linux-kernel - Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size

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Message-ID: <039e8c87-c5da-4469-b10e-e57dd5662cff@redhat.com>
Date: Tue, 8 Oct 2024 16:03:37 +0200
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>, linux-cxl@...r.kernel.org,
 x86@...nel.org, linux-mm@...ck.org, linux-acpi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
 luto@...nel.org, peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, hpa@...or.com, osalvador@...e.de, gregkh@...uxfoundation.org,
 rafael@...nel.org, akpm@...ux-foundation.org, dan.j.williams@...el.com,
 Jonathan.Cameron@...wei.com, alison.schofield@...el.com, rrichter@....com,
 terry.bowman@....com, lenb@...nel.org, dave.jiang@...el.com,
 ira.weiny@...el.com
Subject: Re: [PATCH 1/3] memory: extern memory_block_size_bytes and
 set_memory_block_size_order

On 08.10.24 06:43, Gregory Price wrote:
> On CXL systems, block alignment may be as small as 256MB, which may
> require a resize of the block size during initialization.  This is done
> in the ACPI driver, so the resize function need to be made available.
> 
> Presently, only x86 provides the functionality to resize memory
> block sizes.  Wire up a weak stub for set_memory_block_size_order,
> similar to memory_block_size_bytes, that simply returns -ENODEV.
> 
> Since set_memory_block_size_order is now extern, we also need to
> drop the __init macro.
> 
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>   arch/x86/mm/init_64.c  | 2 +-
>   drivers/base/memory.c  | 6 ++++++
>   include/linux/memory.h | 4 ++--
>   3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..6086f99449fa 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1424,7 +1424,7 @@ void mark_rodata_ro(void)
>   
>   /* Adjustable memory block size */
>   static unsigned long set_memory_block_size;
> -int __init set_memory_block_size_order(unsigned int order)
> +int set_memory_block_size_order(unsigned int order)
>   {
>   	unsigned long size = 1UL << order;
>   
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 67858eeb92ed..f9045642f69e 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -110,6 +110,12 @@ static void memory_block_release(struct device *dev)
>   	kfree(mem);
>   }
>   
> +int __weak set_memory_block_size_order(unsigned int order)
> +{
> +	return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(set_memory_block_size_order);

I can understand what you are trying to achieve, but letting arbitrary 
modules mess with this sounds like a bad idea.

-- 
Cheers,

David / dhildenb