Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC] Per file OOM badness
To:     christian.koenig@amd.com, Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <guro@fb.com>
Cc:     linux-mm@kvack.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org
References: <20180118170006.GG6584@dhcp22.suse.cz>
 <20180123152659.GA21817@castle.DHCP.thefacebook.com>
 <20180123153631.GR1526@dhcp22.suse.cz>
 <ccac4870-ced3-f169-17df-2ab5da468bf0@daenzer.net>
 <20180124092847.GI1526@dhcp22.suse.cz>
 <583f328e-ff46-c6a4-8548-064259995766@daenzer.net>
 <20180124110141.GA28465@dhcp22.suse.cz>
 <36b49523-792d-45f9-8617-32b6d9d77418@daenzer.net>
 <20180124115059.GC28465@dhcp22.suse.cz>
 <381a868c-78fd-d0d1-029e-a2cf4ab06d37@gmail.com>
 <20180130093145.GE25930@phenom.ffwll.local>
 <3db43c1a-59b8-af86-2b87-c783c629f512@daenzer.net>
 <3026d8c5-9313-cb8b-91ef-09c02baf27db@amd.com>
 <445628d3-677c-a9f8-171f-7d74a603c61d@daenzer.net>
 <dce6d244-36c7-7452-97f5-7437bd78cfcc@gmail.com>
From:   =?UTF-8?Q?Michel_D=c3=a4nzer?= <michel@daenzer.net>
Message-ID: <e511ba10-7032-36cc-f22c-2f6bb05f9f6e@daenzer.net>
Date:   Tue, 30 Jan 2018 12:34:18 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <dce6d244-36c7-7452-97f5-7437bd78cfcc@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-CA
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018-01-30 12:28 PM, Christian König wrote:
> Am 30.01.2018 um 12:02 schrieb Michel Dänzer:
>> On 2018-01-30 11:40 AM, Christian König wrote:
>>> Am 30.01.2018 um 10:43 schrieb Michel Dänzer:
>>>> [SNIP]
>>>>> Would it be ok to hang onto potentially arbitrary mmget references
>>>>> essentially forever? If that's ok I think we can do your process based
>>>>> account (minus a few minor inaccuracies for shared stuff perhaps,
>>>>> but no
>>>>> one cares about that).
>>>> Honestly, I think you and Christian are overthinking this. Let's try
>>>> charging the memory to every process which shares a buffer, and go from
>>>> there.
>>> My problem is that this needs to be bullet prove.
>>>
>>> For example imagine an application which allocates a lot of BOs, then
>>> calls fork() and let the parent process die. The file descriptor lives
>>> on in the child process, but the memory is not accounted against the
>>> child.
>> What exactly are you referring to by "the file descriptor" here?
> 
> The file descriptor used to identify the connection to the driver. In
> other words our drm_file structure in the kernel.
> 
>> What happens to BO handles in general in this case? If both parent and
>> child process keep the same handle for the same BO, one of them
>> destroying the handle will result in the other one not being able to use
>> it anymore either, won't it?
> Correct.
> 
> That usage is actually not useful at all, but we already had
> applications which did exactly that by accident.
> 
> Not to mention that somebody could do it on purpose.

Can we just prevent child processes from using their parent's DRM file
descriptors altogether? Allowing it seems like a bad idea all around.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer