On Mon 21-10-19 17:54:35, David Hildenbrand wrote: > On 21.10.19 17:47, Michal Hocko wrote: > > On Mon 21-10-19 17:39:36, David Hildenbrand wrote: > > > On 21.10.19 16:43, Michal Hocko wrote: > > [...] > > > > We still set PageReserved before onlining pages and that one should be > > > > good to go as well (memmap_init_zone). > > > > Thanks! > > > > > > memmap_init_zone() is called when onlining memory. There, set all pages to > > > reserved right now (on context == MEMMAP_HOTPLUG). We clear PG_reserved when > > > onlining a page to the buddy (e.g., generic_online_page). If we would online > > > a memory block with holes, we would want to keep all such pages > > > (!pfn_valid()) set to reserved. Also, there might be other side effects. > > > > Isn't it sufficient to have those pages in a poisoned state? They are > > not onlined so their state is basically undefined anyway. I do not see > > how PageReserved makes this any better. > > It is what people have been using for a long time. Memory hole -> > PG_reserved. The memmap is valid, but people want to tell "this here is > crap, don't look at it". The page is poisoned, right? If yes then setting the reserved bit doesn't make any sense. > > Also is the hole inside a hotplugable memory something we really have to > > care about. Has anybody actually seen a platform to require that? > > That's what I was asking. I can see "support" for this was added basically > right from the beginning. I'd say we rip that out and cleanup/simplify. I am > not aware of a platform that requires this. Especially, memory holes on > DIMMs (detected during boot) seem like an unlikely thing. The thing is that the hotplug development shows ad-hoc decisions throughout the code. It is even worse that it is hard to guess whether some hludges are a result of a careful design or ad-hoc trial and failure approach on setups that never were production. Building on top of that be preserving hacks is not going to improve the situation. So I am perfectly fine to focus on making the most straightforward setups work reliably. Even when there is a risk of breaking some odd setups. We can fix them up later but we would have at least a specific example and document it. -- Michal Hocko SUSE Labs
