linux-kernel - Re: [PATCH 21/26] dax/region: Prevent range mapping allocation on sparse regions

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Date: Wed, 10 Apr 2024 16:02:48 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Navneet Singh <navneet.singh@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Vishal Verma <vishal.l.verma@...el.com>,
	linux-btrfs@...r.kernel.org, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/26] dax/region: Prevent range mapping allocation on
 sparse regions

On Sun, Mar 24, 2024 at 04:18:24PM -0700, Ira Weiny wrote:

Perhaps lead w some words from prior patch to provide context:

"DAX regions mapping dynamic capacity partitions introduce a requirement
for the memory backing the region to come and go as required.  This
results in a DAX region with sparse areas of memory backing."

Or should this fold into: 
dax/region: Create extent resources on DAX region driver load

> Sparse regions are not fully populated with memory and this complicates
> range mapping of dax devices on those regions.  There is no use case for
> range mapping on sparse regions.
> 
> Avoid the complication by prevent range mapping of dax devices on sparse
> regions.

> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  drivers/dax/bus.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index bab19fc578d0..56dddaceeccb 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1452,6 +1452,8 @@ static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
>  		return 0;
>  	if (a == &dev_attr_mapping.attr && is_static(dax_region))
>  		return 0;
> +	if (a == &dev_attr_mapping.attr && is_sparse(dax_region))
> +		return 0;
>  	if ((a == &dev_attr_align.attr ||
>  	     a == &dev_attr_size.attr) && is_static(dax_region))
>  		return 0444;
> 
> -- 
> 2.44.0
>