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

[David Hildenbrand <david@redhat.com>]

On 22.10.24 23:34, 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);
>   }
>   
> +/*


As Mike says, this documentation looks incomplete.

/**
  * memory_block_advise_max_size: suggest a maximum memory block size
  ...

> + * @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

Missing space after "size."

> + * 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)
> +{
> +	if (!bz || (bz & (bz - 1)) != 0)
> +		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;
> +}
> +
> +/*
> + * 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)

Can we call that "memory_block_advised_max_size()" ?

> +{
> +	memory_block_size_probed = true;

Call this "memory_block_advised_size_queried" ?

> +	return memory_block_advised_sz;
> +}



-- 
Cheers,

David / dhildenb