On Mon 29-07-19 17:20:52, Minchan Kim wrote: > On Mon, Jul 29, 2019 at 09:45:23AM +0200, Michal Hocko wrote: > > On Mon 29-07-19 16:10:37, Minchan Kim wrote: > > > In our testing(carmera recording), Miguel and Wei found unmap_page_range > > > takes above 6ms with preemption disabled easily. When I see that, the > > > reason is it holds page table spinlock during entire 512 page operation > > > in a PMD. 6.2ms is never trivial for user experince if RT task couldn't > > > run in the time because it could make frame drop or glitch audio problem. > > > > Where is the time spent during the tear down? 512 pages doesn't sound > > like a lot to tear down. Is it the TLB flushing? > > Miguel confirmed there is no such big latency without mark_page_accessed > in zap_pte_range so I guess it's the contention of LRU lock as well as > heavy activate_page overhead which is not trivial, either.
Please give us more details ideally with some numbers. -- Michal Hocko SUSE Labs
