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

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Date: Tue, 25 Jun 2024 06:24:11 +0000
From: horen.chuang@...ux.dev
To: "Andrew Morton" <akpm@...ux-foundation.org>
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>, 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

June 21, 2024 at 6:34 PM, "Andrew Morton" <akpm@...ux-foundation.org> wrote:

Hi Andrew,

Thanks for the feedback. I will send a v2 with the patch description
written in a cover letter.

> 
> 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.
>