linux-kernel - Re: [PATCH v1] memory tier: consolidate the initialization of memory tiers

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Date: Fri, 21 Jun 2024 18:34:13 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Ho-Ren (Jack) Chuang" <horen.chuang@...ux.dev>
Cc: "Jonathan Cameron" <Jonathan.Cameron@...wei.com>, "Huang, Ying"
 <ying.huang@...el.com>, "Gregory Price" <gourry.memverge@...il.com>,
 aneesh.kumar@...ux.ibm.com, mhocko@...e.com, tj@...nel.org,
 john@...alactic.com, "Eishan Mirakhur" <emirakhur@...ron.com>,
 "Vinicius Tavares Petrucci" <vtavarespetr@...ron.com>, "Ravis OpenSrc"
 <Ravis.OpenSrc@...ron.com>, "Alistair Popple" <apopple@...dia.com>,
 "Srinivasulu Thanneeru" <sthanneeru@...ron.com>, "SeongJae Park"
 <sj@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown
 <lenb@...nel.org>, Dave Jiang <dave.jiang@...el.com>, Dan Williams
 <dan.j.williams@...el.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, "Ho-Ren (Jack) Chuang" <horenc@...edu>,
 "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com>, "Ho-Ren (Jack) Chuang"
 <horenchuang@...il.com>, linux-cxl@...r.kernel.org, qemu-devel@...gnu.org
Subject: Re: [PATCH v1] memory tier: consolidate the initialization of
 memory tiers

On Fri, 21 Jun 2024 04:48:30 +0000 "Ho-Ren (Jack) Chuang" <horen.chuang@...ux.dev> wrote:

> If we simply move the set_node_memory_tier() from memory_tier_init() to
> late_initcall(), it will result in HMAT not registering the
> mt_adistance_algorithm callback function,

Immediate reaction: then don't do that!

> because set_node_memory_tier()
> is not performed during the memory tiering initialization phase,
> leading to a lack of correct default_dram information.
> 
> Therefore, we introduced a nodemask to pass the information of the
> default DRAM nodes. The reason for not choosing to reuse
> default_dram_type->nodes is that it is not clean enough. So in the end,
> we use a __initdata variable, which is a variable that is released once
> initialization is complete, including both CPU and memory nodes for HMAT
> to iterate through.
> 
> Besides, since default_dram_type may be checked/used during the
> initialization process of HMAT and drivers, it is better to keep the
> allocation of default_dram_type in memory_tier_init().

What is this patch actually aiming to do?  Is it merely a code cleanup,
or are there functional changes?

> Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@...edance.com>
> ---
> Hi all,
> 
> The current memory tier initialization process is distributed across two
> different functions, memory_tier_init() and memory_tier_late_init(). This
> design is hard to maintain. Thus, this patch is proposed to reduce the
> possible code paths by consolidating different initialization patches into one.

Ah, there it is.  Please make this the opening paragraph, not an aside
buried below the ^---$.

I'll await review input before proceeding with this, thanks.