[PATCH V2] arm64/hotplug: Improve memory offline event notifier
catalin.marinas at arm.com
Fri Sep 11 10:06:04 EDT 2020
On Mon, Aug 24, 2020 at 09:34:29AM +0530, 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.
Could you please split this in separate patches rather than having a
single one doing three somewhat related things?
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -376,6 +376,14 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
> "This indicates a broken bootloader or old kernel\n",
> boot_args, boot_args, boot_args);
> + /*
> + * Register the memory notifier which will prevent boot
> + * memory offlining requests - early enough. But there
> + * should not be any actual offlinig request till memory
> + * block devices are initialized with memory_dev_init().
> + */
> + memory_hotremove_notifier();
Why can this not be an early_initcall()? As you said, memory_dev_init()
is called much later, after the SMP was initialised.
You could even combine this with validate_bootmem_online_state() in a
single early_initcall() which, after checking, registers the notifier.
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