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: Mon, 29 Jul 2019 20:55:09 +0200 Message-ID: <20190729185509.GI9330@dhcp22.suse.cz> References: <156431697805.3170.6377599347542228221.stgit@buzz> <20190729154952.GC21958@cmpxchg.org> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20190729154952.GC21958@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Konstantin Khlebnikov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Vladimir Davydov 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. -- Michal Hocko SUSE Labs