On Tue, 05 Nov 2024 12:38:45 -0600 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. > > Speculative writes after a release may dirty the cache such that a read > from a newly surfaced extent may not come from the device. Call > cxl_region_invalidate_memregion() prior to bringing a new extent online > to ensure the cache is marked invalid. > > While these invalidate calls are inefficient they are the best we can do > to ensure cache consistency without back invalidate. Furthermore this > should occur infrequently with sufficiently large extents and work loads > to not be too bad of an impact. > > 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> Same again. Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
