Increase max TLH for non-batch clear platforms

For non-batch TLH clear platform (currently only those based on X h/w) the maximum size is increased to 1MB (from 128K default set by OMR). This allows better scaling on high allocating/high CPU count configurations. Batch clearing platforms stays at 128K max, since clearing too much in a batch may flush useful data from CPU data caches. Signed-off-by: Aleksandar Micic <[email protected]>
eclipse-openj9 · Jul 30, 2024 · 4c2f109 · 4c2f109
1 parent d776a4a
commit 4c2f109
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Showing 4 changed files with 24 additions and 1 deletion.
diff --git a/runtime/gc_base/GCExtensions.cpp b/runtime/gc_base/GCExtensions.cpp
@@ -103,6 +103,10 @@ MM_GCExtensions::initialize(MM_EnvironmentBase *env)
 	getJavaVM()->jniArrayCacheMaxSize = J9_GC_JNI_ARRAY_CACHE_SIZE;
 #endif /* J9VM_GC_JNI_ARRAY_CACHE */
 
+	/* We increase default max TLH size from OMR default value to allow non-batch clear TLH platforms to benefit from it.
+	 * Platforms that use batch clearing (see batchClearTLH)  will override later this with a smaller value */
+	tlhMaximumSize = J9_MAXIMUM_TLH_SIZE;
+
 #if defined(J9VM_GC_THREAD_LOCAL_HEAP)
 	getJavaVM()->gcInfo.tlhThreshold = J9_GC_TLH_THRESHOLD;
 	getJavaVM()->gcInfo.tlhSize = J9_GC_TLH_SIZE;

diff --git a/runtime/gc_base/GCExtensions.hpp b/runtime/gc_base/GCExtensions.hpp
@@ -81,6 +81,12 @@ class MM_IdleGCManager;
 #define MINIMUM_SURVIVOR_MINIMUM_FREESIZE 	512
 #define MINIMUM_SURVIVOR_THRESHOLD 			512
 
+
+#define J9_MAXIMUM_TLH_SIZE (1024 * 1024)
+#if defined(J9VM_GC_BATCH_CLEAR_TLH)
+#define J9_MAXIMUM_TLH_SIZE_BATCH_CLEAR (128 * 1024)
+#endif /* defined(J9VM_GC_BATCH_CLEAR_TLH) */
+
 /**
  * @todo Provide class documentation
  * @ingroup GC_Base
@@ -193,6 +199,8 @@ class MM_GCExtensions : public MM_GCExtensionsBase {
 
 	UserSpecifiedParameters userSpecifiedParameters; /**< A collection of user-speicifed parameters */
 
+	bool tlhMaximumSizeSpecified; /**< true, if tlhMaximumSize specified by a command line option */
+
 	bool dynamicHeapAdjustmentForRestore; /**< If set to true, the default heuristic-calculated softmx is prioritized over the user-specified values. */
 	/**
 	 * Values for com.ibm.oti.vm.VM.J9_JIT_STRING_DEDUP_POLICY
@@ -417,6 +425,7 @@ class MM_GCExtensions : public MM_GCExtensionsBase {
 		, objectListFragmentCount(0)
 		, numaCommonThreadClassNamePatterns(NULL)
 		, userSpecifiedParameters()
+		, tlhMaximumSizeSpecified(false)
 		, dynamicHeapAdjustmentForRestore(false)
 		, stringDedupPolicy(J9_JIT_STRING_DEDUP_POLICY_UNDEFINED)
 		, _asyncCallbackKey(-1)

diff --git a/runtime/gc_modron_startup/mmhelpers.cpp b/runtime/gc_modron_startup/mmhelpers.cpp
@@ -63,7 +63,16 @@ extern void initializeVerboseFunctionTableWithDummies(J9MemoryManagerVerboseInte
 void
 allocateZeroedTLHPages(J9JavaVM *javaVM, UDATA flag)
 {
-	MM_GCExtensions::getExtensions(javaVM)->batchClearTLH = (flag != 0) ? 1 : 0;
+	MM_GCExtensions *ext = MM_GCExtensions::getExtensions(javaVM);
+
+	ext->batchClearTLH = (flag != 0) ? 1 : 0;
+
+	/* For batch clearing limit maximum size (since clearing too much may flush useful data from CPU data caches).
+	 * Apply the limit only if user did not specify another value.
+	 */
+	if (ext->batchClearTLH && !ext->tlhMaximumSizeSpecified) {
+		ext->tlhMaximumSize = OMR_MIN(J9_MAXIMUM_TLH_SIZE_BATCH_CLEAR, ext->tlhMaximumSize);
+	}
 }
 
 /**

diff --git a/runtime/gc_modron_startup/mmparseXgc.cpp b/runtime/gc_modron_startup/mmparseXgc.cpp
@@ -73,6 +73,7 @@ j9gc_initialize_parse_gc_colon(J9JavaVM *javaVM, char **scan_start)
 		if(!scan_udata_helper(javaVM, scan_start, &extensions->tlhMaximumSize, "tlhMaximumSize=")) {
 			goto _error;
 		}
+		extensions->tlhMaximumSizeSpecified = true;
 		goto _exit;
 	}
 	if(try_scan(scan_start, "tlhIncrementSize=")) {