[llvm] [AMDGPU][Offload] Enable memory manager use for up to ~3GB allocation size in omp_target_alloc (PR #151882)

[Joseph Huber via llvm-commits]

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@@ -2944,6 +2944,41 @@ struct AMDGPUDeviceTy : public GenericDeviceTy, AMDGenericDeviceTy {
     return Plugin::success();
   }
 
+  bool checkIfCoarseGrainMemoryNearOrAbove64GB() {
+    for (AMDGPUMemoryPoolTy *Pool : AllMemoryPools) {
+      if (Pool->isGlobal() && Pool->isCoarseGrained()) {
+        uint64_t Value;
+        hsa_status_t Status =
+            Pool->getAttrRaw(HSA_AMD_MEMORY_POOL_INFO_SIZE, Value);
+        if (Status != HSA_STATUS_SUCCESS)
+          continue;
+        constexpr uint64_t Almost64Gig = 0xFF0000000;
+        if (Value >= Almost64Gig)
+          return true;
+      }
+    }
+    return false; // CoarseGrain pool w/ 64GB or more capacity not found
+  }
+
+  size_t getMemoryManagerSizeThreshold() override {
+    // Targeting high memory capacity GPUs such as
+    // MI210 or later data center GPUs.
+    if (checkIfCoarseGrainMemoryNearOrAbove64GB()) {
+      // Set GenericDeviceTy::MemoryManager's Threshold to ~3GB,
+      // if threshold is not already set by ENV var
+      // LIBOMPTARGET_MEMORY_MANAGER_THRESHOLD.
+      // This MemoryManager is used for omp_target_alloc(), OpenMP
+      // (non-usm) map clause, etc.
+      //
+      // Ideally, this kind of pooling is best performed at
+      // a common level (e.g, user side of HSA) between OpenMP and HIP
+      // but that feature does not exist (yet).
+      constexpr size_t Almost3Gig = 3000000000u;
+      return Almost3Gig;
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jhuber6 wrote:

I think just returning `3ul * 1024 * 1024 * 1024 /* 3 GiB */;` would be clearer.

https://github.com/llvm/llvm-project/pull/151882