From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH RFC] mm/memcontrol: reclaim severe usage over high limit in get_user_pages loop Date: Fri, 2 Aug 2019 11:40:28 +0200 Message-ID: <20190802094028.GG6461@dhcp22.suse.cz> References: <156431697805.3170.6377599347542228221.stgit@buzz> <20190729154952.GC21958@cmpxchg.org> <20190729185509.GI9330@dhcp22.suse.cz> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20190729185509.GI9330@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner , Konstantin Khlebnikov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Vladimir Davydov 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? 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))); -- Michal Hocko SUSE Labs