linux-kernel - Re: [PATCH v9 07/19] cxl/region: Add sparse DAX region support

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Message-ID: <20250414164050.00003d6c@huawei.com>
Date: Mon, 14 Apr 2025 16:40:50 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Dan
 Williams" <dan.j.williams@...el.com>, Davidlohr Bueso <dave@...olabs.net>,
	Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, <linux-cxl@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 07/19] cxl/region: Add sparse DAX region support

On Sun, 13 Apr 2025 17:52:15 -0500
Ira Weiny <ira.weiny@...el.com> wrote:

> Dynamic Capacity CXL regions must allow memory to be added or removed
> dynamically.  In addition to the quantity of memory available the
> location of the memory within a DC partition is dynamic based on the
> extents offered by a device.  CXL DAX regions must accommodate the
> sparseness of this memory in the management of DAX regions and devices.
> 
> Introduce the concept of a sparse DAX region.  Introduce
> create_dynamic_ram_a_region() sysfs entry to create such regions.
> Special case dynamic capable regions to create a 0 sized seed DAX device
> to maintain compatibility which requires a default DAX device to hold a
> region reference.
> 
> Indicate 0 byte available capacity until such time that capacity is
> added.
> 
> Sparse regions complicate the range mapping of dax devices.  There is no
> known use case for range mapping on sparse regions.  Avoid the
> complication by preventing range mapping of dax devices on sparse
> regions.
> 
> Interleaving is deferred for now.  Add checks.
> 
> Based on an original patch by Navneet Singh.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
>
I'm not that familiar with the DAX parts but looks fine to me.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>