On Wed 02-01-19 17:56:38, Shakeel Butt wrote: > If a memcg is over high limit, memory reclaim is scheduled to run on > return-to-userland. However it is assumed that the memcg is the current > process's memcg. With remote memcg charging for kmem or swapping in a > page charged to remote memcg, current process can trigger reclaim on > remote memcg. So, schduling reclaim on return-to-userland for remote > memcgs will ignore the high reclaim altogether. So, punt the high > reclaim of remote memcgs to high_work.
Have you seen this happening in real life workloads? And is this offloading what we really want to do? I mean it is clearly the current task that has triggered the remote charge so why should we offload that work to a system? Is there any reason we cannot reclaim on the remote memcg from the return-to-userland path? > Signed-off-by: Shakeel Butt <[email protected]> > --- > mm/memcontrol.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e9db1160ccbc..47439c84667a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2302,19 +2302,23 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t > gfp_mask, > * reclaim on returning to userland. We can perform reclaim here > * if __GFP_RECLAIM but let's always punt for simplicity and so that > * GFP_KERNEL can consistently be used during reclaim. @memcg is > - * not recorded as it most likely matches current's and won't > - * change in the meantime. As high limit is checked again before > - * reclaim, the cost of mismatch is negligible. > + * not recorded as the return-to-userland high reclaim will only reclaim > + * from current's memcg (or its ancestor). For other memcgs we punt them > + * to work queue. > */ > do { > if (page_counter_read(&memcg->memory) > memcg->high) { > - /* Don't bother a random interrupted task */ > - if (in_interrupt()) { > + /* > + * Don't bother a random interrupted task or if the > + * memcg is not current's memcg's ancestor. > + */ > + if (in_interrupt() || > + !mm_match_cgroup(current->mm, memcg)) { > schedule_work(&memcg->high_work); > - break; > + } else { > + current->memcg_nr_pages_over_high += batch; > + set_notify_resume(current); > } > - current->memcg_nr_pages_over_high += batch; > - set_notify_resume(current); > break; > } > } while ((memcg = parent_mem_cgroup(memcg))); > -- > 2.20.1.415.g653613c723-goog > -- Michal Hocko SUSE Labs
