linux-kernel - Re: [RFC PATCH v3 1/2] mm: numa_memblks: introduce numa_add_reserved

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Message-ID: <67e48eb87206f_13cb2944b@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Date: Wed, 26 Mar 2025 19:33:12 -0400
From: Dan Williams <dan.j.williams@...el.com>
To: Yuquan Wang <wangyuquan1236@...tium.com.cn>,
	<Jonathan.Cameron@...wei.com>, <dan.j.williams@...el.com>, <rppt@...nel.org>,
	<akpm@...ux-foundation.org>, <david@...hat.com>, <bfaccini@...dia.com>,
	<rafael@...nel.org>, <lenb@...nel.org>, <dave@...olabs.net>,
	<dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <ira.weiny@...el.com>, <rrichter@....com>,
	<haibo1.xu@...el.com>
CC: <linux-acpi@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <chenbaozi@...tium.com.cn>, Yuquan Wang
	<wangyuquan1236@...tium.com.cn>
Subject: Re: [RFC PATCH v3 1/2] mm: numa_memblks: introduce
 numa_add_reserved_memblk

Yuquan Wang wrote:
> With numa_add_reserved_memblk(), kernel could add numa_memblk into
> numa_reserved_meminfo directly.
> 
> In previous, such process relies on numa_add_memblk() adding to
> numa_meminfo list first and then uses numa_move_tail_memblk() to
> move one from numa_meminfo to numa_reserved_meminfo.

I would explicitly state the motivation and the use case for the patch.

---
acpi_parse_cfmws() currently adds empty CFMWS ranges to numa_meminfo
with the expectation that numa_cleanup_meminfo moves them to
numa_reserved_meminfo. There is no need for that indirection when it is
known in advance that these unpopulated ranges are meant for
numa_reserved_meminfo in suppot of future hotplug / CXL provisioning.
---

> 
> Signed-off-by: Yuquan Wang <wangyuquan1236@...tium.com.cn>
> ---
>  include/linux/numa_memblks.h |  1 +
>  mm/numa_memblks.c            | 16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/numa_memblks.h b/include/linux/numa_memblks.h
> index dd85613cdd86..991076cba7c5 100644
> --- a/include/linux/numa_memblks.h
> +++ b/include/linux/numa_memblks.h
> @@ -22,6 +22,7 @@ struct numa_meminfo {
>  };
>  
>  int __init numa_add_memblk(int nodeid, u64 start, u64 end);
> +int __init numa_add_reserved_memblk(int nid, u64 start, u64 end);
>  void __init numa_remove_memblk_from(int idx, struct numa_meminfo *mi);
>  
>  int __init numa_cleanup_meminfo(struct numa_meminfo *mi);
> diff --git a/mm/numa_memblks.c b/mm/numa_memblks.c
> index ff4054f4334d..e70c76cc46dd 100644
> --- a/mm/numa_memblks.c
> +++ b/mm/numa_memblks.c
> @@ -200,6 +200,22 @@ int __init numa_add_memblk(int nid, u64 start, u64 end)
>  	return numa_add_memblk_to(nid, start, end, &numa_meminfo);
>  }
>  
> +/**
> + * numa_add_reserved_memblk - Add one numa_memblk to numa_reserved_meminfo
> + * @nid: NUMA node ID of the new memblk
> + * @start: Start address of the new memblk
> + * @end: End address of the new memblk
> + *
> + * Add a new memblk to the numa_reserved_meminfo.

I would say a bit more here about when to use this function. Something
like:

"numa_cleanup_meminfo() reconciles all numa_memblk instances against
memblock_type information and moves any that intersect reserved ranges
to numa_reserved_meminfo. However, when that information is known ahead
of time add the numa_memblk to numa_reserved_meminfo directly."

With those 2 suggestions you can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>