linux-kernel - Re: [PATCH v2 3/7] mm,memory_hotplug: Add kernel boot option to enable memmap_on

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Date:   Thu, 25 Feb 2021 19:25:58 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>, VlastimilBabkavbabka@...e.cz,
        pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v2 3/7] mm,memory_hotplug: Add kernel boot option to
 enable memmap_on_memory

> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9bcc460e8bfe..95695483a622 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -42,7 +42,31 @@
>   #include "internal.h"
>   #include "shuffle.h"
>   
> -static bool memmap_on_memory_enabled;
> +/*
> + * memory_hotplug.memmap_on_memory parameter
> + */
> +static bool memmap_on_memory_enabled __ro_after_init;
> +
> +static int memmap_on_memory_show(char *buffer, const struct kernel_param *kp)
> +{
> +	return sprintf(buffer, "%s\n",
> +		       memmap_on_memory_enabled ? "on" : "off");
> +}
> +
> +static __meminit int memmap_on_memory_store(const char *val,
> +					    const struct kernel_param *kp)
> +{
> +	/*
> +	 * Fail silently in case we cannot enable it due to platform constraints.
> +	 * User can always check whether it is enabled or not via /sys/module.
> +	 */
> +	if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE))
> +		return 0;
> +
> +	return param_set_bool(val, kp);
> +}
> +module_param_call(memmap_on_memory, memmap_on_memory_store,
> +		  memmap_on_memory_show, &memmap_on_memory_enabled, 0400);

Why are other users not allowed to read?

>   

Might want to add a MODULE_PARM_DESC().


As we fail silently already, I'd keep it simple and use a

module_param(memmap_on_memory, bool, 0444);

moving the IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE) into the 
runtime check.


Apart from that LGTM.

-- 
Thanks,

David / dhildenb