base: Avoid purging more discardable memory than necessary.

base/memory/discardable_memory_provider_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/memory/discardable_memory_provider.h"
 
 #include "base/bind.h"
 #include "base/memory/discardable_memory.h"
 #include "base/run_loop.h"
 #include "base/synchronization/waitable_event.h"
@@ skipping 214 matching lines @@
 
   SetBytesToReclaimUnderModeratePressure(1024);
   SetDiscardableMemoryLimit(2048);
 
   EXPECT_NE(DISCARDABLE_MEMORY_FAILED, discardable(2)->Lock());
   EXPECT_NE(DISCARDABLE_MEMORY_SUCCESS, discardable(1)->Lock());
   // 0 should still be locked.
   EXPECT_NE(static_cast<void*>(NULL), Memory(discardable(0)));
 }
 
+// Verify that no more memory than necessary was discarded after changing
+// memory limit.
+TEST_P(DiscardableMemoryProviderPermutationTest, LRUDiscardedAmount) {
+  SetBytesToReclaimUnderModeratePressure(2048);
+  SetDiscardableMemoryLimit(4096);
+
+  CreateAndUseDiscardableMemory();
+
+  SetDiscardableMemoryLimit(2048);
+
+  EXPECT_EQ(DISCARDABLE_MEMORY_SUCCESS, discardable(2)->Lock());
+  EXPECT_EQ(DISCARDABLE_MEMORY_PURGED, discardable(1)->Lock());
+  // 0 should still be locked.
+  EXPECT_NE(static_cast<void*>(NULL), Memory(discardable(0)));
+}
+
 TEST_P(DiscardableMemoryProviderPermutationTest,
        CriticalPressureFreesAllUnlocked) {
   CreateAndUseDiscardableMemory();
 
   MemoryPressureListener::NotifyMemoryPressure(
       MemoryPressureListener::MEMORY_PRESSURE_CRITICAL);
   RunLoop().RunUntilIdle();
 
   for (int i = 0; i < 3; ++i) {
     if (i == 0)
@@ skipping 93 matching lines @@
       Bind(&ThreadedDiscardableMemoryProviderTest::UseMemoryHelper,
            Unretained(this)));
   memory_usage_thread_.message_loop()->PostTask(
       FROM_HERE,
       Bind(&ThreadedDiscardableMemoryProviderTest::SignalHelper,
            Unretained(this)));
   thread_sync_.Wait();
 }
 
 }  // namespace base