From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936248AbdEWGuB (ORCPT ); Tue, 23 May 2017 02:50:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:33327 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933142AbdEWGt4 (ORCPT ); Tue, 23 May 2017 02:49:56 -0400 Date: Tue, 23 May 2017 08:49:44 +0200 From: Michal Hocko To: Mike Snitzer Cc: Mikulas Patocka , Junaid Shahid , David Rientjes , Alasdair Kergon , Andrew Morton , linux-mm@kvack.org, andreslc@google.com, gthelen@google.com, vbabka@suse.cz, linux-kernel@vger.kernel.org Subject: Re: dm ioctl: Restore __GFP_HIGH in copy_params() Message-ID: <20170523064944.GA12818@dhcp22.suse.cz> References: <1508444.i5EqlA1upv@js-desktop.svl.corp.google.com> <20170519074647.GC13041@dhcp22.suse.cz> <20170522093725.GF8509@dhcp22.suse.cz> <20170522120937.GI8509@dhcp22.suse.cz> <20170522150321.GM8509@dhcp22.suse.cz> <20170522180415.GA25340@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170522180415.GA25340@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 22-05-17 14:04:15, Mike Snitzer wrote: > On Mon, May 22 2017 at 11:03am -0400, > Michal Hocko wrote: > > > On Mon 22-05-17 10:52:44, Mikulas Patocka wrote: > > > > > > > > > On Mon, 22 May 2017, Michal Hocko wrote: > > [...] > > > > I am not sure I understand. OOM killer is invoked for _all_ allocations > > > > <= PAGE_ALLOC_COSTLY_ORDER that do not have __GFP_NORETRY as long as the > > > > OOM killer is not disabled (oom_killer_disable) and that only happens > > > > from the PM suspend path which makes sure that no userspace is active at > > > > the time. AFAIU this is a userspace triggered path and so the later > > > > shouldn't apply to it and GFP_KERNEL should be therefore sufficient. > > > > Relying to a portion of memory reserves to prevent from deadlock seems > > > > fundamentaly broken to me. > > > > > > > > > > The lvm2 was designed this way - it is broken, but there is not much that > > > can be done about it - fixing this would mean major rewrite. The only > > > thing we can do about it is to lower the deadlock probability with > > > __GFP_HIGH (or PF_MEMALLOC that was used some times ago). > > Yes, lvm2 was originally designed to to have access to memory reserves > to ensure forward progress. But if the mm subsystem has improved to > allow for the required progress without lvm2 trying to stake a claim on > those reserves then we'll gladly avoid (ab)using them. > > > But let me repeat. GFP_KERNEL allocation for order-0 page will not fail. > > OK, but will it be serviced immediately? Not failing isn't useful if it > never completes. Well, GFP_KERNEL will not guarantee an immediate success of course. There is nothing like that. Nor __GFP_HIGH will guarantee that, though, because reserves can get easily depleted by some workloads. You would have to use a dedicated memory pool to accomplish what you really need. -- Michal Hocko SUSE Labs