Spilling from device
By default, Dask-CUDA enables spilling from GPU to host memory when a GPU reaches a memory utilization of 80%.
This can be changed to suit the needs of a workload, or disabled altogether, by explicitly setting
This parameter accepts an integer or string memory size, or a float representing a percentage of the GPU’s total memory:
from dask_cuda import LocalCUDACluster cluster = LocalCUDACluster(device_memory_limit=50000) # spilling after 50000 bytes cluster = LocalCUDACluster(device_memory_limit="5GB") # spilling after 5 GB cluster = LocalCUDACluster(device_memory_limit=0.3) # spilling after 30% memory utilization
Memory spilling can be disabled by setting
device_memory_limit to 0:
cluster = LocalCUDACluster(device_memory_limit=0) # spilling disabled
The same applies for
dask cuda worker, and spilling can be controlled by setting
$ dask scheduler distributed.scheduler - INFO - Scheduler at: tcp://127.0.0.1:8786 $ dask cuda worker --device-memory-limit 50000 $ dask cuda worker --device-memory-limit 5GB $ dask cuda worker --device-memory-limit 0.3 $ dask cuda worker --device-memory-limit 0
The regular spilling in Dask and Dask-CUDA has some significate issues. Instead of tracking individual objects, it tracks task outputs. This means that a task returning a collection of CUDA objects will either spill all of the CUDA objects or none of them. Other issues includes object duplication, wrong spilling order, and non-tracking of sharing device buffers (see: https://github.com/dask/distributed/issues/4568#issuecomment-805049321).
In order to address all of these issues, Dask-CUDA introduces JIT-Unspilling, which can improve performance and memory usage significantly. For workloads that require significant spilling (such as large joins on infrastructure with less available memory than data) we have often seen greater than 50% improvement (i.e., something taking 300 seconds might take only 110 seconds). For workloads that do not, we would not expect to see much difference.
In order to enable JIT-Unspilling use the
>>> import dask​ >>> from distributed import Client​ >>> from dask_cuda import LocalCUDACluster​ >>> cluster = LocalCUDACluster(n_workers=10, device_memory_limit="1GB", jit_unspill=True)​ >>> client = Client(cluster)​ >>> with dask.config.set(jit_unspill=True):​ ... cluster = LocalCUDACluster(n_workers=10, device_memory_limit="1GB")​ ... client = Client(cluster)
Or set the worker argument
$ dask scheduler distributed.scheduler - INFO - Scheduler at: tcp://127.0.0.1:8786 $ dask cuda worker --enable-jit-unspill​
Or environment variable
$ dask scheduler distributed.scheduler - INFO - Scheduler at: tcp://127.0.0.1:8786 $ DASK_JIT_UNSPILL=True dask cuda worker​
JIT-Unspill wraps CUDA objects, such as
cudf.Dataframe, in a
Objects proxied by an instance of
ProxyObject will be JIT-deserialized when
accessed. The instance behaves as the proxied object and can be accessed/used
just like the proxied object.
ProxyObject has some limitations and doesn’t mimic the proxied object perfectly.
Most noticeable, type checking using
instance() works as expected but direct
type checking doesn’t:
>>> import numpy as np >>> from dask_cuda.proxy_object import asproxy >>> x = np.arange(3) >>> isinstance(asproxy(x), type(x)) True >>> type(asproxy(x)) is type(x) False
Thus, if encountering problems remember that it is always possible to use
to access the proxied object directly, or set
to enable compatibility mode, which automatically calls
unproxy() on all function inputs.