linux-kernel - Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory block alignment.

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Message-ID: <Z_bzAapzjzFR3u_P@aschofie-mobl2.lan>
Date: Wed, 9 Apr 2025 15:21:53 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Gregory Price <gourry@...rry.net>
CC: <linux-cxl@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <kernel-team@...a.com>,
	<dan.j.williams@...el.com>, <vishal.l.verma@...el.com>,
	<dave.jiang@...el.com>, David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v2] DAX: warn when kmem regions are truncated for memory
 block alignment.

On Tue, Apr 01, 2025 at 09:59:20PM -0400, Gregory Price wrote:
> Device capacity intended for use as system ram should be aligned to the
> archite-defined memory block size or that capacity will be silently
> truncated and capacity stranded.
> 
> As hotplug dax memory becomes more prevelant, the memory block size
> alignment becomes more important for platform and device vendors to
> pay attention to - so this truncation should not be silent.
> 
> This issue is particularly relevant for CXL Dynamic Capacity devices,
> whose capacity may arrive in spec-aligned but block-misaligned chunks.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Gregory Price <gourry@...rry.net>

Existing unit test 'daxctl-devices.sh' hits this case:
[   52.547521] kmem dax3.0: DAX region truncated by 62.0 MiB due to alignment

Tested-by: Alison Schofield <alison.schofield@...el.com>

snip

>