Messages in this thread | | | Subject | Re: [PATCH RFC] mm/memcontrol: reclaim severe usage over high limit in get_user_pages loop | From | Konstantin Khlebnikov <> | Date | Fri, 2 Aug 2019 13:01:07 +0300 |
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On 02.08.2019 12:40, Michal Hocko wrote: > On Mon 29-07-19 20:55:09, Michal Hocko wrote: >> On Mon 29-07-19 11:49:52, Johannes Weiner wrote: >>> On Sun, Jul 28, 2019 at 03:29:38PM +0300, Konstantin Khlebnikov wrote: >>>> --- a/mm/gup.c >>>> +++ b/mm/gup.c >>>> @@ -847,8 +847,11 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, >>>> ret = -ERESTARTSYS; >>>> goto out; >>>> } >>>> - cond_resched(); >>>> >>>> + /* Reclaim memory over high limit before stocking too much */ >>>> + mem_cgroup_handle_over_high(true); >>> >>> I'd rather this remained part of the try_charge() call. The code >>> comment in try_charge says this: >>> >>> * 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. >>> >>> The simplicity argument doesn't hold true anymore once we have to add >>> manual calls into allocation sites. We should instead fix try_charge() >>> to do synchronous reclaim for __GFP_RECLAIM and only punt to userspace >>> return when actually needed. >> >> Agreed. If we want to do direct reclaim on the high limit breach then it >> should go into try_charge same way we do hard limit reclaim there. I am >> not yet sure about how/whether to scale the excess. The only reason to >> move reclaim to return-to-userspace path was GFP_NOWAIT charges. As you >> say, maybe we should start by always performing the reclaim for >> sleepable contexts first and only defer for non-sleeping requests. > > In other words. Something like patch below (completely untested). Could > you give it a try Konstantin?
This should work but also eliminate all benefits from deferred reclaim: bigger batching and running without of any locks.
After that gap between high and max will work just as reserve for atomic allocations.
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index ba9138a4a1de..53a35c526e43 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2429,8 +2429,12 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > schedule_work(&memcg->high_work); > break; > } > - current->memcg_nr_pages_over_high += batch; > - set_notify_resume(current); > + if (gfpflags_allow_blocking(gfp_mask)) { > + reclaim_high(memcg, nr_pages, GFP_KERNEL); > + } else { > + current->memcg_nr_pages_over_high += batch; > + set_notify_resume(current); > + } > break; > } > } while ((memcg = parent_mem_cgroup(memcg))); >
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