Re: [PATCH v3 1/3] memory: implement memory_block_advise/probe_max_size

[Mike Rapoport <rppt@kernel.org>]

Hi,

On Tue, Oct 22, 2024 at 05:34:48PM -0400, Gregory Price wrote:
> Hotplug memory sources may have opinions on what the memblock size
> should be - usually for alignment purposes.  For example, CXL memory
> extents can be 256MB with a matching alignment. If this size/alignment
> is smaller than the block size, it can result in stranded capacity.
> 
> Implement memory_block_advise_max_size for use prior to allocator init,
> for software to advise the system on the max block size.
> 
> Implement memory_block_probe_max_size for use by arch init code to
> calculate the best block size. Use of advice is architecture defined.
> 
> The probe value can never change after first probe. Calls to advise
> after probe will return -EBUSY to aid debugging.
> 
> On systems without hotplug, always return -ENODEV and 0 respectively.
> 
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
>  drivers/base/memory.c  | 43 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/memory.h | 10 ++++++++++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 67858eeb92ed..a0fd9e1451aa 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -110,6 +110,49 @@ static void memory_block_release(struct device *dev)
>  	kfree(mem);
>  }
>  
> +/*

If the intention for this to be a kernel-doc comment it should start with
/**, should be placed right before the documented function and start with a
brief function description

> + * @size: suggestion for maximum block size. must be aligned on power of 2.
> + *
> + * Early boot software (pre-allocator init) may advise archs on the max block
> + * size.This value can only decrease after initialization, as the intent is to
> + * identify the largest supported alignment for all sources.
> + *
> + * Use of this value is arch dependent, as is min/max block size.
> + *
> + * Returns: 0 on success
> + *	    -EINVAL if size is 0 or not pow2 aligned
> + *	    -EBUSY if value has already been probed
> + */
> +static size_t memory_block_advised_sz;
> +static bool memory_block_size_probed;
> +int memory_block_advise_max_size(size_t bz)

size seems to me a better parameter name :)

> +{
> +	if (!bz || (bz & (bz - 1)) != 0)

we have is_power_of_2()

> +		return -EINVAL;
> +
> +	if (memory_block_size_probed)
> +		return -EBUSY;
> +
> +	if (memory_block_advised_sz)
> +		memory_block_advised_sz = min(bz, memory_block_advised_sz);
> +	else
> +		memory_block_advised_sz = bz;
> +
> +	return 0;
> +}
> +
> +/*

should it be kernel-doc?

> + * memory_block_probe_max_size provides a suggested maximum memory block
> + * size value. After the first call, the value can never change.
> + *
> + * Returns: advised size in bytes, or 0 if never set.
> + */
> +size_t memory_block_probe_max_size(void)
> +{
> +	memory_block_size_probed = true;
> +	return memory_block_advised_sz;
> +}
> +
>  unsigned long __weak memory_block_size_bytes(void)
>  {
>  	return MIN_MEMORY_BLOCK_SIZE;
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index c0afee5d126e..47c00d6e1165 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -149,6 +149,14 @@ static inline int hotplug_memory_notifier(notifier_fn_t fn, int pri)
>  {
>  	return 0;
>  }
> +static inline int memory_block_advise_max_size(size_t size)
> +{
> +	return -ENODEV;
> +}
> +static inline size_t memory_block_probe_max_size(void)
> +{
> +	return 0;
> +}
>  #else /* CONFIG_MEMORY_HOTPLUG */
>  extern int register_memory_notifier(struct notifier_block *nb);
>  extern void unregister_memory_notifier(struct notifier_block *nb);
> @@ -181,6 +189,8 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
>  void memory_block_add_nid(struct memory_block *mem, int nid,
>  			  enum meminit_context context);
>  #endif /* CONFIG_NUMA */
> +int memory_block_advise_max_size(size_t size);
> +size_t memory_block_probe_max_size(void);
>  #endif	/* CONFIG_MEMORY_HOTPLUG */
>  
>  /*
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.