On Thu, Jun 18, 2020 at 01:47:20PM -0700, Heiner Litz wrote: > the striping explanation makes sense. In this case will rephase to: It > is sufficient to support large enough un-splittable writes to achieve > full per-zone bandwidth with a single writer/single QD. This is subject to the capabilities of the device and software's memory constraints. The maximum DMA size for a single request an nvme device can handle often range anywhere from 64k to 4MB. The pci nvme driver maxes out at 4MB anyway because that's the most we can guarantee forward progress right now, otherwise the scatter lists become to big to ensure we'll be able to allocate one to dispatch a write command. We do report the size and the alignment constraints so that it won't get split, but we still have to work with applications that don't abide by those constraints. > My main point is: There is no fundamental reason for splitting up > requests intermittently just to re-assemble them in the same form > later.
