On Jul 20, 2015, at 5:55 PM, Tom Talpey <tom@xxxxxxxxxx> wrote: > On 7/20/2015 1:55 PM, Chuck Lever wrote: >> On Jul 20, 2015, at 4:34 PM, Tom Talpey <tom@xxxxxxxxxx> wrote: >> >>> On 7/20/2015 12:03 PM, Chuck Lever wrote: >>>> All HCA providers have an ib_get_dma_mr() verb. Thus >>>> rpcrdma_ia_open() will either grab the device's local_dma_key if one >>>> is available, or it will call ib_get_dma_mr() which is a 100% >>>> guaranteed fallback. >>> >>> I recall that in the past, some providers did not support mapping >>> all of the machine's potential physical memory with a single dma_mr. >>> If an rnic did/does not support 44-ish bits of length per region, >>> for example. >> >> The buffers affected by this change are small, so I’m confident that >> restriction would not be a problem here. > > It's not about the buffer size, it's about the region. Because the > get_dma_mr does not specify a base address and length, the rnic must > basically attempt to map a base of zero and a length of the largest > physical offset. Understood now, but: > This is not the case with the previous phys_reg_mr, which specified > the exact phys page range. rpcrdma_ia_open() fails immediately if IB_DEVICE_LOCAL_DMA_LKEY is not asserted _and_ ib_get_dma_mr() fails. We never get to the logic in rpcrdma_regbuf_alloc() in that case, so ib_reg_phys_mr() would still never be invoked. That really is dead code. If you prefer, I can adjust the patch description to remove the “100% guaranteed fallback” line. -- Chuck Lever -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
