linux-kernel - Re: [v1 0/5] allow to reserve memory for normal kexec kernel

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Date:   Tue, 9 Jul 2019 16:06:05 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     James Morris <jmorris@...ei.org>, sashal@...nel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v1 0/5] allow to reserve memory for normal kexec kernel

Hi Pavel,

On Tue, Jul 9, 2019 at 2:46 AM Pavel Tatashin <pasha.tatashin@...een.com> wrote:
>
> Currently, it is only allowed to reserve memory for crash kernel, because
> it is a requirement in order to be able to boot into crash kernel without
> touching memory of crashed kernel is to have memory reserved.
>
> The second benefit for having memory reserved for kexec kernel is
> that it does not require a relocation after segments are loaded into
> memory.
>
> If kexec functionality is used for a fast system update, with a minimal
> downtime, the relocation of kernel + initramfs might take a significant
> portion of reboot.
>
> In fact, on the machine that we are using, that has ARM64 processor
> it takes 0.35s to relocate during kexec, thus taking 52% of kernel reboot
> time:
>
> kernel shutdown 0.03s
> relocation      0.35s
> kernel startup  0.29s
>
> Image: 13M and initramfs is 24M. If initramfs increases, the relocation
> time increases proportionally.
>
> While, it is possible to add 'kexeckernel=' parameters support to other
> architectures by modifying reserve_crashkernel(), in this series this is
> done for arm64 only.
>
> Pavel Tatashin (5):
>   kexec: quiet down kexec reboot
>   kexec: add resource for normal kexec region
>   kexec: export common crashkernel/kexeckernel parser
>   kexec: use reserved memory for normal kexec reboot
>   arm64, kexec: reserve kexeckernel region
>
>  .../admin-guide/kernel-parameters.txt         |  7 ++
>  arch/arm64/kernel/setup.c                     |  5 ++
>  arch/arm64/mm/init.c                          | 83 ++++++++++++-------
>  include/linux/crash_core.h                    |  6 ++
>  include/linux/ioport.h                        |  1 +
>  include/linux/kexec.h                         |  6 +-
>  kernel/crash_core.c                           | 27 +++---
>  kernel/kexec_core.c                           | 50 +++++++----
>  8 files changed, 127 insertions(+), 58 deletions(-)
>
> --
> 2.22.0

This seems like an issue with time spent while doing sha256
verification while in purgatory.

Can you please try the following two patches which enable D-cache in
purgatory before SHA verification and disable it before switching to
kernel:

http://lists.infradead.org/pipermail/kexec/2017-May/018839.html
http://lists.infradead.org/pipermail/kexec/2017-May/018840.html

Note that these were not accepted upstream but are included in several
distros in some form or the other :)

Thanks,
Bhupesh