linux-kernel - Re: [PATCH v6 3/3] acpi,srat: give memory block size advice based on CFMWS alignment

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Message-ID: <6733cba395c30_10bc6294df@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 12 Nov 2024 13:41:55 -0800
From: Dan Williams <dan.j.williams@...el.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@...r.kernel.org>, <kernel-team@...a.com>,
	<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>, <gourry@...rry.net>,
	<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>, <david@...hat.com>,
	<osalvador@...e.de>, <gregkh@...uxfoundation.org>,
	<akpm@...ux-foundation.org>, <rppt@...nel.org>
Subject: Re: [PATCH v6 3/3] acpi,srat: give memory block size advice based on
 CFMWS alignment

Gregory Price wrote:
> Capacity is stranded when CFMWS regions are not aligned to block size.
> On x86, block size increases with capacity (2G blocks @ 64G capacity).
> 
> Use CFMWS base/size to report memory block size alignment advice.
> 
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
>  drivers/acpi/numa/srat.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> index 44f91f2c6c5d..34b6993e7d6c 100644
> --- a/drivers/acpi/numa/srat.c
> +++ b/drivers/acpi/numa/srat.c
> @@ -14,6 +14,7 @@
>  #include <linux/errno.h>
>  #include <linux/acpi.h>
>  #include <linux/memblock.h>
> +#include <linux/memory.h>
>  #include <linux/numa.h>
>  #include <linux/nodemask.h>
>  #include <linux/topology.h>
> @@ -338,13 +339,22 @@ static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
>  {
>  	struct acpi_cedt_cfmws *cfmws;
>  	int *fake_pxm = arg;
> -	u64 start, end;
> +	u64 start, end, align;
>  	int node;
>  
>  	cfmws = (struct acpi_cedt_cfmws *)header;
>  	start = cfmws->base_hpa;
>  	end = cfmws->base_hpa + cfmws->window_size;
>  
> +	/* Align memblock size to CFMW regions if possible */
> +	align = 1UL << __ffs(start | end);
> +	if (align >= SZ_256M) {
> +		if (memory_block_advise_max_size(align) < 0)
> +			pr_warn("CFMWS: memblock size advise failed\n");

Oh, this made me go back to look at what happens if CFMWS has multiple
alignment suggestions. Should not memory_block_advise_max_size() be
considering the max advice?

    if (memory_block_advised_size) {
        ...    
    } else {
            memory_block_advised_size = max(memory_block_advised_size, size);
    }

For example, if region0 is an x4 region and region1 is an x1 region then
the memory block size should be 1GB, not 256M. I.e. CFMWS alignment
follows CXL hardware decoder alignment of "256M * InterleaveWays".