Does gather() clear memory

I am running in to memory limits on my GPUs. I know I can reset(gpuDevice) to clear all memory on the device, however, I would like to move arrays one at a time from GPU memory to memory and then clear the orginal GPU version. Does gather() also clear the GPU memory after copying/moving to memory?

If not, what would be the best way to achieve this?

Answer 1

[Joss Knight]

gather creates a copy of the array in main memory. Clearing a gpuArray variable will release its memory. So if you replace a gpuArray variable x with gather(x) then that will clear the gpuArray and release the memory. In other words

x = gather(x);

releases memory, but

y = gather(x);

does not, because x is still a gpuArray.

Hope that helps.

Note that MATLAB pools GPU memory, so memory available to MATLAB may continue to appear used in the Task Manager. You can get rid of this behaviour by setting the gpuDevice CachePolicy property to "minimum".

[James]

Thanks! Just what I was looking for

[James]

@Joss Knight Couple of follow ups as I still have a memory leak somewhere.

1. Does clear also release GPU arrays?
2. How about something like `tmp = rand(1000, 1, "gpuArray") <= 0.01`? Is the GPU array released automatically?

[Joss Knight]

Yes, clear will release GPU memory used by the cleared variable.

tmp = rand(1000, 1, "gpuArray") <= 0.01 creates a temporary 1000-by-1 array of double on the GPU, which will be cleared at the end of the operation, but tmp will now contain a 1000-by-1 array of logical on the GPU. Also, this comparison will be performed lazily so the temporary variable will not be released unless you display tmp or do something else to cause GPU synchronization.

[James]

Perfect, thank you!

Answer 2

[Matt J]

It seems to for me:

>> A=gpuArray.rand(300,300,300);

>> gpuDevice().AvailableMemory

ans =

3.1956e+09

>> A=gather(A);

>> gpuDevice().AvailableMemory

ans =

3.4116e+09

[James]

Great, thanks, I have the same