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 13:44:38 +0200 Message-ID: <20190802114438.GH6461@dhcp22.suse.cz> References: <156431697805.3170.6377599347542228221.stgit@buzz> <20190729154952.GC21958@cmpxchg.org> <20190729185509.GI9330@dhcp22.suse.cz> <20190802094028.GG6461@dhcp22.suse.cz> <105a2f1f-de5c-7bac-3aa5-87bd1dbcaed9@yandex-team.ru> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <105a2f1f-de5c-7bac-3aa5-87bd1dbcaed9@yandex-team.ru> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Konstantin Khlebnikov Cc: Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Vladimir Davydov On Fri 02-08-19 13:01:07, Konstantin Khlebnikov wrote: > > > 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. Yes, but we already have to deal with for hard limit reclaim. Also I would like to see any actual data to back any more complex solution. We should definitely start simple. > 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); ups, this should be s@GFP_KERNEL@gfp_mask@ > > + } else { > > + current->memcg_nr_pages_over_high += batch; > > + set_notify_resume(current); > > + } > > break; > > } > > } while ((memcg = parent_mem_cgroup(memcg))); > > -- Michal Hocko SUSE Labs