I've been going through the MDS cache objects moving referenced containers into the mempools to improve accuracy of cache size. This is being tracked in: http://tracker.ceph.com/issues/21402 One issue I've found is that any method which takes a container argument needs special handling when the container we sometimes pass is part of the mempool. For example, CDir::_committed [2] will need to copy the contents of the lists referenced in CDir::waiting_for_commit [3] in order to call MDSRank::queue_waiters [1]. This is because the types will no longer match: CDir.h: mempool::mds_co::compact_map<version_t, mempool::mds_co::list<MDSInternalContextBase*> > waiting_for_commit; (the list values would be passed to queue_waiters:) versus: MDSRank.h: void queue_waiters(list<MDSInternalContextBase*>& ls) Namely, we have std::list<MDSInternalContextBase*> and mempool::mds_co::list<MDSInternalContextBase*> aka std::list<MDSInternalContextBase*, mempool::mds_co::pool_allocator<MDSInternalContextBase*>> Apparently the new way to work around this problem where the templated allocator does not match is to embed the allocator in the object. This is done using the std::memory_resource [4] in C++17. So instead of: void queue_waiters(list<MDSInternalContextBase*>& ls) we would have: void queue_waiters(std::pmr::list<MDSInternalContextBase*>& ls) All of the callers of MDSRank::queue_waiters would also need updated to use either std::pmr::list or the MDSCacheObject's mempool::mds_co::list. Does anyone have any plans or opinions on using this with our mempool infrastructure? My understanding is that this is still experimental with the latest gcc, so this isn't something to be done today but may we should develop code with this in mind. [1] https://github.com/ceph/ceph/blob/aab2defacae9e0885e08b399f15b20c495b59d99/src/mds/MDSRank.h#L287 [2] https://github.com/ceph/ceph/blob/aab2defacae9e0885e08b399f15b20c495b59d99/src/mds/CDir.cc#L2407 [3] https://github.com/ceph/ceph/blob/aab2defacae9e0885e08b399f15b20c495b59d99/src/mds/CDir.h#L632 [4] http://en.cppreference.com/w/cpp/memory/memory_resource -- Patrick Donnelly -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
