linux-kernel - Re: [PATCH v3 0/2] libnvdimm/e820: Add a new parameter to configure many regions per e820 entry

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Message-ID: <685c67525ba79_2c35442945@iweiny-mobl.notmuch>
Date: Wed, 25 Jun 2025 16:17:06 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Michal Clapinski <mclapinski@...gle.com>, Jonathan Corbet
	<corbet@....net>, 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>, <nvdimm@...ts.linux.dev>
CC: "Paul E. McKenney" <paulmck@...nel.org>, Thomas Huth <thuth@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, Steven Rostedt
	<rostedt@...dmis.org>, "Borislav Petkov (AMD)" <bp@...en8.de>, Ard Biesheuvel
	<ardb@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Pasha
 Tatashin" <pasha.tatashin@...een.com>, Mike Rapoport <rppt@...nel.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>, Michal Clapinski <mclapinski@...gle.com>
Subject: Re: [PATCH v3 0/2] libnvdimm/e820: Add a new parameter to configure
 many regions per e820 entry

Michal Clapinski wrote:
> This includes:
> 1. Splitting one e820 entry into many regions.
> 2. Conversion to devdax during boot.
> 
> 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.
> Also detecting those devices as devdax during boot speeds up the whole
> process. Conversion in userspace would be much slower which is
> unacceptable while trying to minimize

Did you explore the NFIT injection strategy which Dan suggested?[1]

[1] https://lore.kernel.org/all/6807f0bfbe589_71fe2944d@dwillia2-xfh.jf.intel.com.notmuch/

If so why did it not work?

Ira

[snip]