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

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Message-ID: <Z-wDa2aLDKQeetuG@gourry-fedora-PF4VCD3F>
Date: Tue, 1 Apr 2025 11:16:59 -0400
From: Gregory Price <gourry@...rry.net>
To: David Hildenbrand <david@...hat.com>
Cc: dan.j.williams@...el.com, nvdimm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	vishal.l.verma@...el.com, dave.jiang@...el.com,
	linux-cxl@...r.kernel.org
Subject: Re: [PATCH] DAX: warn when kmem regions are truncated for memory
 block alignment.

On Tue, Apr 01, 2025 at 04:50:40PM +0200, David Hildenbrand wrote:
> 
> Oh, you mean with the whole memmap_on_memory thing. Even with that, using
> 2GB memory blocks would only fit a single 1GB memory block ... and it
> requires ZONE_NORMAL.
> 
> For ordinary boot memory, the 1GB behavior should be independent of the
> memory block size (a 1GB page can span multiple blocks as long as they are
> in the same zone), which is the most important thing.
> 
> So I don't think it's a concern for DAX right now. Whoever needs that, can
> disable the memmap_on_memory option.
>

If we think it's not a major issue then I'll rebase onto latest and push
a v9.  I think there was one minor nit left.

I suppose folks can complain to their vendors about alignment if they
don't want 60000 memoryN entries on their huge-memory-systems.

Probably we still want this warning?  Silent truncation still seems
undesirable.

~Gregory