On Wed, 24 Feb 2010, Miao Xie wrote: > >> Sorry, Could you explain what you advised? > >> I think it is hard to fix this problem by adding a variant, because it is > >> hard to avoid loading a word of the mask before > >> > >> nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems); > >> > >> and then loading another word of the mask after > >> > >> tsk->mems_allowed = *newmems; > >> > >> unless we use lock. > >> > >> Maybe we need a rw-lock to protect task->mems_allowed. > >> > > > > I meant that we need to define synchronization only for configurations > > that do not do atomic nodemask_t stores, it's otherwise unnecessary. > > We'll need to load and store tsk->mems_allowed via a helper function that > > is defined to take the rwlock for such configs and only read/write the > > nodemask for others. > > > > By investigating, we found that it is hard to guarantee the consistent between > mempolicy and mems_allowed because mempolicy was designed as a self-update function. > it just can be changed by one's self. Maybe we must change the implement of mempolicy. > Before your change, cpuset nodemask changes were serialized on manage_mutex which would, in turn, serialize the rebinding of each attached task's mempolicy. update_nodemask() is now serialized on cgroup_lock(), which also protects scan_for_empty_cpusets(), so the cpuset code protects it adequately. If a concurrent mempolicy change from a user's set_mempolicy() happens, however, it could introduce an inconsistency between them. If we protect current->mems_allowed with a rwlock or seqlock for configs where MAX_NUMNODES > BITS_PER_LONG, then we can always guarantee that we get the entire nodemask. The same problem is present for current->cpus_allowed, however, with NR_CPUS > BITS_PER_LONG. We must be able to safely dereference both masks without the chance of returning nodes_empty() or cpus_empty(). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>