linux-kernel - Re: [PATCH] ACPI: NUMA: Process hotpluggable memblocks when !CONFIG_MEMORY

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Date:   Fri, 17 Dec 2021 19:12:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Igor Mammedov <imammedo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] ACPI: NUMA: Process hotpluggable memblocks when !CONFIG_MEMORY_HOTPLUG

On Thu, Dec 16, 2021 at 10:58 AM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> Some systems (e.g. Hyper-V guests) have all their memory marked as
> hotpluggable in SRAT. acpi_numa_memory_affinity_init(), however,
> ignores all such regions when !CONFIG_MEMORY_HOTPLUG and this is
> unfortunate as memory affinity (NUMA) information gets lost.
>
> 'Hot Pluggable' flag in SRAT only means that "system hardware supports
> hot-add and hot-remove of this memory region", it doesn't prevent
> memory from being cold-plugged there.
>
> Ignore 'Hot Pluggable' bit instead of skipping the whole memory
> affinity information when !CONFIG_MEMORY_HOTPLUG.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>

Makes sense to me, so applied as 5.17 material, but CC Dan and
Jonathan in case this can be problematic for some mm-related reason.

> ---
>  drivers/acpi/numa/srat.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> index b8795fc49097..6c884f3e8332 100644
> --- a/drivers/acpi/numa/srat.c
> +++ b/drivers/acpi/numa/srat.c
> @@ -254,9 +254,8 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
>         }
>         if ((ma->flags & ACPI_SRAT_MEM_ENABLED) == 0)
>                 goto out_err;
> -       hotpluggable = ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE;
> -       if (hotpluggable && !IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> -               goto out_err;
> +       hotpluggable = IS_ENABLED(CONFIG_MEMORY_HOTPLUG) &&
> +               (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE);
>
>         start = ma->base_address;
>         end = start + ma->length;
> --
> 2.33.1
>