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

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@arm.com>
Cc: Will Deacon <redacted>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Steve Capper <redacted>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
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 ?

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