Re: [PATCH v7 4/4] kexec_file: Load kernel at top of system RAM if required

On Wed, 18 Jul 2018 10:49:44 +0800 Baoquan He [off-list ref] wrote:

For kexec_file loading, if kexec_buf.top_down is 'true', the memory which
is used to load kernel/initrd/purgatory is supposed to be allocated from
top to down. This is what we have been doing all along in the old kexec
loading interface and the kexec loading is still default setting in some
distributions. However, the current kexec_file loading interface doesn't
do like this. The function arch_kexec_walk_mem() it calls ignores checking
kexec_buf.top_down, but calls walk_system_ram_res() directly to go through
all resources of System RAM from bottom to up, to try to find memory region
which can contain the specific kexec buffer, then call locate_mem_hole_callback()
to allocate memory in that found memory region from top to down. This brings
confusion especially when KASLR is widely supported , users have to make clear
why kexec/kdump kernel loading position is different between these two
interfaces in order to exclude unnecessary noises. Hence these two interfaces
need be unified on behaviour.

As far as I can tell, the above is the whole reason for the patchset,
yes?  To avoid confusing users.

Is that sufficient?  Can we instead simplify their lives by providing
better documentation or informative printks or better Kconfig text,
etc?

And who *are* the people who are performing this configuration?  Random
system administrators?  Linux distro engineers?  If the latter then
they presumably aren't easily confused!

In other words, I'm trying to understand how much benefit this patchset
will provide to our users as a whole.