linux-kernel - Re: [PATCH] mm/memory_hotplug: fix memmap_on

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Date: Wed, 10 Jan 2024 17:15:38 +0100
From: David Hildenbrand <david@...hat.com>
To: Sumanth Korikkar <sumanthk@...ux.ibm.com>, linux-mm <linux-mm@...ck.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc: Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 linux-s390 <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/memory_hotplug: fix memmap_on_memory sysfs value
 retrieval

On 10.01.24 15:01, Sumanth Korikkar wrote:
> The set_memmap_mode() function stores the kernel parameter memmap mode
> as an integer. However, the get_memmap_mode() function utilizes
> param_get_bool() to fetch the value as a boolean, leading to potential
> endianness issue. On Big-endian architectures, the memmap_on_memory is
> consistently displayed as 'N' regardless of its actual status.
> 
> To address this endianness problem, the solution involves obtaining the
> mode as an integer. This adjustment ensures the proper display of the
> memmap_on_memory parameter, presenting it as one of the following
> options: Force, Y, or N.
> 
> Fixes: 2d1f649c7c08 ("mm/memory_hotplug: support memmap_on_memory when memmap is not aligned to pageblocks")
> Suggested-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
> Cc: <stable@...r.kernel.org> # v6.6+
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
>   mm/memory_hotplug.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b944e8bf1911..707027f69150 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -101,9 +101,11 @@ static int set_memmap_mode(const char *val, const struct kernel_param *kp)
>   
>   static int get_memmap_mode(char *buffer, const struct kernel_param *kp)
>   {
> -	if (*((int *)kp->arg) == MEMMAP_ON_MEMORY_FORCE)
> -		return sprintf(buffer,  "force\n");
> -	return param_get_bool(buffer, kp);
> +	int mode = *((int *)kp->arg);
> +
> +	if (mode == MEMMAP_ON_MEMORY_FORCE)
> +		return sprintf(buffer, "force\n");
> +	return sprintf(buffer, "%c\n", mode ? 'Y' : 'N');
>   }

I was wondering if we want to return "Y" instead of "force". But using 
force seems more consistent.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb