On Tue 17-01-23 17:19:46, Suren Baghdasaryan wrote: > On Tue, Jan 17, 2023 at 7:57 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Mon 09-01-23 12:53:34, Suren Baghdasaryan wrote: > > > call_rcu() can take a long time when callback offloading is enabled. > > > Its use in the vm_area_free can cause regressions in the exit path when > > > multiple VMAs are being freed. > > > > What kind of regressions. > > > > > To minimize that impact, place VMAs into > > > a list and free them in groups using one call_rcu() call per group. > > > > Please add some data to justify this additional complexity. > > Sorry, should have done that in the first place. A 4.3% regression was > noticed when running execl test from unixbench suite. spawn test also > showed 1.6% regression. Profiling revealed that vma freeing was taking > longer due to call_rcu() which is slow when RCU callback offloading is > enabled. Could you be more specific? vma freeing is async with the RCU so how come this has resulted in a regression? Is there any heavy rcu_synchronize in the exec path? That would be an interesting information. -- Michal Hocko SUSE Labs
