linux-kernel - Re: [PATCH v3 14/17] cxl: docs/allocation/page-allocator

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Message-ID: <aCI5c_hIS8bWgAaC@gourry-fedora-PF4VCD3F>
Date: Mon, 12 May 2025 14:09:55 -0400
From: Gregory Price <gourry@...rry.net>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-cxl@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	dave@...olabs.net, jonathan.cameron@...wei.com,
	dave.jiang@...el.com, alison.schofield@...el.com,
	vishal.l.verma@...el.com, ira.weiny@...el.com,
	dan.j.williams@...el.com, corbet@....net
Subject: Re: [PATCH v3 14/17] cxl: docs/allocation/page-allocator

On Mon, May 12, 2025 at 06:52:31PM +0100, Matthew Wilcox wrote:
> > 
> > Feel free to submit patches that deletes the existing code if you want
> > it removed from the documentation.
> 
> Who sneaked that in when?

The ACPI and EFI folks when they allowed for CXL memory to be marked 
EFI_CONVENTIONAL_MEMORY - which means Linux can't actually differentiate
between DRAM and CXL during __init and brings it online in the page
allocator as SystemRAM in ZONE_NORMAL (attached to the NUMA node that
maps to the Proximity Domain in the SRAT).

Not sure there's anything you can do about that.

And for DAX:

09d09e04d2 (cxl/dax: Create dax devices for CXL RAM regions)

Which allows for EFI_MEMORY_SP / Soft Reserved CXL regions to be brought
up as a DAX devices (which can be bound to SystemRAM via DAX kmem).

Wasn't much sneaking going on here - DAX kmem has been around and hacked
on since 2019, and probably some years before that.

~Gregory