On Fri, 23 Aug 2024 14:32:32 -0700 Fan Ni <nifan.cxl@xxxxxxxxx> wrote: > On Fri, Aug 16, 2024 at 09:44:26AM -0500, ira.weiny@xxxxxxxxx wrote: > > From: Navneet Singh <navneet.singh@xxxxxxxxx> > > > > A dynamic capacity device (DCD) sends events to signal the host for > > changes in the availability of Dynamic Capacity (DC) memory. These > > events contain extents describing a DPA range and meta data for memory > > to be added or removed. Events may be sent from the device at any time. > > > > Three types of events can be signaled, Add, Release, and Force Release. > > > > On add, the host may accept or reject the memory being offered. If no > > region exists, or the extent is invalid, the extent should be rejected. > > Add extent events may be grouped by a 'more' bit which indicates those > > extents should be processed as a group. > > > > On remove, the host can delay the response until the host is safely not > > using the memory. If no region exists the release can be sent > > immediately. The host may also release extents (or partial extents) at > > any time. Thus the 'more' bit grouping of release events is of less > > value and can be ignored in favor of sending multiple release capacity > > responses for groups of release events. > > > > Force removal is intended as a mechanism between the FM and the device > > and intended only when the host is unresponsive, out of sync, or > > otherwise broken. Purposely ignore force removal events. > > > > Regions are made up of one or more devices which may be surfacing memory > > to the host. Once all devices in a region have surfaced an extent the > > region can expose a corresponding extent for the user to consume. > > Without interleaving a device extent forms a 1:1 relationship with the > > region extent. Immediately surface a region extent upon getting a > > device extent. > > > > Per the specification the device is allowed to offer or remove extents > > at any time. However, anticipated use cases can expect extents to be > > offered, accepted, and removed in well defined chunks. > > > > Simplify extent tracking with the following restrictions. > > > > 1) Flag for removal any extent which overlaps a requested > > release range. > > 2) Refuse the offer of extents which overlap already accepted > > memory ranges. > > 3) Accept again a range which has already been accepted by the > > host. (It is likely the device has an error because it > > should already know that this range was accepted. But from > > the host point of view it is safe to acknowledge that > > acceptance again.) > > > > Management of the region extent devices must be synchronized with > > potential uses of the memory within the DAX layer. Create region extent > > devices as children of the cxl_dax_region device such that the DAX > > region driver can co-drive them and synchronize with the DAX layer. > > Synchronization and management is handled in a subsequent patch. > > > > Process DCD events and create region devices. > > > > 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 minor change inline. Hi Fan, Crop please. I scanned past it 3 times when scrolling without noticing what you'd actually commented on. > > +/* See CXL 3.0 8.2.9.2.1.5 */ > > Update the reference to reflect CXL 3.1. > > Fan >
