add note for windowing distribution

dmlc · May 9, 2019 · 0b8bff5 · 0b8bff5
1 parent 90009b8
commit 0b8bff5
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/src/common/host_device_vector.h b/src/common/host_device_vector.h
@@ -110,6 +110,9 @@ class GPUDistribution {
     return GPUDistribution(devices, granularity, 0, std::vector<size_t>());
   }
 
+  // NOTE(rongou): Explicit offsets don't necessarily cover the whole vector. Sections before the
+  // first shard or after the last shard may be on host only. This windowing is done in the GPU
+  // predictor for external memory support.
   static GPUDistribution Explicit(GPUSet devices, std::vector<size_t> offsets) {
     return GPUDistribution(devices, 1, 0, std::move(offsets));
   }