On Wed 10-10-18 09:39:08, Alexander Duyck wrote: > On 10/10/2018 2:58 AM, Michal Hocko wrote: > > On Tue 09-10-18 13:26:41, Alexander Duyck wrote: > > [...] > > > I would think with that being the case we still probably need the call to > > > __SetPageReserved to set the bit with the expectation that it will not be > > > cleared for device-pages since the pages are not onlined. Removing the call > > > to __SetPageReserved would probably introduce a number of regressions as > > > there are multiple spots that use the reserved bit to determine if a page > > > can be swapped out to disk, mapped as system memory, or migrated. > > > > PageReserved is meant to tell any potential pfn walkers that might get > > to this struct page to back off and not touch it. Even though > > ZONE_DEVICE doesn't online pages in traditional sense it makes those > > pages available for further use so the page reserved bit should be > > cleared. > > So from what I can tell that isn't necessarily the case. Specifically if the > pagemap type is MEMORY_DEVICE_PRIVATE or MEMORY_DEVICE_PUBLIC both are > special cases where the memory may not be accessible to the CPU or cannot be > pinned in order to allow for eviction. Could you give me an example please? > The specific case that Dan and Yi are referring to is for the type > MEMORY_DEVICE_FS_DAX. For that type I could probably look at not setting the > reserved bit. Part of me wants to say that we should wait and clear the bit > later, but that would end up just adding time back to initialization. At > this point I would consider the change more of a follow-up optimization > rather than a fix though since this is tailoring things specifically for DAX > versus the other ZONE_DEVICE types. I thought I have already made it clear that these zone device hacks are not acceptable to the generic hotplug code. If the current reserve bit handling is not correct then give us a specific reason for that and we can start thinking about the proper fix. -- Michal Hocko SUSE Labs
