On Tue, 29 Oct 2024 15:34:58 -0500
ira.weiny@xxxxxxxxx wrote:
> From: Navneet Singh <navneet.singh@xxxxxxxxx>
>
> DAX regions which map dynamic capacity partitions require that memory be
> allowed to come and go. Recall sparse regions were created for this
> purpose. Now that extents can be realized within DAX regions the DAX
> region driver can start tracking sub-resource information.
>
> The tight relationship between DAX region operations and extent
> operations require memory changes to be controlled synchronously with
> the user of the region. Synchronize through the dax_region_rwsem and by
> having the region driver drive both the region device as well as the
> extent sub-devices.
>
> Recall requests to remove extents can happen at any time and that a host
> is not obligated to release the memory until it is not being used. If
> an extent is not used allow a release response.
>
> When extents are eligible for release. No mappings exist but data may
> reside in caches not yet written to the device. Call
> cxl_region_invalidate_memregion() to write back data to the device prior
> to signaling the release complete. This is inefficient but is the best
> we can do at the moment and should occur infrequently with sufficiently
> large extents and work loads.
>
> The DAX layer has no need for the details of the CXL memory extent
> devices. Expose extents to the DAX layer as device children of the DAX
> region device. A single callback from the driver aids the DAX layer to
> determine if the child device is an extent. The DAX layer also
> registers a devres function to automatically clean up when the device is
> removed from the region.
>
> There is a race between extents being surfaced and the dax_cxl driver
> being loaded. The driver must therefore scan for any existing extents
> while still under the device lock.
>
> Respond to extent notifications. Manage the DAX region resource tree
> based on the extents lifetime. Return the status of remove
> notifications to lower layers such that it can manage the hardware
> appropriately.
>
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
One typo spotted.
Otherwise seems fine to me but not an area I know well yet!
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> index 0867115aeef2e1b2d4c88b5c38b6648a404b1060..8ebbc4808c3509ff17ac3af045505dc42c003fb0 100644
> --- a/drivers/dax/dax-private.h
> +++ b/drivers/dax/dax-private.h
> +/**
> + * struct dax_resource - For sparse regions; an active resource
> + * @region: dax_region this resources is in
> + * @res: resource
> + * @use_cnt: count the number of uses of this resource
> + *
> + * Changes to the dax_reigon and the dax_resources within it are protected by
dax_region
> + * dax_region_rwsem
> + *
> + * dax_resource's are not intended to be used outside the dax layer.
> + */
> +struct dax_resource {
> + struct dax_region *region;
> + struct resource *res;
> + unsigned int use_cnt;
> +};
