Re: [RFC] Per file OOM badness

Michel Dänzer
2018-01-30T11:42:24Z

On 2018-01-30 12:36 PM, Nicolai HA?hnle wrote:
> On 30.01.2018 12:34, Michel DA?nzer wrote:
>> On 2018-01-30 12:28 PM, Christian KA?nig wrote:
>>> Am 30.01.2018 um 12:02 schrieb Michel DA?nzer:
>>>> On 2018-01-30 11:40 AM, Christian KA?nig wrote:
>>>>> Am 30.01.2018 um 10:43 schrieb Michel DA?nzer:
>>>>>> [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.
>
> Existing protocols pass DRM fds between processes though, don't they?
>
> Not child processes perhaps, but special-casing that seems like awful
> design.

Fair enough.

Can we disallow passing DRM file descriptors which have any buffers
allocated? :)

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