API+doxy: clarify that NUMA subtypes may be missing or wrong

Document HWLOC_MEMTIERS= envvar for overwriting them.

Signed-off-by: Brice Goglin <[email protected]>

Author: bgoglin

doc/hwloc.doxy

@@ -1947,6 +1947,10 @@ subtype <tt>DRAM</tt> (for usual main memory),
 <tt>MCDRAM</tt> (on KNL),
 <tt>GPUMemory</tt> (on POWER architecture with NVIDIA GPU memory shared over NVLink),
 <tt>CXL-DRAM</tt> or <tt>CXL-NVM</tt> for CXL DRAM or non-volatile memory.
+Note that some of these subtypes are guessed by the library,
+they might be missing or slightly wrong in some corner cases.
+See HWLOC_MEMTIERS and HWLOC_MEMTIERS_GUESS
+in \ref envvar for tuning these.
 </li>
 <li>Groups:
 subtype <tt>Cluster</tt>, <tt>Module</tt>, <tt>Tile</tt>, <tt>Compute Unit</tt>,

include/hwloc.h

@@ -263,6 +263,11 @@ typedef enum {
 			  * This is the smallest object representing Memory resources,
 			  * it cannot have any child except Misc objects.
 			  * However it may have Memory-side cache parents.
+                          *
+                          * NUMA nodes may correspond to different kinds of memory
+                          * (DRAM, HBM, CXL-DRAM, etc.). When hwloc is able to guess
+                          * that kind, it is specified in the subtype field of the object.
+                          * See also \ref attributes_normal in the main documentation.
 			  *
 			  * There is always at least one such object in the topology
 			  * even if the machine is not NUMA.