Bug 1093307 - Part 2: Make OOM flushing paths more straightforward; r=jonco

--HG--
extra : rebase_source : 4634215f64ea96c2057f4ff609119b2a6cad008f

js/src/gc/GCRuntime.h

@@ -498,7 +498,7 @@ class GCRuntime
      * Must be called either during the GC or with the GC lock taken.
      */
     Chunk *expireEmptyChunkPool(bool shrinkBuffers, const AutoLockGC &lock);
-    void freeEmptyChunks(JSRuntime *rt);
+    void freeEmptyChunks(JSRuntime *rt, const AutoLockGC &lock);
     void freeChunkList(Chunk *chunkListHead);
     void prepareToFreeChunk(ChunkInfo &info);
     void releaseChunk(Chunk *chunk);
@@ -543,6 +543,7 @@ class GCRuntime
     bool sweepPhase(SliceBudget &sliceBudget);
     void endSweepPhase(bool lastGC);
     void sweepZones(FreeOp *fop, bool lastGC);
+    void decommitAllWithoutUnlocking(const AutoLockGC &lock);
     void decommitArenasFromAvailableList(Chunk **availableListHeadp);
     void decommitArenas();
     void expireChunksAndArenas(bool shouldShrink, const AutoLockGC &lock);

js/src/jsgc.cpp

@@ -744,15 +744,22 @@ GCRuntime::expireEmptyChunkPool(bool shrinkBuffers, const AutoLockGC &lock)
     return freeList;
 }
 
-void
-GCRuntime::freeEmptyChunks(JSRuntime *rt)
+static void
+FreeChunkPool(JSRuntime *rt, ChunkPool &pool)
 {
-    for (ChunkPool::Enum e(emptyChunks_); !e.empty();) {
+    for (ChunkPool::Enum e(pool); !e.empty();) {
         Chunk *chunk = e.front();
         e.removeAndPopFront();
         MOZ_ASSERT(!chunk->info.numArenasFreeCommitted);
         FreeChunk(rt, chunk);
     }
+    MOZ_ASSERT(pool.count() == 0);
+}
+
+void
+GCRuntime::freeEmptyChunks(JSRuntime *rt, const AutoLockGC &lock)
+{
+    FreeChunkPool(rt, emptyChunks(lock));
 }
 
 void
@@ -1422,7 +1429,7 @@ GCRuntime::finish()
         chunkSet.clear();
     }
 
-    freeEmptyChunks(rt);
+    FreeChunkPool(rt, emptyChunks_);
 
     if (rootsHash.initialized())
         rootsHash.clear();
@@ -3122,6 +3129,25 @@ GCRuntime::maybePeriodicFullGC()
 #endif
 }
 
+// Do all possible decommit immediately from the current thread without
+// releasing the GC lock or allocating any memory.
+void
+GCRuntime::decommitAllWithoutUnlocking(const AutoLockGC &lock)
+{
+    MOZ_ASSERT(emptyChunks(lock).count() == 0);
+    for (Chunk *chunk = *getAvailableChunkList(); chunk; chunk = chunk->info.next) {
+        for (size_t i = 0; i < ArenasPerChunk; ++i) {
+            if (chunk->decommittedArenas.get(i) || chunk->arenas[i].aheader.allocated())
+                continue;
+
+            if (MarkPagesUnused(&chunk->arenas[i], ArenaSize)) {
+                chunk->info.numArenasFreeCommitted--;
+                chunk->decommittedArenas.set(i);
+            }
+        }
+    }
+}
+
 void
 GCRuntime::decommitArenasFromAvailableList(Chunk **availableListHeadp)
 {
@@ -6216,7 +6242,12 @@ GCRuntime::onOutOfMallocMemory()
 
     // Throw away any excess chunks we have lying around.
     AutoLockGC lock(rt);
-    expireChunksAndArenas(true, lock);
+    freeEmptyChunks(rt, lock);
+
+    // Immediately decommit as many arenas as possible in the hopes that this
+    // might let the OS scrape together enough pages to satisfy the failing
+    // malloc request.
+    decommitAllWithoutUnlocking(lock);
 }
 
 void