Messages in this thread | | | Date | Mon, 31 Jan 2022 11:56:36 -0700 | Subject | Re: [PATCH v5 00/24] Userspace P2PDMA with O_DIRECT NVMe devices | From | Jonathan Derrick <> |
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Hi Logan,
On 1/27/2022 5:25 PM, Logan Gunthorpe wrote: > Hi, > > This patchset continues my work to add userspace P2PDMA access using > O_DIRECT NVMe devices. This posting fixes a lot of issues that were > addresed in the last posting, which is here[1]. > > The patchset is rebased onto v5.17-rc1 as well as a rebased version of > Ralph Campbell's patches to drop the ZONE_DEVICE page ref count offset. > My understanding is this patch has some problems that are yet to be > resolved but this will be the direction taken going forward and is > included here to show that it is compatible with this patchset. > > The patchset enables userspace P2PDMA by allowing userspace to mmap() > allocated chunks of the CMB. The resulting VMA can be passed only > to O_DIRECT IO on NVMe backed files or block devices. A flag is added > to GUP() in Patch 16, then Patches 17 through 21 wire this flag up based > on whether the block queue indicates P2PDMA support. Patches 22 > through 24 enable the CMB to be mapped into userspace by mmaping > the nvme char device. > > This is relatively straightforward, however the one significant > problem is that, presently, pci_p2pdma_map_sg() requires a homogeneous > SGL with all P2PDMA pages or all regular pages. Enhancing GUP to > support enforcing this rule would require a huge hack that I don't > expect would be all that pallatable. So patches 3 to 16 add > support for P2PDMA pages to dma_map_sg[table]() to the dma-direct > and dma-iommu implementations. Thus systems without an IOMMU plus > Intel and AMD IOMMUs are supported. (Other IOMMU implementations would > then be unsupported, notably ARM and PowerPC but support would be added > when they convert to dma-iommu). Am I understanding that an IO may use a mix of p2pdma and system pages? Would that cause inconsistent latencies?
> > dma_map_sgtable() is preferred when dealing with P2PDMA memory as it > will return -EREMOTEIO when the DMA device cannot map specific P2PDMA > pages based on the existing rules in calc_map_type_and_dist(). > > The other issue is dma_unmap_sg() needs a flag to determine whether a > given dma_addr_t was mapped regularly or as a PCI bus address. To allow > this, a third flag is added to the page_link field in struct > scatterlist. This effectively means support for P2PDMA will now depend > on CONFIG_64BIT. > > Feedback welcome. > > This series is based on v5.17-rc1. A git branch is available here: > > https://github.com/sbates130272/linux-p2pmem/ p2pdma_user_cmb_v5 > > Thanks, > > Logan > > [1] https://lore.kernel.org/all/20211117215410.3695-1-logang@deltatee.com/T/#u > > -- > > Changes since v4: > - Rebase onto v5.17-rc1. > - Included Ralph Cambell's patches which removes the ZONE_DEVICE page > reference count offset. This is just to demonstrate that this > series is compatible with that direction. > - Added a comment in pci_p2pdma_map_sg_attrs(), per Chaitanya and > included his Reviewed-by tags. > - Patch 1 in the last series which cleaned up scatterlist.h > has been upstreamed. > - Dropped NEED_SG_DMA_BUS_ADDR_FLAG seeing depends on doesn't > work with selected symbols, per Christoph. > - Switched iov_iter_get_pages_[alloc_]flags to be exported with > EXPORT_SYMBOL_GPL, per Christoph. > - Renamed zone_device_pages_are_mergeable() to > zone_device_pages_have_same_pgmap(), per Christoph. > - Renamed .mmap_file_open operation in nvme_ctrl_ops to > cdev_file_open(), per Christoph. > > Changes since v3: > - Add some comment and commit message cleanups I had missed for v3, > also moved the prototypes for some of the p2pdma helpers to > dma-map-ops.h (which I missed in v3 and was suggested in v2). > - Add separate cleanup patch for scatterlist.h and change the macros > to functions. (Suggested by Chaitanya and Jason, respectively) > - Rename sg_dma_mark_pci_p2pdma() and sg_is_dma_pci_p2pdma() to > sg_dma_mark_bus_address() and sg_is_dma_bus_address() which > is a more generic name (As requested by Jason) > - Fixes to some comments and commit messages as suggested by Bjorn > and Jason. > - Ensure swiotlb is not used with P2PDMA pages. (Per Jason) > - The sgtable coversion in RDMA was split out and sent upstream > separately, the new patch is only the removal. (Per Jason) > - Moved the FOLL_PCI_P2PDMA check outside of get_dev_pagemap() as > Jason suggested this will be removed in the near term. > - Add two patches to ensure that zone device pages with different > pgmaps are never merged in the block layer or > sg_alloc_append_table_from_pages() (Per Jason) > - Ensure synchronize_rcu() or call_rcu() is used before returning > pages to the genalloc. (Jason pointed out that pages are not > gauranteed to be unused in all architectures until at least > after an RCU grace period, and that synchronize_rcu() was likely > too slow to use in the vma close operation. > - Collected Acks and Reviews by Bjorn, Jason and Max. > > Logan Gunthorpe (22): > lib/scatterlist: add flag for indicating P2PDMA segments in an SGL > PCI/P2PDMA: Attempt to set map_type if it has not been set > PCI/P2PDMA: Expose pci_p2pdma_map_type() > PCI/P2PDMA: Introduce helpers for dma_map_sg implementations > dma-mapping: allow EREMOTEIO return code for P2PDMA transfers > dma-direct: support PCI P2PDMA pages in dma-direct map_sg > dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support > iommu/dma: support PCI P2PDMA pages in dma-iommu map_sg > nvme-pci: check DMA ops when indicating support for PCI P2PDMA > nvme-pci: convert to using dma_map_sgtable() > RDMA/core: introduce ib_dma_pci_p2p_dma_supported() > RDMA/rw: drop pci_p2pdma_[un]map_sg() > PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg() > mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages > iov_iter: introduce iov_iter_get_pages_[alloc_]flags() > block: add check when merging zone device pages > lib/scatterlist: add check when merging zone device pages > block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages() > block: set FOLL_PCI_P2PDMA in bio_map_user_iov() > mm: use custom page_free for P2PDMA pages > PCI/P2PDMA: Introduce pci_mmap_p2pmem() > nvme-pci: allow mmaping the CMB in userspace > > Ralph Campbell (2): > ext4/xfs: add page refcount helper > mm: remove extra ZONE_DEVICE struct page refcount > > arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- > block/bio.c | 10 +- > block/blk-map.c | 7 +- > drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- > drivers/infiniband/core/rw.c | 45 +-- > drivers/iommu/dma-iommu.c | 67 +++- > drivers/nvme/host/core.c | 18 +- > drivers/nvme/host/nvme.h | 4 +- > drivers/nvme/host/pci.c | 97 +++--- > drivers/nvme/target/rdma.c | 2 +- > drivers/pci/Kconfig | 5 + > drivers/pci/p2pdma.c | 441 +++++++++++++++++++++---- > fs/dax.c | 8 +- > fs/ext4/inode.c | 5 +- > fs/fuse/dax.c | 4 +- > fs/xfs/xfs_file.c | 4 +- > include/linux/dax.h | 10 + > include/linux/dma-map-ops.h | 76 +++++ > include/linux/dma-mapping.h | 5 + > include/linux/memremap.h | 7 +- > include/linux/mm.h | 68 ++-- > include/linux/pci-p2pdma.h | 38 +-- > include/linux/scatterlist.h | 44 ++- > include/linux/uio.h | 6 + > include/rdma/ib_verbs.h | 11 + > include/uapi/linux/magic.h | 1 + > kernel/dma/direct.c | 43 ++- > kernel/dma/direct.h | 7 +- > kernel/dma/mapping.c | 22 +- > lib/iov_iter.c | 25 +- > lib/scatterlist.c | 25 +- > lib/test_hmm.c | 2 +- > mm/gup.c | 22 +- > mm/internal.h | 8 + > mm/memcontrol.c | 6 +- > mm/memremap.c | 75 ++--- > mm/migrate.c | 5 - > mm/page_alloc.c | 3 + > mm/swap.c | 45 +-- > 39 files changed, 904 insertions(+), 371 deletions(-) > > > base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07 > -- > 2.30.2
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