On Wed 08-08-18 16:20:54, Kirill Tkhai wrote: > [Added two more places needed srcu_dereference(). All ->shrinker_map > dereferences must be under SRCU, and this v2 adds missed in previous] > > The patch makes shrinker list and shrinker_idr SRCU-safe > for readers. This requires synchronize_srcu() on finalize > stage unregistering stage, which waits till all parallel > shrink_slab() are finished > > Note, that patch removes rwsem_is_contended() checks from > the code, and this does not result in delays during > registration, since there is no waiting at all. Unregistration > case may be optimized by splitting unregister_shrinker() > in tho stages, and this is made in next patches. > > Also, keep in mind, that in case of SRCU is not allowed > to make unconditional (which is done in previous patch), > it is possible to use percpu_rw_semaphore instead of it. > percpu_down_read() will be used in shrink_slab_memcg() > and in shrink_slab(), and consecutive calls > > percpu_down_write(percpu_rwsem); > percpu_up_write(percpu_rwsem); > > will be used instead of synchronize_srcu(). An obvious question. Why didn't you go that way? What are pros/cons of both approaches? -- Michal Hocko SUSE Labs
