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Stop running shrinking gcs & simplify GC logic.

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Shrinking GCs dump the JITted code, which leads to redundant recompilations, lowers performance, and makes profiling JS more difficult.
They may still happen if the runtime is at risk of OOM.
This commit is contained in:
Lancelot de Ferrière
2024-11-23 18:36:23 +01:00
committed by wraitii
parent d262eb8757
commit af32d386b9
8 changed files with 96 additions and 122 deletions
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source/scriptinterface/ScriptContext.cpp
+65 -91
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@@ -80,12 +80,12 @@ void GCSliceCallbackHook(JSContext* UNUSED(cx), JS::GCProgress progress, const J
#endif
}
std::shared_ptr<ScriptContext> ScriptContext::CreateContext(int contextSize, int heapGrowthBytesGCTrigger)
std::shared_ptr<ScriptContext> ScriptContext::CreateContext(int contextSize, uint32_t heapGrowthBytesGCTrigger)
{
return std::make_shared<ScriptContext>(contextSize, heapGrowthBytesGCTrigger);
}
ScriptContext::ScriptContext(int contextSize, int heapGrowthBytesGCTrigger):
ScriptContext::ScriptContext(int contextSize, uint32_t heapGrowthBytesGCTrigger):
m_JobQueue{std::make_unique<Script::JobQueue>()},
m_ContextSize{contextSize},
m_HeapGrowthBytesGCTrigger{heapGrowthBytesGCTrigger}
@@ -112,6 +112,14 @@ ScriptContext::ScriptContext(int contextSize, int heapGrowthBytesGCTrigger):
JS_SetGCParameter(m_cx, JSGC_INCREMENTAL_GC_ENABLED, true);
JS_SetGCParameter(m_cx, JSGC_PER_ZONE_GC_ENABLED, false);
// Attempt to turn off Spidermonkey-led GCs.
JS_SetGCParameter(m_cx, JSGC_HEAP_GROWTH_FACTOR, contextSize);
JS_SetGCParameter(m_cx, JSGC_LOW_FREQUENCY_HEAP_GROWTH, 300);
JS_SetGCParameter(m_cx, JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH, 500);
JS_SetGCParameter(m_cx, JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH, 300);
JS_SetGCParameter(m_cx, JSGC_SLICE_TIME_BUDGET_MS, 10);
JS_SetOffthreadIonCompilationEnabled(m_cx, true);
// For GC debugging:
@@ -166,105 +174,71 @@ void ScriptContext::UnRegisterRealm(JS::Realm* realm)
}
#define GC_DEBUG_PRINT 0
void ScriptContext::MaybeIncrementalGC(double delay)
void ScriptContext::MaybeIncrementalGC()
{
PROFILE2("MaybeIncrementalGC");
if (JS::IsIncrementalGCEnabled(m_cx))
if (!JS::IsIncrementalGCEnabled(m_cx))
return;
// The idea is to get the heap size after a completed GC and trigger the next GC
// when the heap size has reached m_LastGCBytes + X.
// Spidermonkey allocates memory arenas of 4KB for JS heap data.
// At the end of a GC, any such arena that became empty is freed.
// On shrinking GCs, spidermonkey further defragments the arenas, which effectively frees more memory but costs time.
// In practice, shrinking GCs also dump JITted code and the defragmentation is not worth it for 0 A.D.
// The regular GCs also free quite a bit of memory anyways, and non-full arenas get used for new objects.
const uint32_t gcBytes = JS_GetGCParameter(m_cx, JSGC_BYTES);
#if GC_DEBUG_PRINT
printf("gcBytes: %i KB, last of %i KB\n", gcBytes / 1024, m_LastGCBytes / 1024);
#endif
// The memory freeing happens mostly in the background, so we can't rely on the value on the last incremental slice.
// To fix that, just remember a 'minimum' value.
if (m_LastGCBytes > gcBytes || m_LastGCBytes == 0)
{
// The idea is to get the heap size after a completed GC and trigger the next GC when the heap size has
// reached m_LastGCBytes + X.
// In practice it doesn't quite work like that. When the incremental marking is completed, the sweeping kicks in.
// The sweeping actually frees memory and it does this in a background thread (if JS_USE_HELPER_THREADS is set).
// While the sweeping is happening we already run scripts again and produce new garbage.
const js::SliceBudget GCSliceTimeBudget = js::SliceBudget(js::TimeBudget(30)); // Milliseconds an incremental slice is allowed to run
// Have a minimum time in seconds to wait between GC slices and before starting a new GC to distribute the GC
// load and to hopefully make it unnoticeable for the player. This value should be high enough to distribute
// the load well enough and low enough to make sure we don't run out of memory before we can start with the
// sweeping.
if (timer_Time() - m_LastGCCheck < delay)
return;
m_LastGCCheck = timer_Time();
int gcBytes = JS_GetGCParameter(m_cx, JSGC_BYTES);
#if GC_DEBUG_PRINT
std::cout << "gcBytes: " << gcBytes / 1024 << " KB" << std::endl;
printf("Setting m_LastGCBytes: %d KB \n", gcBytes / 1024);
#endif
m_LastGCBytes = gcBytes;
}
// Run an additional incremental GC slice if the currently running incremental GC isn't over yet
// ... or
// start a new incremental GC if the JS heap size has grown enough for a GC to make sense
if (JS::IsIncrementalGCInProgress(m_cx) || (gcBytes - m_LastGCBytes > m_HeapGrowthBytesGCTrigger))
{
#if GC_DEBUG_PRINT
if (JS::IsIncrementalGCInProgress(m_cx))
printf("An incremental GC cycle is in progress. \n");
else
printf("GC needed because JSGC_BYTES - m_LastGCBytes > m_HeapGrowthBytesGCTrigger \n"
" JSGC_BYTES: %d KB \n m_LastGCBytes: %d KB \n m_HeapGrowthBytesGCTrigger: %d KB \n",
gcBytes / 1024,
m_LastGCBytes / 1024,
m_HeapGrowthBytesGCTrigger / 1024);
#endif
if (m_LastGCBytes > gcBytes || m_LastGCBytes == 0)
{
#if GC_DEBUG_PRINT
printf("Setting m_LastGCBytes: %d KB \n", gcBytes / 1024);
#endif
m_LastGCBytes = gcBytes;
}
// Run an additional incremental GC slice if the currently running incremental GC isn't over yet
// ... or
// start a new incremental GC if the JS heap size has grown enough for a GC to make sense
if (JS::IsIncrementalGCInProgress(m_cx) || (gcBytes - m_LastGCBytes > m_HeapGrowthBytesGCTrigger))
{
#if GC_DEBUG_PRINT
if (JS::IsIncrementalGCInProgress(m_cx))
printf("An incremental GC cycle is in progress. \n");
else
printf("GC needed because JSGC_BYTES - m_LastGCBytes > m_HeapGrowthBytesGCTrigger \n"
" JSGC_BYTES: %d KB \n m_LastGCBytes: %d KB \n m_HeapGrowthBytesGCTrigger: %d KB \n",
gcBytes / 1024,
m_LastGCBytes / 1024,
m_HeapGrowthBytesGCTrigger / 1024);
if (!JS::IsIncrementalGCInProgress(m_cx))
printf("Starting incremental GC \n");
else
printf("Running incremental GC slice \n");
#endif
// A hack to make sure we never exceed the context size because we can't collect the memory
// fast enough.
if (gcBytes > m_ContextSize / 2)
{
if (JS::IsIncrementalGCInProgress(m_cx))
{
#if GC_DEBUG_PRINT
printf("Finishing incremental GC because gcBytes > m_ContextSize / 2. \n");
#endif
PrepareZonesForIncrementalGC();
JS::FinishIncrementalGC(m_cx, JS::GCReason::API);
}
else
{
if (gcBytes > m_ContextSize * 0.75)
{
ShrinkingGC();
#if GC_DEBUG_PRINT
printf("Running shrinking GC because gcBytes > m_ContextSize * 0.75. \n");
#endif
}
else
{
#if GC_DEBUG_PRINT
printf("Running full GC because gcBytes > m_ContextSize / 2. \n");
#endif
JS_GC(m_cx);
}
}
}
else
{
#if GC_DEBUG_PRINT
if (!JS::IsIncrementalGCInProgress(m_cx))
printf("Starting incremental GC \n");
else
printf("Running incremental GC slice \n");
#endif
PrepareZonesForIncrementalGC();
if (!JS::IsIncrementalGCInProgress(m_cx))
JS::StartIncrementalGC(m_cx, JS::GCOptions::Normal, JS::GCReason::API, GCSliceTimeBudget);
else
JS::IncrementalGCSlice(m_cx, JS::GCReason::API, GCSliceTimeBudget);
}
m_LastGCBytes = gcBytes;
}
// There is a tradeoff between this time and the number of frames we must run GCs on, but overall we should prioritize smooth framerates.
const js::SliceBudget GCSliceTimeBudget = js::SliceBudget(js::TimeBudget(6)); // Milliseconds an incremental slice is allowed to run. SM respects this fairly well.
PrepareZonesForIncrementalGC();
if (!JS::IsIncrementalGCInProgress(m_cx))
JS::StartIncrementalGC(m_cx, JS::GCOptions::Normal, JS::GCReason::API, GCSliceTimeBudget);
else
JS::IncrementalGCSlice(m_cx, JS::GCReason::API, GCSliceTimeBudget);
// Reset this here so that the minimum gets cleared.
m_LastGCBytes = gcBytes;
}
}