Free up completely empty Chunks, and return the memory to the OS

Detect any Chunk that's completely empty, deallocate it and return the
memory to the OS (as far as that's supported).

Change-Id: I6b6a77f2cdf478cbf16aad30a9cae37c98c6500e
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 22 insertions, 8 deletions

diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index 0a6dfb9170..ef36e62373 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -275,8 +275,9 @@ QString binary(quintptr) { return QString(); }
 #define SDUMP if (1) ; else qDebug
 #endif
 
-void Chunk::sweep()
+bool Chunk::sweep()
 {
+    bool hasUsedSlots = false;
     SDUMP() << "sweeping chunk" << this;
     HeapItem *o = realBase();
     bool lastSlotFree = false;
@@ -316,6 +317,7 @@ void Chunk::sweep()
             }
         }
         objectBitmap[i] = blackBitmap[i];
+        hasUsedSlots |= (blackBitmap[i] != 0);
         blackBitmap[i] = 0;
         extendsBitmap[i] = e;
         lastSlotFree = !((objectBitmap[i]|extendsBitmap[i]) >> (sizeof(quintptr)*8 - 1));
@@ -325,6 +327,7 @@ void Chunk::sweep()
         o += Chunk::Bits;
     }
     //    DEBUG << "swept chunk" << this << "freed" << slotsFreed << "slots.";
+    return hasUsedSlots;
 }
 
 void Chunk::freeAll()
@@ -579,12 +582,21 @@ void BlockAllocator::sweep()
 
 //    qDebug() << "BlockAlloc: sweep";
     usedSlotsAfterLastSweep = 0;
-    for (auto c : chunks) {
-        c->sweep();
-        c->sortIntoBins(freeBins, NumBins);
-//        qDebug() << "used slots in chunk" << c << ":" << c->nUsedSlots();
-        usedSlotsAfterLastSweep += c->nUsedSlots();
-    }
+
+    auto isFree = [this] (Chunk *c) {
+        bool isUsed = c->sweep();
+
+        if (isUsed) {
+            c->sortIntoBins(freeBins, NumBins);
+            usedSlotsAfterLastSweep += c->nUsedSlots();
+        } else {
+            chunkAllocator->free(c);
+        }
+        return !isUsed;
+    };
+
+    auto newEnd = std::remove_if(chunks.begin(), chunks.end(), isFree);
+    chunks.erase(newEnd, chunks.end());
 }
 
 void BlockAllocator::freeAll()
@@ -950,7 +962,8 @@ void MemoryManager::runGC()
 #ifndef QT_NO_DEBUG
         qDebug() << "    Triggered by alloc request of" << lastAllocRequestedSlots << "slots.";
 #endif
-        qDebug() << "Allocated" << totalMem << "bytes in" << blockAllocator.chunks.size() << "chunks";
+        size_t oldChunks = blockAllocator.chunks.size();
+        qDebug() << "Allocated" << totalMem << "bytes in" << oldChunks << "chunks";
         qDebug() << "Fragmented memory before GC" << (totalMem - usedBefore);
         dumpBins(&blockAllocator);
 
@@ -975,6 +988,7 @@ void MemoryManager::runGC()
         qDebug() << "Used memory before GC:" << usedBefore;
         qDebug() << "Used memory after GC:" << usedAfter;
         qDebug() << "Freed up bytes:" << (usedBefore - usedAfter);
+        qDebug() << "Freed up chunks:" << (oldChunks - blockAllocator.chunks.size());
         size_t lost = blockAllocator.allocatedMem() - memInBins - usedAfter;
         if (lost)
             qDebug() << "!!!!!!!!!!!!!!!!!!!!! LOST MEM:" << lost << "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!";