Increased the fiber stack size to 64KB

Summary:
During the release testing (https://fburl.com/conveyor/a16yhrk4), tasks were crashing mostly by
SIGSEGV and SIGABRT. From the further analysis, it is suspected that the destructor calls from
the fiber run by the Navy's region_manager thread are causing random memory corruptions. In order to
fix this issue, this change increases the stack size of fibers used by the NavyThread to 64KB. The
increases in the stack memory usage would not be an issue for region_manager for now because the
number of fibers are bound by the number of clean regions, so the stack overhead will be bound by
the preallocated guard page stacks (100 by default); i.e., 64KB x 100 = 64MB.

Reviewed By: therealgymmy

Differential Revision: D50756161

fbshipit-source-id: 9c110504f51a2822e108571dbbf57f5d7aecb98b

cachelib/navy/common/NavyThread.h

@@ -43,12 +43,26 @@ namespace navy {
  */
 class NavyThread {
  public:
+  struct Options {
+    static constexpr size_t kDefaultStackSize{64 * 1024};
+    constexpr Options() {}
+
+    /**
+     * Maximum stack size for fibers which will be used for executing all the
+     * tasks.
+     */
+    size_t stackSize{kDefaultStackSize};
+  };
+
   /**
    * Initializes with current EventBaseManager and passed-in thread name.
    */
-  explicit NavyThread(folly::StringPiece name) {
+  explicit NavyThread(folly::StringPiece name, Options options = Options()) {
     th_ = std::make_unique<folly::ScopedEventBaseThread>(name.str());
-    fm_ = &folly::fibers::getFiberManager(*th_->getEventBase());
+
+    folly::fibers::FiberManager::Options opts;
+    opts.stackSize = options.stackSize;
+    fm_ = &folly::fibers::getFiberManager(*th_->getEventBase(), opts);
   }
 
   ~NavyThread() { th_.reset(); }