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

[Andrew Morton]

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