linux-kernel - Re: [PATCH v5 11/16] kexec: add config option for KHO

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Message-ID: <Z-Pk9Bnr0lDVopKj@kernel.org>
Date: Wed, 26 Mar 2025 07:28:52 -0400
From: Mike Rapoport <rppt@...nel.org>
To: Dave Young <dyoung@...hat.com>
Cc: Baoquan He <bhe@...hat.com>, Changyuan Lyu <changyuanl@...gle.com>,
	linux-kernel@...r.kernel.org, graf@...zon.com,
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Subject: Re: [PATCH v5 11/16] kexec: add config option for KHO

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@...hat.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. 

-- 
Sincerely yours,
Mike.