On Thu 10-03-16 15:50:14, Johannes Weiner wrote: > Setting the original memory.limit_in_bytes hardlimit is subject to a > race condition when the desired value is below the current usage. The > code tries a few times to first reclaim and then see if the usage has > dropped to where we would like it to be, but there is no locking, and > the workload is free to continue making new charges up to the old > limit. Thus, attempting to shrink a workload relies on pure luck and > hope that the workload happens to cooperate.
OK this would be indeed a problem when you want to stop a runaway load. > To fix this in the cgroup2 memory.max knob, do it the other way round: > set the limit first, then try enforcement. And if reclaim is not able > to succeed, trigger OOM kills in the group. Keep going until the new > limit is met, we run out of OOM victims and there's only unreclaimable > memory left, or the task writing to memory.max is killed. This allows > users to shrink groups reliably, and the behavior is consistent with > what happens when new charges are attempted in excess of memory.max. Here as well. I think this should go into 4.5 final or later to stable so that we do not have different behavior of the knob. > Signed-off-by: Johannes Weiner <[email protected]> Acked-by: Michal Hocko <[email protected]> One nit below [...] > @@ -5037,9 +5040,36 @@ static ssize_t memory_max_write(struct > kernfs_open_file *of, > if (err) > return err; > > - err = mem_cgroup_resize_limit(memcg, max); > - if (err) > - return err; > + xchg(&memcg->memory.limit, max); > + > + for (;;) { > + unsigned long nr_pages = page_counter_read(&memcg->memory); > + > + if (nr_pages <= max) > + break; > + > + if (signal_pending(current)) { Didn't you want fatal_signal_pending here? At least the changelog suggests that. > + err = -EINTR; > + break; > + } -- Michal Hocko SUSE Labs
