On Thu, 26 Jul 2018 10:45:54 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote: > > Does each user of PG_balloon check for PG_reserved? If this is the case > > then yes this would be OK. > > > > I can only spot one user of PageBalloon() at all (fs/proc/page.c) , > which makes me wonder if this bit is actually still relevant. I think > the last "real" user was removed with > > commit b1123ea6d3b3da25af5c8a9d843bd07ab63213f4 > Author: Minchan Kim <minchan@xxxxxxxxxx> > Date: Tue Jul 26 15:23:09 2016 -0700 > > mm: balloon: use general non-lru movable page feature > > Now, VM has a feature to migrate non-lru movable pages so balloon > doesn't need custom migration hooks in migrate.c and compaction.c. > > > The only user of PG_balloon in general is > "include/linux/balloon_compaction.h", used effectively only by > virtio_balloon. > > All such pages are allocated via balloon_page_alloc() and never set > reserved. > > So to me it looks like PG_balloon could be easily reused, especially to > also exclude virtio-balloon pages from dumps. Agree. Maintaining a thingy for page-types.c which hardly anyone uses (surely) isn't sufficient justification for consuming a page flag. We should check with the virtio developers first, but this does seem to be begging to be reclaimed.
