On Tue, 7 Jan 2025 14:42:16 +1100 Alistair Popple <apopple@xxxxxxxxxx> wrote: > Device and 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. > > By treating the refcounts on these pages the same way as normal pages > we can remove a lot of special checks. In particular pXd_trans_huge() > becomes the same as pXd_leaf(), although I haven't made that change > here. It also frees up a valuable SW define PTE bit on architectures > that have devmap PTE bits defined. > > It also almost certainly allows further clean-up of the devmap managed > functions, but I have left that as a future improvment. It also > enables support for compound ZONE_DEVICE pages which is one of my > primary motivators for doing this work. > https://lkml.kernel.org/r/wysuus23bqmjtwkfu3zutqtmkse3ki3erf45x32yezlrl24qto@xlqt7qducyld made me expect merge/build/runtime issues, however this series merges and builds OK on mm-unstable. Did something change? What's the story here? Oh well, it built so I'll ship it!
