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imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1719216028; a=rsa-sha256; cv=none; b=hf+6+uCgiez1tqwPDJmUuccCtD4fCLhCIx33RgF1z4BZAfMKGUW8TAu1+sjPP2aIekx69p SdYx4Chtg7Aq1Sn5jaV3wmVhd8n1juPx9c0K6wkV4WHHr/ptWyh275GGnMLuYhq7rUDJiI 9Ia811S0tsaaML5aNi+2qqhi/PuClwY= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E6825DA7; Mon, 24 Jun 2024 01:00:58 -0700 (PDT) Received: from [10.57.74.104] (unknown [10.57.74.104]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B92E73F6A8; Mon, 24 Jun 2024 01:00:31 -0700 (PDT) Message-ID: Date: Mon, 24 Jun 2024 09:00:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v2 0/9] Merge arm64/riscv hugetlbfs contpte support Content-Language: en-GB To: Alexandre Ghiti , 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: Ryan Roberts In-Reply-To: <863092ed-2b04-46bb-8d99-5796346cef3a@ghiti.fr> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 2CB351C000B X-Stat-Signature: 1ne9orbpmbw9fyj3bbtyk8jxynz6uf7b X-Rspam-User: X-HE-Tag: 1719216034-566016 X-HE-Meta: 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 lL1j+9vd f/rVS7z/bJMGRlDmuQgh2TjGR70RWMOVSyQXSvkDDjrU030N6MM7c3AgSVcmgDNGAYKFhScnJauSsE2h31X5Ht/Wfdzdno6TpbJUZX3m9Gy4Y6qjaipLrSnOxedxD6fm++NL2+KVRJXqKTcO93NsOpBz6oWnbKbqDpR4tQK3xHu1fnkXHnWvwMSojCyCtoEpCZvG282P44kBnZNFEIpLAK+f49x5tYcj9/x/367aSJkOmuoh4FBUoxivFHLlImAhy/ZhEVUtXg8sm7klBVcwtwLRFZL8Mtj4IIhMVvcYd6hZpRNbnJ1liTamIcFIR+wFg0R8UTIEs942dSaJejF4sXczJcqaptzzlovP5 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: 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? >>> >>> 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). > >> >>> 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! 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