A quick followup, which may indicate a flaw in fs_dax page mapping code.
When doing that mapping of 32G, for each group of 8G, all but the last 2M resulted in a NOPAGE 2M fault. The very last 2M chunk of each 8G region resulted in FALLBACK. Then, a spawned thread accessed the same region sequentially, This caused the upper 16G all to result in FALLBACK (except those two 2M regions that already had done FALLBACK). The first case "smells" like some kind of range error in the code. The second one is also curiously regular, but I have less of a theory about it. Is this the right place for discussion of this behavior and possible patches? Regards - Eliot Moss
