On 6/28/19 3:31 AM, Michal Hocko wrote: > 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)? That can be true. Anyway, I have posted a new patch to use the existing <slab>/shrink sysfs file to perform memcg cache shrinking as well. So I am not going to pursue this patch. Thanks, Longman
