Messages in this thread | | | Subject | RDMA memory registration (was: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation) | From | Roland Dreier <> | Date | Fri, 29 Apr 2005 09:45:50 -0700 |
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Is there anything wrong with the following plan?
1) For memory registration, use get_user_pages() in the kernel. Use locked_vm and RLIMIT_MEMLOCK to limit the amount of memory pinned by a given process. One disadvantage of this is that the accounting will overestimate the amount of pinned memory if a process pins the same page twice, but this doesn't seem that bad to me -- it errs on the side of safety.
2) For fork() support:
a) Extend mprotect() with PROT_DONTCOPY so processes can avoid copy-on-write problems.
b) (maybe someday?) Add a VM_ALWAYSCOPY flag and extend mprotect() with PROT_ALWAYSCOPY so processes can mark pages to be pre-copied into child processes, to handle the case where only half a page is registered.
I believe this puts the code that must be trusted into the kernel and gives userspace primitives that let apps handle the rest.
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