From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754062AbeDRN1i (ORCPT ); Wed, 18 Apr 2018 09:27:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:32823 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753442AbeDRN1R (ORCPT ); Wed, 18 Apr 2018 09:27:17 -0400 Date: Wed, 18 Apr 2018 15:27:15 +0200 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm , Johannes Weiner , Vladimir Davydov Subject: Re: [PATCH] mm:memcg: add __GFP_NOWARN in __memcg_schedule_kmem_cache_create Message-ID: <20180418132715.GD17484@dhcp22.suse.cz> References: <20180418022912.248417-1-minchan@kernel.org> <20180418072002.GN17484@dhcp22.suse.cz> <20180418074117.GA210164@rodete-desktop-imager.corp.google.com> <20180418075437.GP17484@dhcp22.suse.cz> <20180418132328.GB210164@rodete-desktop-imager.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180418132328.GB210164@rodete-desktop-imager.corp.google.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 18-04-18 22:23:28, Minchan Kim wrote: > On Wed, Apr 18, 2018 at 09:54:37AM +0200, Michal Hocko wrote: > > On Wed 18-04-18 16:41:17, Minchan Kim wrote: > > > On Wed, Apr 18, 2018 at 09:20:02AM +0200, Michal Hocko wrote: > > > > On Wed 18-04-18 11:29:12, Minchan Kim wrote: > > [...] > > > > > Let's not make user scared. > > > > > > > > This is not a proper explanation. So what exactly happens when this > > > > allocation fails? I would suggest something like the following > > > > " > > > > __memcg_schedule_kmem_cache_create tries to create a shadow slab cache > > > > and the worker allocation failure is not really critical because we will > > > > retry on the next kmem charge. We might miss some charges but that > > > > shouldn't be critical. The excessive allocation failure report is not > > > > very much helpful. Replace it with a rate limited single line output so > > > > that we know that there is a lot of these failures and that we need to > > > > do something about it in future. > > > > " > > > > > > > > With the last part to be implemented of course. > > > > > > If you want to see warning and catch on it in future, I don't see any reason > > > to change it. Because I didn't see any excessive warning output that it could > > > make system slow unless we did ratelimiting. > > > > Yeah, but a single line would be as much informative and less scary to > > users. > > > > > It was a just report from non-MM guys who have a concern that somethings > > > might go wrong on the system. I just wanted them relax since it's not > > > critical. > > > > I do agree with __GFP_NOWARN but I think a single line warning is due > > and helpful for further debugging. > > Okay, no problem. However, I don't feel we need ratelimit at this moment. > We can do when we got real report. Let's add just one line warning. > However, I have no talent to write a poem to express with one line. > Could you help me? What about pr_info("Failed to create memcg slab cache. Report if you see floods of these\n"); > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 671d07e73a3b..e26f85cac63f 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2201,8 +2201,11 @@ static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg, > struct memcg_kmem_cache_create_work *cw; > > cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN); > - if (!cw) > + if (!cw) { > + pr_warn("Fail to create shadow slab cache for memcg but it's not critical.\n"); > + pr_warn("If you see lots of this message, send an email to linux-mm@kvack.org\n"); > return; > + } > > css_get(&memcg->css); -- Michal Hocko SUSE Labs