[PATCH V2] arm64/hotplug: Improve memory offline event notifier

[Anshuman Khandual]

On 08/24/2020 09:34 AM, Anshuman Khandual wrote:
> This brings about three different changes to the sole memory event notifier
> for arm64 platform and improves it's robustness while also enhancing debug
> capabilities during potential memory offlining error conditions.
> 
> This moves the memory notifier registration bit earlier in the boot process
> from device_initcall() to setup_arch() which will help in guarding against
> potential early boot memory offline requests.
> 
> This enables MEM_OFFLINE memory event handling. It will help intercept any
> possible error condition such as if boot memory some how still got offlined
> even after an expilicit notifier failure, potentially by a future change in
> generic hotplug framework. This would help detect such scenarious and help
> debug further.
> 
> It also adds a validation function which scans entire boot memory and makes
> sure that early memory sections are online. This check is essential for the
> memory notifier to work properly as it cannot prevent boot memory offlining
> if they are not online to begin with. But this additional sanity check is
> enabled only with DEBUG_VM.
> 
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Marc Zyngier <maz at kernel.org>
> Cc: Steve Capper <steve.capper at arm.com>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-kernel at vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
> ---
> This applies on 5.9-rc2
> 
> Changes in V2:
> 
> - Dropped all generic changes wrt MEM_CANCEL_OFFLINE reasons enumeration
> - Dropped all related (processing MEM_CANCEL_OFFLINE reasons) changes on arm64
> - Added validate_boot_mem_online_state() that gets called with early_initcall()
> - Added CONFIG_MEMORY_HOTREMOVE check before registering memory notifier
> - Moved notifier registration i.e memory_hotremove_notifier into setup_arch()
Gentle ping, any updates on this ?