| Message ID | cover.1684397037.git.matsuda-daisuke@fujitsu.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | On-Demand Paging on SoftRoCE | expand |
Hello, On 5/18/23 16:21, Daisuke Matsuda wrote: > [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE > https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/ Quote from above link "There is a problem that data on DAX-enabled filesystem cannot be duplicated with software RAID or other hardware methods." Could you elaborate a bit more about the problem or any links about it? Thank you. Guoqing
On Fri, May 19, 2023 3:42 PM Guoqing Jiang wrote: > > Hello, > > On 5/18/23 16:21, Daisuke Matsuda wrote: > > [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE > > https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/ > > Quote from above link > > "There is a problem that data on DAX-enabled filesystem cannot be > duplicated with > software RAID or other hardware methods." > > Could you elaborate a bit more about the problem or any links about it? > Thank you. I am not an expert of Pmems, but my understanding is as follows: Pmem (Persistent memory) is detected as memory device during boot process. Physical addresses are allocated to them just like other memory in DIMM slots, so system have to treat them differently from traditional storage devices like HDD/SSD. It may be technically possible to duplicate data using multiple Pmems, but the duplication is practically not useful. For traditional storage devices, you can hot-remove and hot-add them easily on failure. However, Pmems are not attached to hot-pluggable slots. You have to halt the system and open the cabinet to change out the Pmem. This means availability of the system is not improved with data duplication on the same host. Daisuke > > Guoqing
On 5/19/23 17:57, Daisuke Matsuda (Fujitsu) wrote: > On Fri, May 19, 2023 3:42 PM Guoqing Jiang wrote: >> Hello, >> >> On 5/18/23 16:21, Daisuke Matsuda wrote: >>> [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE >>> https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/ >> Quote from above link >> >> "There is a problem that data on DAX-enabled filesystem cannot be >> duplicated with >> software RAID or other hardware methods." >> >> Could you elaborate a bit more about the problem or any links about it? >> Thank you. > I am not an expert of Pmems, but my understanding is as follows: > > Pmem (Persistent memory) is detected as memory device during boot process. > Physical addresses are allocated to them just like other memory in DIMM slots, > so system have to treat them differently from traditional storage devices like HDD/SSD. > > It may be technically possible to duplicate data using multiple Pmems, but the duplication > is practically not useful. For traditional storage devices, you can hot-remove and hot-add > them easily on failure. However, Pmems are not attached to hot-pluggable slots. You have > to halt the system and open the cabinet to change out the Pmem. This means availability > of the system is not improved with data duplication on the same host. I guess pmem with block translation table type would be fine since it can be used like normal storage device, but I am not pmem expert as well
This patch series implements the On-Demand Paging feature on SoftRoCE(rxe) driver, which has been available only in mlx5 driver[1] so far. There have been an obstacle to this series, but it has been finally solved. The commit 9b4b7c1f9f54 ("RDMA/rxe: Add workqueue support for rxe tasks") replaced the triple tasklets with a workqueue, and now it is ready to merge the ODP patches on top of it. I omitted some contents like the motive behind this series from the cover- letter. Please see the cover letter of v3 for more details[2]. [Overview] When applications register a memory region(MR), RDMA drivers normally pin pages in the MR so that physical addresses are never changed during RDMA communication. This requires the MR to fit in physical memory and inevitably leads to memory pressure. On the other hand, On-Demand Paging (ODP) allows applications to register MRs without pinning pages. They are paged-in when the driver requires and paged-out when the OS reclaims. As a result, it is possible to register a large MR that does not fit in physical memory without taking up so much physical memory. [How does ODP work?] "struct ib_umem_odp" is used to manage pages. It is created for each ODP-enabled MR on its registration. This struct holds a pair of arrays (dma_list/pfn_list) that serve as a driver page table. DMA addresses and PFNs are stored in the driver page table. They are updated on page-in and page-out, both of which use the common interfaces in the ib_uverbs layer. Page-in can occur when requester, responder or completer access an MR in order to process RDMA operations. If they find that the pages being accessed are not present on physical memory or requisite permissions are not set on the pages, they provoke page fault to make the pages present with proper permissions and at the same time update the driver page table. After confirming the presence of the pages, they execute memory access such as read, write or atomic operations. Page-out is triggered by page reclaim or filesystem events (e.g. metadata update of a file that is being used as an MR). When creating an ODP-enabled MR, the driver registers an MMU notifier callback. When the kernel issues a page invalidation notification, the callback is provoked to unmap DMA addresses and update the driver page table. After that, the kernel releases the pages. [Supported operations] All traditional operations are supported on RC connection. The new Atomic write[3] and RDMA Flush[4] operations are not included in this patchset. I will post them later after this patchset is merged. On UD connection, Send, Recv, and SRQ-Recv are supported. [How to test ODP?] There are only a few resources available for testing. pyverbs testcases in rdma-core and perftest[5] are recommendable ones. Other than them, the ibv_rc_pingpong command can also be used for testing. Note that you may have to build perftest from upstream because older versions do not handle ODP capabilities correctly. The ODP tree is available from github: https://github.com/daimatsuda/linux/tree/odp_v5 [Future work] My next work is to enable the new Atomic write[3] and RDMA Flush[4] operations with ODP. After that, I am going to implement the prefetch feature. It allows applications to trigger page fault using ibv_advise_mr(3) to optimize performance. Some existing software like librpma[6] use this feature. Additionally, I think we can also add the implicit ODP feature in the future. [1] [RFC 00/20] On demand paging https://www.spinics.net/lists/linux-rdma/msg18906.html [2] [PATCH for-next v3 0/7] On-Demand Paging on SoftRoCE https://lore.kernel.org/lkml/cover.1671772917.git.matsuda-daisuke@fujitsu.com/ [3] [PATCH v7 0/8] RDMA/rxe: Add atomic write operation https://lore.kernel.org/linux-rdma/1669905432-14-1-git-send-email-yangx.jy@fujitsu.com/ [4] [for-next PATCH 00/10] RDMA/rxe: Add RDMA FLUSH operation https://lore.kernel.org/lkml/20221206130201.30986-1-lizhijian@fujitsu.com/ [5] linux-rdma/perftest: Infiniband Verbs Performance Tests https://github.com/linux-rdma/perftest [6] librpma: Remote Persistent Memory Access Library https://github.com/pmem/rpma v4->v5: 1) Rebased to 6.4.0-rc2+ 2) Changed to schedule all works on responder and completer to workqueue v3->v4: 1) Re-designed functions that access MRs to use the MR xarray. 2) Rebased onto the latest jgg-for-next tree. v2->v3: 1) Removed a patch that changes the common ib_uverbs layer. 2) Re-implemented patches for conversion to workqueue. 3) Fixed compile errors (happened when CONFIG_INFINIBAND_ON_DEMAND_PAGING=n). 4) Fixed some functions that returned incorrect errors. 5) Temporarily disabled ODP for RDMA Flush and Atomic Write. v1->v2: 1) Fixed a crash issue reported by Haris Iqbal. 2) Tried to make lock patters clearer as pointed out by Romanovsky. 3) Minor clean ups and fixes. Daisuke Matsuda (7): RDMA/rxe: Always defer tasks on responder and completer to workqueue RDMA/rxe: Make MR functions accessible from other rxe source code RDMA/rxe: Move resp_states definition to rxe_verbs.h RDMA/rxe: Add page invalidation support RDMA/rxe: Allow registering MRs for On-Demand Paging RDMA/rxe: Add support for Send/Recv/Write/Read with ODP RDMA/rxe: Add support for the traditional Atomic operations with ODP drivers/infiniband/sw/rxe/Makefile | 2 + drivers/infiniband/sw/rxe/rxe.c | 18 ++ drivers/infiniband/sw/rxe/rxe.h | 37 --- drivers/infiniband/sw/rxe/rxe_comp.c | 12 +- drivers/infiniband/sw/rxe/rxe_hw_counters.c | 1 - drivers/infiniband/sw/rxe/rxe_hw_counters.h | 1 - drivers/infiniband/sw/rxe/rxe_loc.h | 45 +++ drivers/infiniband/sw/rxe/rxe_mr.c | 27 +- drivers/infiniband/sw/rxe/rxe_odp.c | 311 ++++++++++++++++++++ drivers/infiniband/sw/rxe/rxe_resp.c | 31 +- drivers/infiniband/sw/rxe/rxe_verbs.c | 5 +- drivers/infiniband/sw/rxe/rxe_verbs.h | 39 +++ 12 files changed, 447 insertions(+), 82 deletions(-) create mode 100644 drivers/infiniband/sw/rxe/rxe_odp.c base-commit: a7dae5daf4bf50de01ebdd192bf52c2e8cd80c75