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Thu, 6 May 2021 12:15:31 +0000 Subject: Re: [PATCH v1 04/11] mm/memremap: add ZONE_DEVICE support for compound pages To: Matthew Wilcox References: <20210325230938.30752-1-joao.m.martins@oracle.com> <20210325230938.30752-5-joao.m.martins@oracle.com>

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no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; suspicious-header CC: "Aneesh Kumar K.V" , Linux MM , linux-nvdimm , Jason Gunthorpe , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton X-Mailman-Version: 3.1.1 Precedence: list List-Id: "Linux-nvdimm developer list." Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On 5/6/21 12:43 PM, Matthew Wilcox wrote: > On Thu, May 06, 2021 at 11:23:25AM +0100, Joao Martins wrote: >>>> I think it is ok for dax/nvdimm to continue to maintain their align >>>> value because it should be ok to have 4MB align if the device really >>>> wanted. However, when it goes to map that alignment with >>>> memremap_pages() it can pick a mode. For example, it's already the >>>> case that dax->align == 1GB is mapped with DEVMAP_PTE today, so >>>> they're already separate concepts that can stay separate. >>> >>> devdax namespace with align of 1G implies we expect to map them with 1G >>> pte entries? I didn't follow when you say we map them today with >>> DEVMAP_PTE entries. >> >> This sort of confusion is largelly why Dan is suggesting a @geometry for naming rather >> than @align (which traditionally refers to page tables entry sizes in pagemap-related stuff). >> >> DEVMAP_{PTE,PMD,PUD} refers to the representation of metadata in base pages (DEVMAP_PTE), >> compound pages of PMD order (DEVMAP_PMD) or compound pages of PUD order (DEVMAP_PUD). >> >> So, today: >> >> * namespaces with align of 1G would use *struct pages of order-0* (DEVMAP_PTE) backed with >> PMD entries in the direct map. >> * namespaces with align of 2M would use *struct pages of order-0* (DEVMAP_PTE) backed with >> PMD entries in the direct map. >> >> After this series: >> >> * namespaces with align of 1G would use *compound struct pages of order-30* (DEVMAP_PUD) >> backed with PMD entries in the direct map. > > order-18 > Right, thanks for the correction. Forgot to subtract PAGE_SIZE order (12). >> * namespaces with align of 1G would use *compound struct pages of order-21* (DEVMAP_PMD) >> backed with PTE entries in the direct map. > > i think you mean "align of 2M", and order-9. > True. > (note that these numbers are/can be different for powerpc since it > supports different TLB page sizes. please don't get locked into x86 > sizes, and don't ignore the benefits *to software* of managing memory > in sizes other than just those supported by the hardware). > I am not ignoring that either that I think. The page size looking values above is also what the consumer of this (device-dax) allows you to use as @align, hence why you see DEVMAP_PTE, PMD and PUD as the sizes. _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org