linux-kernel - Re: [PATCH 2/2] drm: Revert syncobj timeline changes.

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Date:   Fri, 09 Nov 2018 14:26:58 -0800
From:   Eric Anholt <eric@...olt.net>
To:     zhoucm1 <zhoucm1@....com>, christian.koenig@....com,
        "dri-devel\@lists.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm: Revert syncobj timeline changes.

Eric Anholt <eric@...olt.net> writes:

> [ Unknown signature status ]
> zhoucm1 <zhoucm1@....com> writes:
>
>> On 2018年11月09日 00:52, Christian König wrote:
>>> Am 08.11.18 um 17:07 schrieb Koenig, Christian:
>>>> Am 08.11.18 um 17:04 schrieb Eric Anholt:
>>>>> Daniel suggested I submit this, since we're still seeing regressions
>>>>> from it.  This is a revert to before 48197bc564c7 ("drm: add syncobj
>>>>> timeline support v9") and its followon fixes.
>>>> This is a harmless false positive from lockdep, Chouming and I are
>>>> already working on a fix.
>>>
>>> On the other hand we had enough trouble with that patch, so if it 
>>> really bothers you feel free to add my Acked-by: Christian König 
>>> <christian.koenig@....com> and push it.
>> NAK, please no, I don't think this needed, the Warning totally isn't 
>> related to syncobj timeline, but fence-array implementation flaw, just 
>> exposed by syncobj.
>> In addition, Christian already has a fix for this Warning, I've tested. 
>> Please Christian send to public review.
>
> I backed out my revert of #2 (#1 still necessary) after adding the
> lockdep regression fix, and now my CTS run got oomkilled after just a
> few hours, with these notable lines in the unreclaimable slab info list:
>
> [ 6314.373099] drm_sched_fence        69095KB      69095KB
> [ 6314.373653] kmemleak_object       428249KB     428384KB
> [ 6314.373736] kmalloc-262144           256KB        256KB
> [ 6314.373743] kmalloc-131072           128KB        128KB
> [ 6314.373750] kmalloc-65536             64KB         64KB
> [ 6314.373756] kmalloc-32768           1472KB       1728KB
> [ 6314.373763] kmalloc-16384             64KB         64KB
> [ 6314.373770] kmalloc-8192             208KB        208KB
> [ 6314.373778] kmalloc-4096            2408KB       2408KB
> [ 6314.373784] kmalloc-2048             288KB        336KB
> [ 6314.373792] kmalloc-1024            1457KB       1512KB
> [ 6314.373800] kmalloc-512              854KB       1048KB
> [ 6314.373808] kmalloc-256              188KB        268KB
> [ 6314.373817] kmalloc-192            69141KB      69142KB
> [ 6314.373824] kmalloc-64             47703KB      47704KB
> [ 6314.373886] kmalloc-128            46396KB      46396KB
> [ 6314.373894] kmem_cache                31KB         35KB
>
> No results from kmemleak, though.

OK, it looks like the #2 revert probably isn't related to the OOM issue.
Running a single job on otherwise unused DRM, watching /proc/slabinfo
every second for drm_sched_fence, I get:

drm_sched_fence        0      0    192   21    1 : tunables   32   16    8 : slabdata      0      0      0 : globalstat       0      0     0    0    0    0    0    0    0 : cpustat      0      0      0      0
drm_sched_fence       16     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
drm_sched_fence       13     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
drm_sched_fence        6     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
drm_sched_fence        4     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
drm_sched_fence        2     21    192   21    1 : tunables   32   16    8 : slabdata      1      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0
drm_sched_fence        0     21    192   21    1 : tunables   32   16    8 : slabdata      0      1      0 : globalstat      16     16     1    0    0    0    0    0    0 : cpustat      5      1      6      0

So we generate a ton of fences, and I guess free them slowly because of
RCU?  And presumably kmemleak was sucking up lots of memory because of
how many of these objects were laying around.

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