Re: [PATCH 1/8] mm: cma: introduce cma_release_nowait()

[Mike Kravetz]

On 3/29/21 12:46 AM, Michal Hocko wrote:
> On Fri 26-03-21 14:32:01, Mike Kravetz wrote:
> [...]
>> - Just change the mutex to an irq safe spinlock.
> 
> Yes please.
> 
>>   AFAICT, the potential
>>   downsides could be:
>>   - Interrupts disabled during long bitmap scans
> 
> How large those bitmaps are in practice?
> 
>>   - Wasted cpu cycles (spinning) if there is much contention on lock
>>   Both of these would be more of an issue on small/embedded systems. I
>>   took a quick look at the callers of cma_alloc/cma_release and nothing
>>   stood out that could lead to high degrees of contention.  However, I
>>   could have missed something.
> 
> If this is really a practical concern then we can try a more complex
> solution based on some data.
> 

Ok, I will send v2 with this approach.  Adding Barry and Will on Cc: as
they were involved in adding more cma use cases for dma on arm.

-- 
Mike Kravetz