Jason Gunthorpe wrote: > On Thu, Apr 11, 2024 at 10:28:56AM -0700, Dan Williams wrote: > > Alistair Popple wrote: > > > FS DAX pages have always maintained their own page reference counts > > > without following the normal rules for page reference counting. In > > > particular pages are considered free when the refcount hits one rather > > > than zero and refcounts are not added when mapping the page. > > > > > Tracking this requires special PTE bits (PTE_DEVMAP) and a secondary > > > mechanism for allowing GUP to hold references on the page (see > > > get_dev_pagemap). However there doesn't seem to be any reason why FS > > > DAX pages need their own reference counting scheme. > > > > This is fair. However, for anyone coming in fresh to this situation > > maybe some more "how we get here" history helps. That longer story is > > here: > > > > http://lore.kernel.org/all/166579181584.2236710.17813547487183983273.stgit@xxxxxxxxxxxxxxxxxxxxxxxxx/ > > This never got merged? :( Yeah... I got hung up on the "allocation" API to take ZONE_DEVICE pages from recfount 0 to 1 and then never circled back.
