page allocator bug in 3.16?

[Thomas Hellstrom]

On 09/26/2014 02:28 PM, Rob Clark wrote:
> On Fri, Sep 26, 2014 at 6:45 AM, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>> On 09/26/2014 12:40 PM, Chuck Ebbert wrote:
>>> On Fri, 26 Sep 2014 09:15:57 +0200
>>> Thomas Hellstrom <thellstrom at vmware.com> wrote:
>>>
>>>> On 09/26/2014 01:52 AM, Peter Hurley wrote:
>>>>> On 09/25/2014 03:35 PM, Chuck Ebbert wrote:
>>>>>> There are six ttm patches queued for 3.16.4:
>>>>>>
>>>>>> drm-ttm-choose-a-pool-to-shrink-correctly-in-ttm_dma_pool_shrink_scan.patch
>>>>>> drm-ttm-fix-handling-of-ttm_pl_flag_topdown-v2.patch
>>>>>> drm-ttm-fix-possible-division-by-0-in-ttm_dma_pool_shrink_scan.patch
>>>>>> drm-ttm-fix-possible-stack-overflow-by-recursive-shrinker-calls.patch
>>>>>> drm-ttm-pass-gfp-flags-in-order-to-avoid-deadlock.patch
>>>>>> drm-ttm-use-mutex_trylock-to-avoid-deadlock-inside-shrinker-functions.patch
>>>>> Thanks for info, Chuck.
>>>>>
>>>>> Unfortunately, none of these fix TTM dma allocation doing CMA dma allocation,
>>>>> which is the root problem.
>>>>>
>>>>> Regards,
>>>>> Peter Hurley
>>>> The problem is not really in TTM but in CMA, There was a guy offering to
>>>> fix this in the CMA code but I guess he didn't probably because he
>>>> didn't receive any feedback.
>>>>
>>> Yeah, the "solution" to this problem seems to be "don't enable CMA on
>>> x86". Maybe it should even be disabled in the config system.
>> Or, as previously suggested, don't use CMA for order 0 (single page)
>> allocations....
> On devices that actually need CMA pools to arrange for memory to be in
> certain ranges, I think you probably do want to have order 0 pages
> come from the CMA pool.

But can the DMA subsystem or more specifically dma_alloc_coherent()
really guarantee such things? Isn't it better for such devices to use
CMA directly?

/Thomas


>
> Seems like disabling CMA on x86 (where it should be unneeded) is the
> better way, IMO
>
> BR,
> -R
>
>
>> /Thomas
>>
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