On Tue, Mar 24, 2020 at 08:09:19AM +0900, Tokunori Ikegami wrote: > Hi, > > The change looks okay, but why do we need such a large data length ? > > > > Do you have a use-case or performance numbers ? > > We use the large data length to get log page by the NVMe admin command. > In the past it was able to get with the same length but failed currently > with it. > > So it seems that depended on the kernel version as caused by the version up. We didn't have 32-bit max segments before, though. Why was 16-bits enough in older kernels? Which kernel did this stop working? > Also I have confirmed that currently failed with the length 0x10000000 > 256MB. If your hitting max segment limits before any other limit, you should be able to do larger transfers with more physically contiguous memory. Huge pages can get the same data length in fewer segments, if you want to try that. But wouldn't it be better if your application splits the transfer into smaller chunks across multiple commands? NVMe log page command supports offsets for this reason.
