linux-kernel - Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers

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Date:   Mon, 25 Jun 2018 10:01:03 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Felix Kuehling <felix.kuehling@....com>
Cc:     Christian König <christian.koenig@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Sudeep Dutt <sudeep.dutt@...el.com>,
        Ashutosh Dixit <ashutosh.dixit@...el.com>,
        Dimitri Sivanich <sivanich@....com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>, kvm@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        xen-devel@...ts.xenproject.org, linux-mm@...ck.org,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers

On Fri 22-06-18 16:09:06, Felix Kuehling wrote:
> On 2018-06-22 11:24 AM, Michal Hocko wrote:
> > On Fri 22-06-18 17:13:02, Christian König wrote:
> >> Hi Michal,
> >>
> >> [Adding Felix as well]
> >>
> >> Well first of all you have a misconception why at least the AMD graphics
> >> driver need to be able to sleep in an MMU notifier: We need to sleep because
> >> we need to wait for hardware operations to finish and *NOT* because we need
> >> to wait for locks.
> >>
> >> I'm not sure if your flag now means that you generally can't sleep in MMU
> >> notifiers any more, but if that's the case at least AMD hardware will break
> >> badly. In our case the approach of waiting for a short time for the process
> >> to be reaped and then select another victim actually sounds like the right
> >> thing to do.
> > Well, I do not need to make the notifier code non blocking all the time.
> > All I need is to ensure that it won't sleep if the flag says so and
> > return -EAGAIN instead.
> >
> > So here is what I do for amdgpu:
> 
> In the case of KFD we also need to take the DQM lock:
> 
> amdgpu_mn_invalidate_range_start_hsa -> amdgpu_amdkfd_evict_userptr ->
> kgd2kfd_quiesce_mm -> kfd_process_evict_queues -> evict_process_queues_cpsch
> 
> So we'd need to pass the blockable parameter all the way through that
> call chain.

Thanks, I have missed that part. So I guess I will start with something
similar to intel-gfx and back off when the current range needs some
treatment. So this on top. Does it look correct?

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
index d138a526feff..e2d422b3eb0b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
@@ -266,6 +266,11 @@ static int amdgpu_mn_invalidate_range_start_hsa(struct mmu_notifier *mn,
 		struct amdgpu_mn_node *node;
 		struct amdgpu_bo *bo;
 
+		if (!blockable) {
+			amdgpu_mn_read_unlock();
+			return -EAGAIN;
+		}
+
 		node = container_of(it, struct amdgpu_mn_node, it);
 		it = interval_tree_iter_next(it, start, end);
 
-- 
Michal Hocko
SUSE Labs