Enable 64B spans by default.

This enables spans that are cacheline aligned. PiperOrigin-RevId: 702797456 Change-Id: Ic779740b07058fecb9ed6d05f2b756396b4f9992
google · Dec 4, 2024 · c42319e · c42319e
1 parent fcc9101
commit c42319e
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Showing 3 changed files with 17 additions and 8 deletions.
diff --git a/tcmalloc/span_test.cc b/tcmalloc/span_test.cc
@@ -268,10 +268,12 @@ TEST(SpanAllocatorTest, Alignment) {
                             ABSL_CACHELINE_SIZE];
   }
 
-  // Not all spans are currently aligned to a cacheline.
-  //
-  // TODO(b/304135905): Modify this assumption.
-  EXPECT_LT(address_mod_cacheline[0], kNumSpans);
+  // TODO(b/304135905): Remove the opt out.
+  if (tcmalloc_big_span()) {
+    EXPECT_EQ(address_mod_cacheline[0], kNumSpans);
+  } else {
+    EXPECT_LT(address_mod_cacheline[0], kNumSpans);
+  }
 
   // Verify alignof is respected.
   for (auto [alignment, count] : address_mod_cacheline) {

diff --git a/tcmalloc/static_vars.cc b/tcmalloc/static_vars.cc
@@ -61,6 +61,7 @@ GOOGLE_MALLOC_SECTION_BEGIN
 namespace tcmalloc {
 namespace tcmalloc_internal {
 
+// TODO(b/304135905): Remove the opt out.
 ABSL_ATTRIBUTE_WEAK bool default_want_disable_tcmalloc_big_span();
 bool tcmalloc_big_span() {
   // Disable 64B span if built against an opt-out.
@@ -72,8 +73,7 @@ bool tcmalloc_big_span() {
   if (e) {
     switch (e[0]) {
       case '0':
-        // TODO(b/304135905): Enable this.
-        return false;
+        return true;
       case '1':
         return false;
       default:
@@ -82,8 +82,7 @@ bool tcmalloc_big_span() {
     }
   }
 
-  // TODO(b/304135905): Enable this by default.
-  return false;
+  return true;
 }
 
 // Cacheline-align our SizeMap and CpuCache.  They both have very hot arrays as

diff --git a/tcmalloc/variants.bzl b/tcmalloc/variants.bzl
@@ -141,6 +141,14 @@ test_variants = [
         "copts": ["-DTCMALLOC_INTERNAL_256K_PAGES", "-DTCMALLOC_INTERNAL_NUMA_AWARE"],
         "tags": ["noubsan"],
     },
+    {
+        "name": "big_span_disable",
+        "malloc": "//tcmalloc",
+        "deps": [
+            "//tcmalloc:common_8k_pages",
+        ],
+        "env": {"TCMALLOC_DISABLE_BIG_SPAN": "1"},
+    },
     {
         "name": "256k_pages_pow2_sharded_transfer_cache",
         "malloc": "//tcmalloc:tcmalloc_256k_pages",