On Wed, Dec 4, 2024 at 8:43 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Wed, Dec 4, 2024, at 14:29, Brian Gerst wrote: > > On Wed, Dec 4, 2024 at 5:34 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: > >> > >> - In the early days of x86-64 hardware, there was sometimes the need > >> to run a 32-bit kernel to work around bugs in the hardware drivers, > >> or in the syscall emulation for 32-bit userspace. This likely still > >> works but there should never be a need for this any more. > >> > >> Removing this also drops the need for PHYS_ADDR_T_64BIT and SWIOTLB. > >> PAE mode is still required to get access to the 'NX' bit on Atom > >> 'Pentium M' and 'Core Duo' CPUs. > > > > 8GB of memory is still useful for 32-bit guest VMs. > > Can you give some more background on this? > > It's clear that one can run a virtual machine this way and it > currently works, but are you able to construct a case where this > is a good idea, compared to running the same userspace with a > 64-bit kernel? > > From what I can tell, any practical workload that requires > 8GB of total RAM will likely run into either the lowmem > limits or into virtual addressig limits, in addition to the > problems of 32-bit kernels being generally worse than 64-bit > ones in terms of performance, features and testing. I use a 32-bit VM to test 32-bit kernel builds. I haven't benchmarked kernel builds with 4GB/8GB yet, but logically more memory would be better for caching files. Brian Gerst
