linux-kernel - Re: [PATCH] acpi/hmat,mm/memtier: always register hmat adist calculation callback

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Message-ID: <ZqlMXuBxi2oShb-u@PC2K9PVX.TheFacebook.com>
Date: Tue, 30 Jul 2024 16:26:06 -0400
From: Gregory Price <gourry@...rry.net>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, dave.jiang@...el.com,
	Jonathan.Cameron@...wei.com, horenchuang@...edance.com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	dan.j.williams@...el.com, lenb@...nel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH] acpi/hmat,mm/memtier: always register hmat adist
 calculation callback

On Wed, Jul 31, 2024 at 03:20:37PM +0800, Huang, Ying wrote:
> Gregory Price <gourry@...rry.net> writes:
> >
> > In this case, the system is configured explicitly so that kmem does not
> > manage it. In fact, some systems still cannot be managed with
> > EFI_MEMORY_SP due to hpa!=spa issues that the driver cannot manage.
> 
> Sorry, I don't understand.  IIUC, kmem.c can manage almost any memory
> range via drivers/dax/hmem.  Please check
> 
> drivers/dax/hmem/device.c
> drivers/dax/hmem/hmem.c
> 
> Could you elaborate why kmem.c doesn't work for some memory range?
> 

Sorry I misunderstood, I thought you meant the cxl+kmem/hmem subsystem
interaction and handing configuration of the CXL device over to the
kernel.

The boot parameter is not likely to be a solution for us but I will look
at it.

> > But I think a feature that worked in 5.x should work in 6.x, and right
> > now the change in node placement breaks hardware that worked with 5.x
> > which happened to have broken or missing HMAT.