linux-kernel - Re: [PATCH v2 1/1] libnvdimm/e820: Add a new parameter to configure many regions per e820 entry

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Message-ID: <6805a8382627f_18b6012946a@iweiny-mobl.notmuch>
Date: Sun, 20 Apr 2025 21:06:48 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Michal Clapinski <mclapinski@...gle.com>, Pasha Tatashin
	<pasha.tatashin@...een.com>, Dan Williams <dan.j.williams@...el.com>, "Vishal
 Verma" <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, "Ira
 Weiny" <ira.weiny@...el.com>, Jonathan Corbet <corbet@....net>
CC: <nvdimm@...ts.linux.dev>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Michal Clapinski <mclapinski@...gle.com>
Subject: Re: [PATCH v2 1/1] libnvdimm/e820: Add a new parameter to configure
 many regions per e820 entry

Michal Clapinski wrote:
> Currently, the user has to specify each memory region to be used with
> nvdimm via the memmap parameter. Due to the character limit of the
> command line, this makes it impossible to have a lot of pmem devices.
> This new parameter solves this issue by allowing users to divide
> one e820 entry into many nvdimm regions.
> 
> This change is needed for the hypervisor live update. VMs' memory will
> be backed by those emulated pmem devices. To support various VM shapes
> I want to create devdax devices at 1GB granularity similar to hugetlb.

Why is it not sufficient to create a region out of a single memmap range
and create multiple 1G dax devices within that single range?

Ira

> 
> It's also possible to expand this parameter in the future,
> e.g. to specify the type of the device (fsdax/devdax).
> 
> Signed-off-by: Michal Clapinski <mclapinski@...gle.com>

[snip]