> On Jul 10, 2017, at 10:26 AM, Sagi Grimberg <sagi@xxxxxxxxxxx> wrote: > > >> I thought the FMR page list limit was always 64. I seem to >> vaguely recall testing this way back when I split out the >> xprtrdma code for handling different registration modes, >> and above 64, FMR fell over (at least with CX2 and CX3). > > Not sure about CX2, but iser runs fmrs with 128 entries perfectly fine > on CX3. IIRC CX2 does not support FRWRs, CX2 does indeed support both FMR and FRWR. > CX4 and up does not support FMRs (which I'd love to kill altogether > anyways). "Killing in-kernel FMR" might be a good topic for the LPC RDMA micro-conference. > The motivation is to not guess empirically what is the max page_list > for FMRs which is supposed to be on its way out anyhow. 1. I concur that it would be good to have some API for advertising the limit for FMR. If it's higher than 64 for some devices, that will be good for performance. 2. But I'm not sure it's always the same as the device's FRWR maximum page list depth. If it is always or often smaller, then that unfairly limits FRWR. 3. I'm not at all objecting, but if FMR is to go away, why make this change now? -- Chuck Lever -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
