[PATCH v5 11/16] kexec: add config option for KHO

[Dave Young]

On Wed, 26 Mar 2025 at 19:34, Mike Rapoport <rppt at kernel.org> wrote:
>
> Hi Dave,
>
> On Wed, Mar 26, 2025 at 05:17:16PM +0800, Dave Young wrote:
> > On Tue, 25 Mar 2025 at 16:36, Dave Young <dyoung at redhat.com> wrote:
> > >
> > > > >
> > > > > Have you tested kdump?  In my mind there are two issues,  one is with
> > > > > CMA enabled, it could cause kdump crashkernel memory reservation
> > > > > failures more often due to the fragmented low memory.  Secondly,  in
> > > >
> > > > kho scracth memorys are reserved much later than crashkernel, we may not
> > > > need to worry about it.
> > > > ====================
> > > > start_kernel()
> > > >   ......
> > > >   -->setup_arch(&command_line);
> > > >      -->arch_reserve_crashkernel();
> > > >   ......
> > > >   -->mm_core_init();
> > > >      -->kho_memory_init();
> > > >
> > > > > kdump kernel dump the crazy scratch memory in vmcore is not very
> > > > > meaningful.  Otherwise I suspect this is not tested under kdump.  If
> > > > > so please disable this option for kdump.
> > >
> > > Ok,  it is fine if this is the case, thanks Baoquan for clearing this worry.
> > >
> > > But the other concerns are still need to address, eg. KHO use cases
> > > are not good for kdump.
> > > There could be more to think about.
> > > eg. the issues talked in thread:
> > > https://lore.kernel.org/lkml/Z7dc9Cd8KX3b_brB@dwarf.suse.cz/T/
> >
> > Rethink about this,  other than previous concerns.  Transferring the
> > old kernel state to kdump kernel makes no sense since the old state is
> > not stable as the kernel has crashed.
>
> KHO won't be active for kdump case. The KHO segments are only added to
> kexec_image and never to kexec_crash_image.

Good to know, thanks!

>
> --
> Sincerely yours,
> Mike.
>