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 Cy5OkE7I QCOzYRA4AHzPmM1fmaT2CP4Nm8wMMUuGVe+GXF/P/r6IIpsGnP3f5oTzUcVZz4hwYjZBK3Z0vtyUqhv/Bl6sZJ7iDFpBD16vU9nAFsxtizJe73klibRyMwZf3Uiqad4OIuevVmxzet/M/ZVi4SUD9Io6igkPWidmWVYfX4XwF6tAoKpmGw/Hab5t8MRbbYjL8EyPTzE139dT+wbEluGLk+T5TJuhVTfiDPkOhIWp084FXb9YzZDYx82EOaVUxOTZaGL9Igkda2sIl3yvYEx/ReFsEYNR3KQ3BaKLl2aoI/8UwoZewEK5STD9/S61EhV85jc0Toj8TykFuDko6OrZznneQa2xvprbByEdVjKLQUVzJpbHcTG5DISf9L0Pjlx4jQdRDlaXWIVBIXyjBRt0w0bJfKQ== 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: On 10/04/2023 22:39, Jane Chu wrote: > On 4/10/2023 10:47 AM, Joao Martins wrote: >> On 10/04/2023 18:27, Jane Chu wrote: >>> On 4/8/2023 3:19 AM, Aneesh Kumar K.V wrote: >>>> Jane Chu writes: >>>>> On 4/7/2023 5:23 AM, Aneesh Kumar K.V wrote: >>>>>> diff --git a/mm/Kconfig b/mm/Kconfig >>>>>> index ff7b209dec05..99f87c1be1e8 100644 >>>>>> --- a/mm/Kconfig >>>>>> +++ b/mm/Kconfig >>>>>> @@ -461,6 +461,9 @@ config SPARSEMEM_VMEMMAP >>>>>>           pfn_to_page and page_to_pfn operations.  This is the most >>>>>>           efficient option when sufficient kernel resources are available. >>>>>>     +config ARCH_WANT_OPTIMIZE_VMEMMAP >>>>>> +    bool >>>>>> + >>>>> >>>>> Could this devdax specific config switch be added to drivers/dax/Kconfig >>>>> ? also, how about adding 'DAX' to the config switch name? >>>> >>>> I would say we want to make it more generic. ie, both hugetlb and devdax >>>> can now derive the feature support via ARCH_WANT_OPTIMIZE_VMEMAP >>> >>> The two config switches have different purposes, it's better to keep them >>> separate.  For example, recent hugetlb high granularity mapping (HGM) project >>> requires to users to make a choice between HGM and hugetlb vmemmap >>> optimization(at least for now), while one can keep devdax compound page support >>> enabled. >>> >> >> Is it done by kconfig? If it helps: >> >> * there's a static key hugetlb can use to tell if this is enabled or not like >> how page_fixed_fake_head() uses it: >> >> if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key)) >>     ... >> >> * there's a hugetlb page bit for that vmemmap optimized pages with >> HpageOptimized(page). >> >> * there is a separate hugetlb CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP which is not >> the same as the ARCH kconfig. >> >> But perhaps there's some relevance in the ARCH_HUGETLB specific to HGMv2 that I >> am unaware. >> > > Looks like there is no consumer of CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP. > There are three ways to enable HVO via > CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON alone, or a combination of > CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP and boot param 'vmemmap_optimize_enabled' > or sysctl variable /proc/sys/vm/hugetlb_optimize_vmemmap. > > It seems that the devdax compound page support Let's call it devdax vmemmap deduplication as compound pages can work regardless of the trick. > does not cross path with HVO > which has a lot more moving arms, and so it's better to keep the devdax config > switch local to devdax and leave HVO alone. I agree; I would rather not change CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON nor CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP and its knobs. But to be clear the one I was talking about is ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP (which is selected by architecture) ... not the other ones. Which if it was a generic one would translate to 'can the architecture support deduplicated vmemmap' regardless of whether it is active or used by DAX/HVO. HVO would use its hugetlb kconfig knobs and function helpers pointed above to differentiate in the HVO-specific case as it does today. Perhaps we can hear also from Muchun on what he thinks is right for HVO. Joao