On 09.09.20 13:27, osalvador@xxxxxxx wrote: > On 2020-09-09 12:54, Vlastimil Babka wrote: >> Thanks! I expect no performance change while no isolation is in >> progress, as >> there are no new tests added in alloc/free paths. During page isolation >> there's >> a single drain instead of once-per-pageblock, which is a benefit. But >> the >> pcplists are effectively disabled for the whole of online_pages(), >> offline_pages() or alloc_contig_range(), which will affect parallel >> page >> allocator users. It depends on how long these operations take and how >> heavy the >> parallel usage is, so I have no good answers. Might be similar to the >> current >> periodic drain. > > I have seen some systems taking quite some time when offlining sections > due to the migration of > the respective pages not being that smooth and having do_migrate_range > to do some spins. > But to be fair, online_pages and offline_pages are not routines that get > called that often, and we would be safe to assume that memory-hotplug > operations are not constantly happening, but are rather one-offs > operations. > > I am not sure about Xen and HV, IIRC Xen was using online_pages and > offline_pages routines to do the ballooning? No, they only add more memory blocks and online them. Memory hot(un)plug is an expensive operation already, I don't think that's an issue. -- Thanks, David / dhildenb
