On Fri, May 22, 2015 at 06:23:18PM -0400, Tejun Heo wrote: > cpu_possible_mask represents the CPUs which are actually possible > during that boot instance. For systems which don't support CPU > hotplug, this will match cpu_online_mask exactly in most cases. Even > for systems which support CPU hotplug, the number of possible CPU > slots is highly unlikely to diverge greatly from the number of online > CPUs. The only cases where the difference between possible and online > caused problems were when the boot code failed to initialize the > possible mask and left it fully set at NR_CPUS - 1. > > As such, most per-cpu constructs allocate for all possible CPUs and > often iterate over the possibles, which also has the benefit of > avoiding the blocking CPU hotplug synchronization. > > memcg open codes per-cpu stat counting for mem_cgroup_read_stat() and > mem_cgroup_read_events(), which iterates over online CPUs and handles > CPU hotplug operations explicitly. This complexity doesn't actually > buy anything. Switch to iterating over the possibles and drop the > explicit CPU hotplug handling. > > Eventually, we want to convert memcg to use percpu_counter instead of > its own custom implementation which also benefits from quick access > w/o summing for cases where larger error margin is acceptable. > > This will allow mem_cgroup_read_stat() to be called from non-sleepable > contexts which will be used by cgroup writeback. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
