Relax asserts in arena_test

Summary:
Commit c67d2068 did not fix all test conditions
which use Arena::MemoryAllocatedBytes() (see Travis failure
https://travis-ci.org/facebook/rocksdb/jobs/79957700). The assumption of that
commit was that aligned allocations do not call Arena::AllocateNewBlock(), so
malloc_usable_block_size() would not be used for Arena::MemoryAllocatedBytes().
However, there is a code path where Arena::AllocateAligned() calls
AllocateFallback() which in turn calls Arena::AllocateNewBlock(), so
Arena::MemoryAllocatedBytes() may return a greater value than expected even for
aligned requests.

Test Plan: make arena_test && ./arena_test

Reviewers: rven, anthony, yhchiang, aekmekji, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D46869

util/arena_test.cc

@@ -21,6 +21,14 @@ class ArenaTest : public testing::Test {};
 TEST_F(ArenaTest, Empty) { Arena arena0; }
 
 namespace {
+bool CheckMemoryAllocated(size_t allocated, size_t expected) {
+  // The value returned by Arena::MemoryAllocatedBytes() may be greater than
+  // the requested memory. We choose a somewhat arbitrary upper bound of
+  // max_expected = expected * 1.1 to detect critical overallocation.
+  size_t max_expected = expected * 1.1;
+  return allocated >= expected && allocated <= max_expected;
+}
+
 void MemoryAllocatedBytesTest(size_t huge_page_size) {
   const int N = 17;
   size_t req_sz;  // requested size
@@ -36,7 +44,8 @@ void MemoryAllocatedBytesTest(size_t huge_page_size) {
     arena.Allocate(req_sz);
   }
   expected_memory_allocated = req_sz * N + Arena::kInlineSize;
-  ASSERT_GE(arena.MemoryAllocatedBytes(), expected_memory_allocated);
+  ASSERT_PRED2(CheckMemoryAllocated, arena.MemoryAllocatedBytes(),
+               expected_memory_allocated);
 
   arena.Allocate(Arena::kInlineSize - 1);
 
@@ -49,13 +58,15 @@ void MemoryAllocatedBytesTest(size_t huge_page_size) {
     arena.Allocate(req_sz);
   }
   if (huge_page_size) {
-    ASSERT_TRUE(arena.MemoryAllocatedBytes() >=
-                    expected_memory_allocated + bsz ||
-                arena.MemoryAllocatedBytes() >=
-                    expected_memory_allocated + huge_page_size);
+    ASSERT_TRUE(
+        CheckMemoryAllocated(arena.MemoryAllocatedBytes(),
+                             expected_memory_allocated + bsz) ||
+        CheckMemoryAllocated(arena.MemoryAllocatedBytes(),
+                             expected_memory_allocated + huge_page_size));
   } else {
     expected_memory_allocated += bsz;
-    ASSERT_GE(arena.MemoryAllocatedBytes(), expected_memory_allocated);
+    ASSERT_PRED2(CheckMemoryAllocated, arena.MemoryAllocatedBytes(),
+                 expected_memory_allocated);
   }
 
   // requested size > size of a block:
@@ -66,7 +77,8 @@ void MemoryAllocatedBytesTest(size_t huge_page_size) {
     arena.Allocate(req_sz);
   }
   expected_memory_allocated += req_sz * N;
-  ASSERT_GE(arena.MemoryAllocatedBytes(), expected_memory_allocated);
+  ASSERT_PRED2(CheckMemoryAllocated, arena.MemoryAllocatedBytes(),
+               expected_memory_allocated);
 }
 
 // Make sure we didn't count the allocate but not used memory space in
@@ -83,7 +95,8 @@ static void ApproximateMemoryUsageTest(size_t huge_page_size) {
   arena.AllocateAligned(Arena::kInlineSize / 2 - 16);
   arena.AllocateAligned(Arena::kInlineSize / 2);
   ASSERT_EQ(arena.ApproximateMemoryUsage(), Arena::kInlineSize - 8);
-  ASSERT_EQ(arena.MemoryAllocatedBytes(), Arena::kInlineSize);
+  ASSERT_PRED2(CheckMemoryAllocated, arena.MemoryAllocatedBytes(),
+               Arena::kInlineSize);
 
   auto num_blocks = kBlockSize / kEntrySize;
 
@@ -91,10 +104,12 @@ static void ApproximateMemoryUsageTest(size_t huge_page_size) {
   arena.AllocateAligned(kEntrySize);
   auto mem_usage = arena.MemoryAllocatedBytes();
   if (huge_page_size) {
-    ASSERT_TRUE(mem_usage == kBlockSize + Arena::kInlineSize ||
-                mem_usage == huge_page_size + Arena::kInlineSize);
+    ASSERT_TRUE(
+        CheckMemoryAllocated(mem_usage, kBlockSize + Arena::kInlineSize) ||
+        CheckMemoryAllocated(mem_usage, huge_page_size + Arena::kInlineSize));
   } else {
-    ASSERT_EQ(mem_usage, kBlockSize + Arena::kInlineSize);
+    ASSERT_PRED2(CheckMemoryAllocated, mem_usage,
+                 kBlockSize + Arena::kInlineSize);
   }
   auto usage = arena.ApproximateMemoryUsage();
   ASSERT_LT(usage, mem_usage);