On Sun, May 12, 2019 at 02:55:48PM -0400, tedheadster wrote: > Christoph, > On the same hardware (reboot with different kernel) I am getting > _horrible_ disk I/O performance on the 5.1.1. kernel compiled on a > 32-bit platform using HIGHMEM64G (PAE) to access 32GiB of physical > memory. > > The numbers are truly terrible to copy a 16GiB file from one disk to a > different one: This sounds like your storage controller only supports 32-bit DMA. In that case any memory above that will be bounce buffered, that is copied from one piece of memory to another, which in addition to the copying will also create memory pressure. What storage controller do you use? Also if the CPU is 64-bit capable you really should use a 64-bit kernel with 32-bit userspace for a setup like that, as the VM folks do not spend any effort on optimizing large highmem setups.
