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

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On 2018年11月12日 18:16, Christian König wrote:
Am 09.11.18 um 23:26 schrieb Eric Anholt:
Eric Anholt <eric@xxxxxxxxxx> writes:

[ Unknown signature status ]
zhoucm1 <zhoucm1@xxxxxxx> 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@xxxxxxx> 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.
Before you judge if it is memleak, to be honest, you can scan it first.
 
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.

That is certainly possible. Another possibility is that we don't drop the reference in dma-fence-array early enough.

E.g. the dma-fence-array will keep the reference to its fences until it is destroyed, which is a bit late when you chain multiple dma-fence-array objects together.
Good point, but need to confirm.


David can you take a look at this and propose a fix? That would probably be good to have fixed in dma-fence-array separately to the timeline work.
Yeah,  I would find a free time for it.

Thanks,
David Zhou

Thanks,
Christian.


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