Move hardcoded asan multiplier to a config

Summary: This export the 16 times stack size for ASAN TSAN into a config as @[655434592:Andrii Grynenko] suggested

Reviewed By: yfeldblum

Differential Revision: D9685364

fbshipit-source-id: 4c76e99ba10d0fad65dd0dc30eeb003b25514c43

folly/fibers/FiberManagerInternal-inl.h

@@ -37,13 +37,11 @@ namespace fibers {
 namespace {
 
 inline FiberManager::Options preprocessOptions(FiberManager::Options opts) {
-#if defined(FOLLY_SANITIZE_ADDRESS) || defined(FOLLY_SANITIZE_THREAD)
-  /* Sanitizers need a lot of extra stack space.
-     16x is a conservative estimate, 8x also worked with tests
-     where it mattered.  Note that overallocating here does not necessarily
-     increase RSS, since unused memory is pretty much free. */
-  opts.stackSize *= 16;
-#endif
+  /**
+   * Adjust the stack size according to the multiplier config.
+   * Typically used with sanitizers, which need a lot of extra stack space.
+   */
+  opts.stackSize *= std::exchange(opts.stackSizeMultiplier, 1);
   return opts;
 }
 

folly/fibers/FiberManagerInternal.h

@@ -85,6 +85,14 @@ class FiberManager : public ::folly::Executor {
      */
     size_t stackSize{kDefaultStackSize};
 
+    /**
+     * Sanitizers need a lot of extra stack space. 16x is a conservative
+     * estimate, but 8x also worked with tests where it mattered. Note that
+     * over-allocating here does not necessarily increase RSS, since unused
+     * memory is pretty much free.
+     */
+    size_t stackSizeMultiplier{kIsSanitize ? 16 : 1};
+
     /**
      * Record exact amount of stack used.
      *