From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id AFE8A6B2FE4 for ; Fri, 24 Aug 2018 09:53:00 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id k16-v6so744679ede.6 for ; Fri, 24 Aug 2018 06:53:00 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p43-v6si484233eda.158.2018.08.24.06.52.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 24 Aug 2018 06:52:59 -0700 (PDT) Date: Fri, 24 Aug 2018 15:52:57 +0200 From: Michal Hocko Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers Message-ID: <20180824135257.GU29735@dhcp22.suse.cz> References: <20180824120339.GL29735@dhcp22.suse.cz> <20180824123341.GN29735@dhcp22.suse.cz> <20180824130132.GP29735@dhcp22.suse.cz> <23d071d2-82e4-9b78-1000-be44db5f6523@gmail.com> <20180824132442.GQ29735@dhcp22.suse.cz> <86bd94d5-0ce8-c67f-07a5-ca9ebf399cdd@gmail.com> <20180824134009.GS29735@dhcp22.suse.cz> <735b0a53-5237-8827-d20e-e57fa24d798f@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <735b0a53-5237-8827-d20e-e57fa24d798f@amd.com> Sender: owner-linux-mm@kvack.org List-ID: To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: kvm@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , Tetsuo Handa , Sudeep Dutt , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Andrea Arcangeli , Dimitri Sivanich , Jason Gunthorpe , linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org, David Airlie , Doug Ledford , David Rientjes , xen-devel@lists.xenproject.org, intel-gfx@lists.freedesktop.org, Leon Romanovsky , =?iso-8859-1?B?Suly9G1l?= Glisse , Rodrigo Vivi , Boris Ostrovsky , Juergen Gross , Mike Marciniszyn , Dennis Dalessandro , LKML , Ashutosh Dixit , Alex Deucher , Paolo Bonzini , Andrew Morton , Felix Kuehling On Fri 24-08-18 15:44:03, Christian Konig wrote: > Am 24.08.2018 um 15:40 schrieb Michal Hocko: > > On Fri 24-08-18 15:28:33, Christian Konig wrote: > > > Am 24.08.2018 um 15:24 schrieb Michal Hocko: > > > > On Fri 24-08-18 15:10:08, Christian Konig wrote: > > > > > Am 24.08.2018 um 15:01 schrieb Michal Hocko: > > > > > > On Fri 24-08-18 14:52:26, Christian Konig wrote: > > > > > > > Am 24.08.2018 um 14:33 schrieb Michal Hocko: > > > > > > [...] > > > > > > > > Thiking about it some more, I can imagine that a notifier callback which > > > > > > > > performs an allocation might trigger a memory reclaim and that in turn > > > > > > > > might trigger a notifier to be invoked and recurse. But notifier > > > > > > > > shouldn't really allocate memory. They are called from deep MM code > > > > > > > > paths and this would be extremely deadlock prone. Maybe Jerome can come > > > > > > > > up some more realistic scenario. If not then I would propose to simplify > > > > > > > > the locking here. We have lockdep to catch self deadlocks and it is > > > > > > > > always better to handle a specific issue rather than having a code > > > > > > > > without a clear indication how it can recurse. > > > > > > > Well I agree that we should probably fix that, but I have some concerns to > > > > > > > remove the existing workaround. > > > > > > > > > > > > > > See we added that to get rid of a real problem in a customer environment and > > > > > > > I don't want to that to show up again. > > > > > > It would really help to know more about that case and fix it properly > > > > > > rather than workaround it like this. Anyway, let me think how to handle > > > > > > the non-blocking notifier invocation then. I was not able to come up > > > > > > with anything remotely sane yet. > > > > > With avoiding allocating memory in the write lock path I don't see an issue > > > > > any more with that. > > > > > > > > > > All what the write lock path does now is adding items to a linked lists, > > > > > arrays etc.... > > > > Can we change it to non-sleepable lock then? > > > No, the write side doesn't sleep any more, but the read side does. > > > > > > See amdgpu_mn_invalidate_node() and that is where you actually need to > > > handle the non-blocking flag correctly. > > Ohh, right you are. We already handle that by bailing out before calling > > amdgpu_mn_invalidate_node in !blockable mode. > > Yeah, that is sufficient. > > It could be improved because we have something like 90% chance that > amdgpu_mn_invalidate_node() actually doesn't need to do anything. > > But I can take care of that when the patch set has landed. > > > So does this looks good to you? > > Yeah, that looks perfect to me. Reviewed-by: Christian Konig > Cool! Thanks for your guidance and patience with me. Here is the full patch. Feel free to take it and route per your preference.