On Sun 28-07-19 15:29:38, Konstantin Khlebnikov wrote: > High memory limit in memory cgroup allows to batch memory reclaiming and > defer it until returning into userland. This moves it out of any locks. > > Fixed gap between high and max limit works pretty well (we are using > 64 * NR_CPUS pages) except cases when one syscall allocates tons of > memory. This affects all other tasks in cgroup because they might hit > max memory limit in unhandy places and\or under hot locks. > > For example mmap with MAP_POPULATE or MAP_LOCKED might allocate a lot > of pages and push memory cgroup usage far ahead high memory limit. > > This patch uses halfway between high and max limits as threshold and > in this case starts memory reclaiming if mem_cgroup_handle_over_high() > called with argument only_severe = true, otherwise reclaim is deferred > till returning into userland. If high limits isn't set nothing changes. > > Now long running get_user_pages will periodically reclaim cgroup memory. > Other possible targets are generic file read/write iter loops. I do see how gup can lead to a large high limit excess, but could you be more specific why is that a problem? We should be reclaiming the similar number of pages cumulatively. -- Michal Hocko SUSE Labs
