On Thu 26-07-18 10:22:41, David Hildenbrand wrote: > On 24.07.2018 09:22, Michal Hocko wrote: > > On Mon 23-07-18 19:12:58, David Hildenbrand wrote: > >> On 23.07.2018 13:45, Vlastimil Babka wrote: > >>> On 07/20/2018 02:34 PM, David Hildenbrand wrote: > >>>> Dumping tools (like makedumpfile) right now don't exclude reserved pages. > >>>> So reserved pages might be access by dump tools although nobody except > >>>> the owner should touch them. > >>> > >>> Are you sure about that? Or maybe I understand wrong. Maybe it changed > >>> recently, but IIRC pages that are backing memmap (struct pages) are also > >>> PG_reserved. And you definitely do want those in the dump. > >> > >> I proposed a new flag/value to mask pages that are logically offline but > >> Michal wanted me to go into this direction. > >> > >> While we can special case struct pages in dump tools ("we have to > >> read/interpret them either way, so we can also dump them"), it smells > >> like my original attempt was cleaner. Michal? > > > > But we do not have many page flags spare and even if we have one or two > > this doesn't look like the use for them. So I still think we should try > > the PageReserved way. > > > > So as a summary, the only real approach that would be acceptable is > using PageReserved + some other identifier to mark pages as "logically > offline". > > I wonder what identifier could be used, as this has to be consistent for > all reserved pages (to avoid false positives). > > Using other pageflags in combination might be possible, but then we have > to make assumptions about all users of PageReserved right now. > > As far as I can see (and as has been discussed), page_type could be > used. If we don't want to consume a new bit, we could overload/reuse the > "PG_balloon" bit. > > > E.g. "PG_balloon" set -> exclude page from dump
Does each user of PG_balloon check for PG_reserved? If this is the case then yes this would be OK. -- Michal Hocko SUSE Labs