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

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Message-ID: <CALu+AoRdfjNcjweq_ipxCC6UGBzM-a5ma417RBr-C3EQ=Em9OQ@mail.gmail.com>
Date: Wed, 26 Mar 2025 17:17:16 +0800
From: Dave Young <dyoung@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: Changyuan Lyu <changyuanl@...gle.com>, linux-kernel@...r.kernel.org, graf@...zon.com, 
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	linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v5 11/16] kexec: add config option for KHO

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.