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I'm developing a system that uses RDMA extensively (on Mellanox hardware) and would like to be able to register memory regions more efficiently/faster.

I have taken a look into Fast Memory Registration and I have a few questions:

  1. Is FMR going away? From here [1] it seems it might get removed/replaced soon.

  2. Is there any user-space code out there that makes use of this feature? There are only a few threads online discussing this and mostly in the context of kernel modules.

Any useful pointers would be greatly appreciated.

[1] https://jira.hpdd.intel.com/browse/LU-5783

JC1
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It seems that kernel developers would like to get FMR removed. See for example this future of FMR thread on linux-rdma.

FMR (and FRWR) are only used in the kernel. User-space isn't trusted to use these operations as they allow access to the physical address space and could break process isolation.

haggai_e
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  • Yes, but FMR memory can be registered from user-space [1]. If you know of any public code that uses this feature I would like to take a look. [1] http://lxr.free-electrons.com/source/include/rdma/ib_verbs.h?v=3.2#L734 – JC1 Oct 18 '16 at 20:46
  • This is fast registration, not FMR. Take a look at http://lxr.free-electrons.com/source/drivers/infiniband/core/uverbs_cmd.c?v=4.8#L2493, it is not possible to post a fast registration work request from userspace. – haggai_e Oct 18 '16 at 21:00
  • Thanks for the clarification. I was not aware of that. – JC1 Oct 20 '16 at 05:47
  • Yes , FMR is removed.and all kernel code containing that.https://lore.kernel.org/linux-rdma/12-v3-f58e6669d5d3+2cf-fmr_removal_jgg@mellanox.com/ – Alok Prasad Jul 01 '20 at 12:22