On 7/19/19 2:20 AM, Michal Hocko wrote: > On Wed 17-07-19 16:24:12, Waiman Long wrote: >> Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink >> file to shrink the slab by flushing out all the per-cpu slabs and free >> slabs in partial lists. This can be useful to squeeze out a bit more memory >> under extreme condition as well as making the active object counts in >> /proc/slabinfo more accurate. >> >> This usually applies only to the root caches, as the SLUB_MEMCG_SYSFS_ON >> option is usually not enabled and "slub_memcg_sysfs=1" not set. Even >> if memcg sysfs is turned on, it is too cumbersome and impractical to >> manage all those per-memcg sysfs files in a real production system. >> >> So there is no practical way to shrink memcg caches. Fix this by >> enabling a proper write to the shrink sysfs file of the root cache >> to scan all the available memcg caches and shrink them as well. For a >> non-root memcg cache (when SLUB_MEMCG_SYSFS_ON or slub_memcg_sysfs is >> on), only that cache will be shrunk when written. > I would mention that memcg unawareness was an overlook more than > anything else. The interface is intended to shrink all pcp data of the > cache. The fact that we are using per-memcg internal caches is an > implementation detail. > >> On a 2-socket 64-core 256-thread arm64 system with 64k page after >> a parallel kernel build, the the amount of memory occupied by slabs >> before shrinking slabs were: >> >> # grep task_struct /proc/slabinfo >> task_struct 53137 53192 4288 61 4 : tunables 0 0 >> 0 : slabdata 872 872 0 >> # grep "^S[lRU]" /proc/meminfo >> Slab: 3936832 kB >> SReclaimable: 399104 kB >> SUnreclaim: 3537728 kB >> >> After shrinking slabs: >> >> # grep "^S[lRU]" /proc/meminfo >> Slab: 1356288 kB >> SReclaimable: 263296 kB >> SUnreclaim: 1092992 kB >> # grep task_struct /proc/slabinfo >> task_struct 2764 6832 4288 61 4 : tunables 0 0 >> 0 : slabdata 112 112 0 > Now that you are touching the documentation I would just add a note that > shrinking might be expensive and block other slab operations so it > should be used with some care. > Good point. I will update the patch to include such a note in the documentation. Thanks, Longman
