linux-kernel - Re: [PATCH v3 2/3] x86: probe memory block size advisement value during mm init

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Message-ID: <07102ea5-ee43-4c11-ab3c-a35cfce9003b@redhat.com>
Date: Tue, 29 Oct 2024 13:40:38 +0100
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: linux-cxl@...ck.org, Jonathan.Cameron@...wei.com,
 dan.j.williams@...el.com, rrichter@....com, Terry.Bowman@....com,
 dave.jiang@...el.com, ira.weiny@...el.com, alison.schofield@...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, osalvador@...e.de,
 gregkh@...uxfoundation.org, akpm@...ux-foundation.org, rppt@...nel.org
Subject: Re: [PATCH v3 2/3] x86: probe memory block size advisement value
 during mm init

On 22.10.24 23:34, Gregory Price wrote:
> 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) if no hotplug advice: Max block size if system is bare-metal,
>     otherwise use end of memory alignment.
> 4) if hotplug advice: lesser of advice and end of memory alignment.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>   arch/x86/mm/init_64.c | 14 +++++++++-----
>   1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..93d669f467f7 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1452,13 +1452,17 @@ static unsigned long probe_memory_block_size(void)
>   	}
>   
>   	/*
> -	 * Use max block size to minimize overhead on bare metal, where
> -	 * alignment for memory hotplug isn't a concern.
> +	 * When hotplug alignment is not a concern, maximize blocksize
> +	 * to minimize overhead. Otherwise, align to the lesser of advice
> +	 * alignment and end of memory alignment.
>   	 */
> -	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
> +	bz = memory_block_probe_max_size();
> +	if (!bz) {
>   		bz = MAX_BLOCK_SIZE;
> -		goto done;
> -	}
> +		if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
> +			goto done;
> +	} else
> +		bz = max(min(bz, MAX_BLOCK_SIZE), MIN_MEMORY_BLOCK_SIZE);
>   
>   	/* Find the largest allowed block size that aligns to memory end */
>   	for (bz = MAX_BLOCK_SIZE; bz > MIN_MEMORY_BLOCK_SIZE; bz >>= 1) {


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

-- 
Cheers,

David / dhildenb