Failed to find memory space for buffer eviction
Christian König
ckoenig.leichtzumerken at gmail.com
Wed Jul 15 09:28:13 UTC 2020
Am 15.07.20 um 04:49 schrieb Felix Kuehling:
> Am 2020-07-14 um 4:28 a.m. schrieb Christian König:
>> Hi Felix,
>>
>> yes I already stumbled over this as well quite recently.
>>
>> See the following patch which I pushed to drm-misc-next just yesterday:
>>
>> commit e04be2310b5eac683ec03b096c0e22c4c2e23593
>> Author: Christian König <christian.koenig at amd.com>
>> Date: Mon Jul 6 17:32:55 2020 +0200
>>
>> drm/ttm: further cleanup ttm_mem_reg handling
>>
>> Stop touching the backend private pointer alltogether and
>> make sure we never put the same mem twice by.
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>> Reviewed-by: Madhav Chauhan <madhav.chauhan at amd.com>
>> Link: https://patchwork.freedesktop.org/patch/375613/
>>
>>
>> But this shouldn't have been problematic since we used a dummy value
>> for mem->mm_node in this case.
> Hmm, yeah, I was reading the code wrong. It's possible that I was really
> just out of GTT space. But see below.
It looks like it yes.
>> What could be problematic and result is an overrun is that TTM was
>> buggy and called put_node twice for the same memory.
>>
>> So I've seen that the code needs fixing as well, but I'm not 100% sure
>> how you ran into your problem.
> This is in the KFD eviction test, which deliberately overcommits VRAM in
> order to trigger lots of evictions. It will use some GTT space while BOs
> are evicted. But shouldn't it move them further out of GTT and into
> SYSTEM to free up GTT space?
Yes, exactly that should happen.
But for some reason it couldn't find a candidate to evict and the 14371
pages left are just a bit to small for the buffer.
Regards,
Christian.
> Your change "further cleanup ttm_mem_reg handling" removes a
> mem->mm_node = NULL in ttm_bo_handle_move_mem in exactly the case where
> a BO is moved from GTT to SYSTEM. I think that leads to a later put_node
> call not happening or amdgpu_gtt_mgr_del returning before incrementing
> mgr->available.
>
> I can try if cherry-picking your two fixes will help with the eviction test.
>
> Regards,
> Felix
>
>
>> Regards,
>> Christian.
>>
>> Am 14.07.20 um 02:44 schrieb Felix Kuehling:
>>> I'm running into this problem with the KFD EvictionTest. The log snippet
>>> below looks like it ran out of GTT space for the eviction of a 64MB
>>> buffer. But then it dumps the used and free space and shows plenty of
>>> free space.
>>>
>>> As I understand it, the per-page breakdown of used and free space shown
>>> by TTM is the GART space. So it's not very meaningful.
>>>
>>> What matters more is the GTT space managed by amdgpu_gtt_mgr.c. And
>>> that's where the problem is. It keeps track of available GTT space with
>>> an atomic counter in amdgpu_gtt_mgr.available. It gets decremented in
>>> amdgpu_gtt_mgr_new and incremented in amdgpu_gtt_mgr_del. The trouble
>>> is, that TTM doesn't call the latter for ttm_mem_regs that don't have an
>>> mm_node:
>>>
>>>> void ttm_bo_mem_put(struct ttm_buffer_object *bo, struct ttm_mem_reg
>>>> *mem)
>>>> {
>>>> struct ttm_mem_type_manager *man =
>>>> &bo->bdev->man[mem->mem_type];
>>>>
>>>> if (mem->mm_node)
>>>> (*man->func->put_node)(man, mem);
>>>> }
>>> GTT BOs that don't have GART space allocated, don't hate an mm_node. So
>>> the amdgpu_gtt_mgr.available counter doesn't get incremented when an
>>> unmapped GTT BO is freed, and eventually runs out of space.
>>>
>>> Now I know what the problem is, but I don't know how to fix it. Maybe a
>>> dummy-mm_node for unmapped GTT BOs, to trick TTM into calling our
>>> put_node callback? Or a change in TTM to call put_node unconditionally?
>>>
>>> Regards,
>>> Felix
>>>
>>>
>>> [ 360.082552] [TTM] Failed to find memory space for buffer
>>> 0x00000000264c823c eviction
>>> [ 360.090331] [TTM] No space for 00000000264c823c (16384 pages,
>>> 65536K, 64M)
>>> [ 360.090334] [TTM] placement[0]=0x00010002 (1)
>>> [ 360.090336] [TTM] has_type: 1
>>> [ 360.090337] [TTM] use_type: 1
>>> [ 360.090339] [TTM] flags: 0x0000000A
>>> [ 360.090341] [TTM] gpu_offset: 0xFF00000000
>>> [ 360.090342] [TTM] size: 1048576
>>> [ 360.090344] [TTM] available_caching: 0x00070000
>>> [ 360.090346] [TTM] default_caching: 0x00010000
>>> [ 360.090349] [TTM] 0x0000000000000400-0x0000000000000402: 2: used
>>> [ 360.090352] [TTM] 0x0000000000000402-0x0000000000000404: 2: used
>>> [ 360.090354] [TTM] 0x0000000000000404-0x0000000000000406: 2: used
>>> [ 360.090355] [TTM] 0x0000000000000406-0x0000000000000408: 2: used
>>> [ 360.090357] [TTM] 0x0000000000000408-0x000000000000040a: 2: used
>>> [ 360.090359] [TTM] 0x000000000000040a-0x000000000000040c: 2: used
>>> [ 360.090361] [TTM] 0x000000000000040c-0x000000000000040e: 2: used
>>> [ 360.090363] [TTM] 0x000000000000040e-0x0000000000000410: 2: used
>>> [ 360.090365] [TTM] 0x0000000000000410-0x0000000000000412: 2: used
>>> [ 360.090367] [TTM] 0x0000000000000412-0x0000000000000414: 2: used
>>> [ 360.090368] [TTM] 0x0000000000000414-0x0000000000000415: 1: used
>>> [ 360.090370] [TTM] 0x0000000000000415-0x0000000000000515: 256: used
>>> [ 360.090372] [TTM] 0x0000000000000515-0x0000000000000516: 1: used
>>> [ 360.090374] [TTM] 0x0000000000000516-0x0000000000000517: 1: used
>>> [ 360.090376] [TTM] 0x0000000000000517-0x0000000000000518: 1: used
>>> [ 360.090378] [TTM] 0x0000000000000518-0x0000000000000519: 1: used
>>> [ 360.090379] [TTM] 0x0000000000000519-0x000000000000051a: 1: used
>>> [ 360.090381] [TTM] 0x000000000000051a-0x000000000000051b: 1: used
>>> [ 360.090383] [TTM] 0x000000000000051b-0x000000000000051c: 1: used
>>> [ 360.090385] [TTM] 0x000000000000051c-0x000000000000051d: 1: used
>>> [ 360.090387] [TTM] 0x000000000000051d-0x000000000000051f: 2: used
>>> [ 360.090389] [TTM] 0x000000000000051f-0x0000000000000521: 2: used
>>> [ 360.090391] [TTM] 0x0000000000000521-0x0000000000000522: 1: used
>>> [ 360.090392] [TTM] 0x0000000000000522-0x0000000000000523: 1: used
>>> [ 360.090394] [TTM] 0x0000000000000523-0x0000000000000524: 1: used
>>> [ 360.090396] [TTM] 0x0000000000000524-0x0000000000000525: 1: used
>>> [ 360.090398] [TTM] 0x0000000000000525-0x0000000000000625: 256: used
>>> [ 360.090400] [TTM] 0x0000000000000625-0x0000000000000725: 256: used
>>> [ 360.090402] [TTM] 0x0000000000000725-0x0000000000000727: 2: used
>>> [ 360.090404] [TTM] 0x0000000000000727-0x00000000000007c0: 153: used
>>> [ 360.090406] [TTM] 0x00000000000007c0-0x0000000000000b8a: 970: used
>>> [ 360.090407] [TTM] 0x0000000000000b8a-0x0000000000000b8b: 1: used
>>> [ 360.090409] [TTM] 0x0000000000000b8b-0x0000000000000bcb: 64: used
>>> [ 360.090411] [TTM] 0x0000000000000bcb-0x0000000000000bcd: 2: used
>>> [ 360.090413] [TTM] 0x0000000000000bcd-0x0000000000040000: 259123:
>>> free
>>> [ 360.090415] [TTM] total: 261120, used 1997 free 259123
>>> [ 360.090417] [TTM] man size:1048576 pages, gtt available:14371 pages,
>>> usage:4039MB
>>>
>>>
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