From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [RFC PATCH] mm,
 oom: distinguish blockable mode for mmu notifiers
Date: Mon, 2 Jul 2018 14:20:03 +0200
Message-ID: <20180702122003.GN19043@dhcp22.suse.cz>
References: <20180622150242.16558-1-mhocko@kernel.org>
 <20180627074421.GF32348@dhcp22.suse.cz>
 <71f4184c-21ea-5af1-eeb6-bf7787614e2d@amd.com>
 <20180702115423.GK19043@dhcp22.suse.cz>
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To: Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc: kvm@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>, David Airlie <airlied@linux.ie>, Sudeep Dutt <sudeep.dutt@intel.com>, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Andrea Arcangeli <aarcange@redhat.com>, "David (ChunMing) Zhou" <David1.Zhou@amd.com>, Dimitri Sivanich <sivanich@sgi.com>, linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org, Jason Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>, David Rientjes <rientjes@google.com>, xen-devel@lists.xenproject.org, intel-gfx@lists.freedesktop.org, =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, Mike Marciniszyn <mike.marciniszyn@intel.com>, Dennis Dalessandro <dennis.dalessandro@intel.com>, LKML <linux-kernel@vger.kernel.org>, Ashutosh Dixit <ashut>
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Date:   Mon, 2 Jul 2018 14:20:03 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
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        Felix Kuehling <felix.kuehling@amd.com>
Subject: Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers
Message-ID: <20180702122003.GN19043@dhcp22.suse.cz>
References: <20180622150242.16558-1-mhocko@kernel.org>
 <20180627074421.GF32348@dhcp22.suse.cz>
 <71f4184c-21ea-5af1-eeb6-bf7787614e2d@amd.com>
 <20180702115423.GK19043@dhcp22.suse.cz>
 <725cb1ad-01b0-42b5-56f0-c08c29804cb4@amd.com>
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On Mon 02-07-18 14:13:42, Christian König wrote:
> Am 02.07.2018 um 13:54 schrieb Michal Hocko:
> > On Mon 02-07-18 11:14:58, Christian König wrote:
> > > Am 27.06.2018 um 09:44 schrieb Michal Hocko:
> > > > This is the v2 of RFC based on the feedback I've received so far. The
> > > > code even compiles as a bonus ;) I haven't runtime tested it yet, mostly
> > > > because I have no idea how.
> > > > 
> > > > Any further feedback is highly appreciated of course.
> > > That sounds like it should work and at least the amdgpu changes now look
> > > good to me on first glance.
> > > 
> > > Can you split that up further in the usual way? E.g. adding the blockable
> > > flag in one patch and fixing all implementations of the MMU notifier in
> > > follow up patches.
> > But such a code would be broken, no? Ignoring the blockable state will
> > simply lead to lockups until the fixup parts get applied.
> 
> Well to still be bisect-able you only need to get the interface change in
> first with fixing the function signature of the implementations.

That would only work if those functions return -AGAIN unconditionally.
Otherwise they would pretend to not block while that would be obviously
incorrect. This doesn't sound correct to me.

> Then add all the new code to the implementations and last start to actually
> use the new interface.
> 
> That is a pattern we use regularly and I think it's good practice to do
> this.

But we do rely on the proper blockable handling.

> > Is the split up really worth it? I was thinking about that but had hard
> > times to end up with something that would be bisectable. Well, except
> > for returning -EBUSY until all notifiers are implemented. Which I found
> > confusing.
> 
> It at least makes reviewing changes much easier, cause as driver maintainer
> I can concentrate on the stuff only related to me.
> 
> Additional to that when you cause some unrelated side effect in a driver we
> can much easier pinpoint the actual change later on when the patch is
> smaller.
> 
> > 
> > > This way I'm pretty sure Felix and I can give an rb on the amdgpu/amdkfd
> > > changes.
> > If you are worried to give r-b only for those then this can be done even
> > for larger patches. Just make your Reviewd-by more specific
> > R-b: name # For BLA BLA
> 
> Yeah, possible alternative but more work for me when I review it :)

I definitely do not want to add more work to reviewers and I completely
see how massive "flag days" like these are not popular but I really
didn't find a reasonable way around that would be both correct and
wouldn't add much more churn on the way. So if you really insist then I
would really appreciate a hint on the way to achive the same without any
above downsides.
-- 
Michal Hocko
SUSE Labs

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Date: Mon, 2 Jul 2018 14:20:03 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [RFC PATCH] mm, oom: distinguish blockable mode for mmu notifiers
Message-ID: <20180702122003.GN19043@dhcp22.suse.cz>
References: <20180622150242.16558-1-mhocko@kernel.org>
 <20180627074421.GF32348@dhcp22.suse.cz>
 <71f4184c-21ea-5af1-eeb6-bf7787614e2d@amd.com>
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To: Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc: LKML <linux-kernel@vger.kernel.org>, "David (ChunMing) Zhou" <David1.Zhou@amd.com>, Paolo Bonzini <pbonzini@redhat.com>, Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>, Alex Deucher <alexander.deucher@amd.com>, David Airlie <airlied@linux.ie>, Jani Nikula <jani.nikula@linux.intel.com>, Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, Doug Ledford <dledford@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>, Mike Marciniszyn <mike.marciniszyn@intel.com>, Dennis Dalessandro <dennis.dalessandro@intel.com>, Sudeep Dutt <sudeep.dutt@intel.com>, Ashutosh Dixit <ashutosh.dixit@intel.com>, Dimitri Sivanich <sivanich@sgi.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>, kvm@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-rdma@vger.kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org, David Rientjes <rientjes@google.com>, Felix Kuehling <felix.kuehling@amd.com>

On Mon 02-07-18 14:13:42, Christian Konig wrote:
> Am 02.07.2018 um 13:54 schrieb Michal Hocko:
> > On Mon 02-07-18 11:14:58, Christian Konig wrote:
> > > Am 27.06.2018 um 09:44 schrieb Michal Hocko:
> > > > This is the v2 of RFC based on the feedback I've received so far. The
> > > > code even compiles as a bonus ;) I haven't runtime tested it yet, mostly
> > > > because I have no idea how.
> > > > 
> > > > Any further feedback is highly appreciated of course.
> > > That sounds like it should work and at least the amdgpu changes now look
> > > good to me on first glance.
> > > 
> > > Can you split that up further in the usual way? E.g. adding the blockable
> > > flag in one patch and fixing all implementations of the MMU notifier in
> > > follow up patches.
> > But such a code would be broken, no? Ignoring the blockable state will
> > simply lead to lockups until the fixup parts get applied.
> 
> Well to still be bisect-able you only need to get the interface change in
> first with fixing the function signature of the implementations.

That would only work if those functions return -AGAIN unconditionally.
Otherwise they would pretend to not block while that would be obviously
incorrect. This doesn't sound correct to me.

> Then add all the new code to the implementations and last start to actually
> use the new interface.
> 
> That is a pattern we use regularly and I think it's good practice to do
> this.

But we do rely on the proper blockable handling.

> > Is the split up really worth it? I was thinking about that but had hard
> > times to end up with something that would be bisectable. Well, except
> > for returning -EBUSY until all notifiers are implemented. Which I found
> > confusing.
> 
> It at least makes reviewing changes much easier, cause as driver maintainer
> I can concentrate on the stuff only related to me.
> 
> Additional to that when you cause some unrelated side effect in a driver we
> can much easier pinpoint the actual change later on when the patch is
> smaller.
> 
> > 
> > > This way I'm pretty sure Felix and I can give an rb on the amdgpu/amdkfd
> > > changes.
> > If you are worried to give r-b only for those then this can be done even
> > for larger patches. Just make your Reviewd-by more specific
> > R-b: name # For BLA BLA
> 
> Yeah, possible alternative but more work for me when I review it :)

I definitely do not want to add more work to reviewers and I completely
see how massive "flag days" like these are not popular but I really
didn't find a reasonable way around that would be both correct and
wouldn't add much more churn on the way. So if you really insist then I
would really appreciate a hint on the way to achive the same without any
above downsides.
-- 
Michal Hocko
SUSE Labs