On Thu 27-06-19 17:16:04, Waiman Long wrote: > On 6/27/19 11:15 AM, Michal Hocko wrote: > > On Mon 24-06-19 13:42:19, Waiman Long wrote: > >> With the slub memory allocator, the numbers of active slab objects > >> reported in /proc/slabinfo are not real because they include objects > >> that are held by the per-cpu slab structures whether they are actually > >> used or not. The problem gets worse the more CPUs a system have. For > >> instance, looking at the reported number of active task_struct objects, > >> one will wonder where all the missing tasks gone. > >> > >> I know it is hard and costly to get a real count of active objects. > > What exactly is expensive? Why cannot slabinfo reduce the number of > > active objects by per-cpu cached objects? > > > The number of cachelines that needs to be accessed in order to get an > accurate count will be much higher if we need to iterate through all the > per-cpu structures. In addition, accessing the per-cpu partial list will > be racy. Why is all that a problem for a root only interface that should be used quite rarely (it is not something that you should be reading hundreds time per second, right)? -- Michal Hocko SUSE Labs
