guess your observation is that contpte_ and hugepte_ code looks similar so it > shold be grouped? I think if we can get some actual reuse that might make sense, > but as implemented, this function is completely separate from > contpte_ptep_get(). I wonder if its simpler just to have contpte.c for contpte_ > and hugepte_.c for hugepte_ then they can be included in the build independently > based on arch/core Kconfigs (e.g. CONFIG_HUGETLB_PAGE vs CONFIG_ARM64_CONTPTE). Yes, you're right, this was just rambling :) > >>>> 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! > Review would certainly be easier with this approach! I'll do my best to do that soon. Hope everything went well for you. Thanks, Alex > > Thanks, > Ryan > >>>> 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@arm.com/ >>>>> >>>>> 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 >>>>> >>> _______________________________________________ >>> linux-riscv mailing list >>> linux-riscv@lists.infradead.org >>> http://lists.infradead.org/mailman/listinfo/linux-riscv