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Date: Wed, 3 Sep 2014 23:21:03 +0300 From: Or Gerlitz <gerlitz.or@...il.com> To: Roland Dreier <roland@...nel.org> Cc: linux-rdma@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Sagi Grimberg <sagig@...lanox.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v1 for-next 00/16] On demand paging On Tue, Sep 2, 2014, Or Gerlitz <ogerlitz@...lanox.com> wrote: > On 7/3/2014 11:44 AM, Haggai Eran wrote: >> >> Hi Roland, >> >> I understand that you were reluctant to review these patches as long as >> there was an ongoing debate on whether or not the i_mmap_mutex should be >> changed into a spinlock. >> >> It seems that the debate concluded with the decision to change it into a >> rwsem [1], as apparently this provides the optimal performance with the new >> optimistic spinning patch [2]. >> >> I believe this means that there will be no problem adding paging support >> to the RDMA stack that depends on sleepable MMU notifiers. > > > Hi Roland, > > The ODP patch set was initially posted whole six months ago (March 2nd, > 2014). We did it prior to LSF so you can discuss that with Sagi while he's > there. Well no comment from your side so far. It's really (really) hard to > do proper kernel development when the sub-system maintainer doesn't provide > you almost no concrete feedback over half a year. > > Can you please go ahead and tell us your position re this features/patches? Hi Roland, Bump. Can you comment here? these patches were worked out here for long time by a dedicated group and implement a strategic feature for the RDMA industry. I don't see why the RDMA kernel maintainer can leave the development team in the air without any comment on their work for half a year. Or. >> Changes from V0: http://marc.info/?l=linux-rdma&m=139375790322547&w=2 >> >> - Rebased against latest upstream / for-next branch. >> - Removed dependency on patches that were accepted upstream. >> - Removed pre-patches that were accepted upstream [3]. >> - Add extended uverb call for querying device (patch 1) and use kernel >> device >> attributes to report ODP capabilities through the new uverb entry >> instead of >> having a special verb. >> - Allow upgrading page access permissions during page faults. >> - Minor fixes to issues that came up during regression testing of the >> patches. >> >> The following set of patches implements on-demand paging (ODP) support >> in the RDMA stack and in the mlx5_ib Infiniband driver. >> >> What is on-demand paging? >> >> Applications register memory with an RDMA adapter using system calls, >> and subsequently post IO operations that refer to the corresponding >> virtual addresses directly to HW. Until now, this was achieved by >> pinning the memory during the registration calls. The goal of on demand >> paging is to avoid pinning the pages of registered memory regions (MRs). >> This will allow users the same flexibility they get when swapping any >> other part of their processes address spaces. Instead of requiring the >> entire MR to fit in physical memory, we can allow the MR to be larger, >> and only fit the current working set in physical memory. >> >> This can make programming with RDMA much simpler. Today, developers that >> are working with more data than their RAM can hold need either to >> deregister and reregister memory regions throughout their process's >> life, or keep a single memory region and copy the data to it. On demand >> paging will allow these developers to register a single MR at the >> beginning of their process's life, and let the operating system manage >> which pages needs to be fetched at a given time. In the future, we might >> be able to provide a single memory access key for each process that >> would provide the entire process's address as one large memory region, >> and the developers wouldn't need to register memory regions at all. >> >> How does page faults generally work? >> >> With pinned memory regions, the driver would map the virtual addresses >> to bus addresses, and pass these addresses to the HCA to associate them >> with the new MR. With ODP, the driver is now allowed to mark some of the >> pages in the MR as not-present. When the HCA attempts to perform memory >> access for a communication operation, it notices the page is not >> present, and raises a page fault event to the driver. In addition, the >> HCA performs whatever operation is required by the transport protocol to >> suspend communication until the page fault is resolved. >> >> Upon receiving the page fault interrupt, the driver first needs to know >> on which virtual address the page fault occurred, and on what memory >> key. When handling send/receive operations, this information is inside >> the work queue. The driver reads the needed work queue elements, and >> parses them to gather the address and memory key. For other RDMA >> operations, the event generated by the HCA only contains the virtual >> address and rkey, as there are no work queue elements involved. >> >> Having the rkey, the driver can find the relevant memory region in its >> data structures, and calculate the actual pages needed to complete the >> operation. It then uses get_user_pages to retrieve the needed pages back >> to the memory, obtains dma mapping, and passes the addresses to the HCA. >> Finally, the driver notifies the HCA it can continue operation on the >> queue pair that encountered the page fault. The pages that >> get_user_pages returned are unpinned immediately by releasing their >> reference. >> >> How are invalidations handled? >> >> The patches add infrastructure to subscribe the RDMA stack as an mmu >> notifier client [4]. Each process that uses ODP register a notifier >> client. >> When receiving page invalidation notifications, they are passed to the >> mlx5_ib driver, which updates the HCA with new, not-present mappings. >> Only after flushing the HCA's page table caches the notifier returns, >> allowing the kernel to release the pages. >> >> What operations are supported? >> >> Currently only send, receive and RDMA write operations are supported on >> the >> RC protocol, and also send operations on the UD protocol. We hope to >> implement support for other transports and operations in the future. >> >> The structure of the patchset >> >> Patches 1-6: >> The first set of patches adds page fault support to the IB core layer, >> allowing MRs to be registered without their pages to be pinned. Patch 1 >> adds an extended verb to query device attributes, and patch 2 >> adds capability bits, configuration options, and a method for querying >> whether the paging capabilities from user-space. The next two patches >> (3-4) >> make some necessary changes to the ib_umem type. Patches 5 and 6 add >> paging support and invalidation support respectively. >> >> Patches 7-12: >> This set of patches add small size new functionality to the mlx5 driver >> and >> builds toward paging support. Patch 7 make changes to UMR mechanism >> (an internal mechanism used by mlx5 to update device page mappings). >> Patch 8 adds infrastructure support for page fault handling to the >> mlx5_core module. Patch 9 queries the device for paging capabilities, and >> patch 11 adds a function to do partial device page table updates. Finally, >> patch 12 adds a helper function to read information from user-space work >> queues in the driver's context. >> >> Patches 13-16: >> The final part of this patch set finally adds paging support to the mlx5 >> driver. Patch 13 adds in mlx5_ib the infrastructure to handle page faults >> coming from mlx5_core. Patch 14 adds the code to handle UD send page >> faults >> and RC send and receive page faults. Patch 15 adds support for page faults >> caused by RDMA write operations, and patch 16 adds invalidation support to >> the mlx5 driver, allowing pages to be unmapped dynamically. >> >> [1] [PATCH 0/5] mm: i_mmap_mutex to rwsem >> https://lkml.org/lkml/2013/6/24/683 >> >> [2] Re: Performance regression from switching lock to rw-sem for anon-vma >> tree >> https://lkml.org/lkml/2013/6/17/452 >> >> [3] pre-patches that were accepted upstream: >> a74d241 IB/mlx5: Refactor UMR to have its own context struct >> 48fea83 IB/mlx5: Set QP offsets and parameters for user QPs and not >> just for kernel QPs >> b475598 mlx5_core: Store MR attributes in mlx5_mr_core during creation >> and after UMR >> 8605933 IB/mlx5: Add MR to radix tree in reg_mr_callback >> >> [4] Integrating KVM with the Linux Memory Management (presentation), >> Andrea Archangeli >> >> http://www.linux-kvm.org/wiki/images/3/33/KvmForum2008%24kdf2008_15.pdf >> >> >> Haggai Eran (11): >> IB/core: Add an extended user verb to query device attributes >> IB/core: Replace ib_umem's offset field with a full address >> IB/core: Add umem function to read data from user-space >> IB/mlx5: Enhance UMR support to allow partial page table update >> net/mlx5_core: Add support for page faults events and low level >> handling >> IB/mlx5: Implement the ODP capability query verb >> IB/mlx5: Changes in memory region creation to support on-demand >> paging >> IB/mlx5: Add mlx5_ib_update_mtt to update page tables after creation >> IB/mlx5: Add function to read WQE from user-space >> IB/mlx5: Page faults handling infrastructure >> IB/mlx5: Handle page faults >> >> Sagi Grimberg (1): >> IB/core: Add flags for on demand paging support >> >> Shachar Raindel (4): >> IB/core: Add support for on demand paging regions >> IB/core: Implement support for MMU notifiers regarding on demand >> paging regions >> IB/mlx5: Add support for RDMA write responder page faults >> IB/mlx5: Implement on demand paging by adding support for MMU >> notifiers >> >> drivers/infiniband/Kconfig | 11 + >> drivers/infiniband/core/Makefile | 1 + >> drivers/infiniband/core/umem.c | 63 +- >> drivers/infiniband/core/umem_odp.c | 620 >> ++++++++++++++++++++ >> drivers/infiniband/core/umem_rbtree.c | 94 +++ >> drivers/infiniband/core/uverbs.h | 1 + >> drivers/infiniband/core/uverbs_cmd.c | 170 ++++-- >> drivers/infiniband/core/uverbs_main.c | 5 +- >> drivers/infiniband/hw/amso1100/c2_provider.c | 2 +- >> drivers/infiniband/hw/ehca/ehca_mrmw.c | 2 +- >> drivers/infiniband/hw/ipath/ipath_mr.c | 2 +- >> drivers/infiniband/hw/mlx5/Makefile | 1 + >> drivers/infiniband/hw/mlx5/main.c | 39 +- >> drivers/infiniband/hw/mlx5/mem.c | 67 ++- >> drivers/infiniband/hw/mlx5/mlx5_ib.h | 114 +++- >> drivers/infiniband/hw/mlx5/mr.c | 303 ++++++++-- >> drivers/infiniband/hw/mlx5/odp.c | 770 >> +++++++++++++++++++++++++ >> drivers/infiniband/hw/mlx5/qp.c | 198 +++++-- >> drivers/infiniband/hw/nes/nes_verbs.c | 4 +- >> drivers/infiniband/hw/ocrdma/ocrdma_verbs.c | 2 +- >> drivers/infiniband/hw/qib/qib_mr.c | 2 +- >> drivers/net/ethernet/mellanox/mlx5/core/eq.c | 11 +- >> drivers/net/ethernet/mellanox/mlx5/core/fw.c | 35 +- >> drivers/net/ethernet/mellanox/mlx5/core/main.c | 8 +- >> drivers/net/ethernet/mellanox/mlx5/core/qp.c | 134 ++++- >> include/linux/mlx5/device.h | 73 ++- >> include/linux/mlx5/driver.h | 20 +- >> include/linux/mlx5/qp.h | 63 ++ >> include/rdma/ib_umem.h | 29 +- >> include/rdma/ib_umem_odp.h | 156 +++++ >> include/rdma/ib_verbs.h | 47 +- >> include/uapi/rdma/ib_user_verbs.h | 25 + >> 32 files changed, 2907 insertions(+), 165 deletions(-) >> create mode 100644 drivers/infiniband/core/umem_odp.c >> create mode 100644 drivers/infiniband/core/umem_rbtree.c >> create mode 100644 drivers/infiniband/hw/mlx5/odp.c >> create mode 100644 include/rdma/ib_umem_odp.h >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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