linux-kernel - Re: [PATCH v2 2/3] x86: probe memblock size advisement value during mm init

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Message-ID: <7b877356-f5c5-4996-904b-6c3b71389255@redhat.com>
Date: Mon, 21 Oct 2024 13:12:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, linux-mm@...ck.org
Cc: dan.j.williams@...el.com, ira.weiny@...el.com,
 dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
 rafael@...nel.org, lenb@...nel.org, rppt@...nel.org,
 akpm@...ux-foundation.org, alison.schofield@...el.com,
 Jonathan.Cameron@...wei.com, rrichter@....com, ytcoode@...il.com,
 haibo1.xu@...el.com, dave.jiang@...el.com
Subject: Re: [PATCH v2 2/3] x86: probe memblock size advisement value during
 mm init



Am 16.10.24 um 21:24 schrieb Gregory Price:
> Systems with hotplug may provide an advisement value on what the
> memblock size should be.  Probe this value when the rest of the
> configuration values are considered.
> 
> The new heuristic is as follows
> 
> 1) set_memory_block_size_order value if already set (cmdline param)
> 2) minimum block size if memory is less than large block limit
> 3) [new] hotplug advise: lesser of advise value or memory alignment
> 4) Max block size if system is bare-metal
> 5) Largest size that aligns to end of memory.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>   arch/x86/mm/init_64.c | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..b72923b12d99 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1439,6 +1439,7 @@ static unsigned long probe_memory_block_size(void)
>   {
>   	unsigned long boot_mem_end = max_pfn << PAGE_SHIFT;
>   	unsigned long bz;
> +	int order;
>   
>   	/* If memory block size has been set, then use it */
>   	bz = set_memory_block_size;
> @@ -1451,6 +1452,21 @@ static unsigned long probe_memory_block_size(void)
>   		goto done;
>   	}
>   
> +	/* Consider hotplug advisement value (if set) */
> +	order = memblock_probe_size_order();

"size_order" is a very weird name. Just return a size?

memory_block_advised_max_size()

or sth like that?

> +	bz = order > 0 ? (1UL << order) : 0;
> +	if (bz) {
> +		/* Align down to max and up to min supported */
> +		bz = 
> +		/* Use lesser of advisement and end of memory alignment */
> +		for (; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
> +			if (IS_ALIGNED(boot_mem_end, bz))
> +				goto done;

This looks like duplicate code wit the loop below.

Could we refactored it into something like:

advised_max_size = memory_block_advised_max_size();
if (!advised_max_size) {
	bz = MAX_BLOCK_SIZE;
	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)
		goto done,
} else {
	bz = max(min(advised_max_size, MAX_BLOCK_SIZE), MIN_MEMORY_BLOCK_SIZE);
}

for (; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {
	if (IS_ALIGNED(boot_mem_end, bz))
		break;



-- 
Cheers,

David / dhildenb