Enable hot static code mapping onto huge pages

This diff enables mapping of hot static code onto huge pages for open
source builds. It defines __hot_start and __hot_end at link time using
the first and last functions from the linker script. This feature can be
turned off by setting the CMake option MAP_TEXT_HUGE_PAGES to 'Off'.

hugifyText was aligned to 2MB so that we maximize the amount of hot code
we can map if __hot_end is placed just before it.

Solves facebook#5269

CMake/Options.cmake

@@ -34,6 +34,10 @@ option(ENABLE_PROXYGEN_SERVER "Build the Proxygen HTTP server" ON)
 
 option(ENABLE_SPLIT_DWARF "Reduce linker memory usage by putting debugging information into .dwo files" OFF)
 
+IF (LINUX)
+    option(MAP_TEXT_HUGE_PAGES "Remap hot static code onto huge pages" ON)
+ENDIF()
+
 IF (NOT DEFAULT_CONFIG_DIR)
   set(DEFAULT_CONFIG_DIR "/etc/hhvm/" CACHE STRING
     "Default directory to find php.ini")

hphp/hhvm/CMakeLists.txt

@@ -11,6 +11,17 @@ endif()
 
 option(ENABLE_LD_GOLD "Enable Hot Linker script using ld-gold" On)
 set(SECTION_ORDERING_FILE ${CMAKE_CURRENT_SOURCE_DIR}/../tools/oss_hot_section_ordering CACHE FILEPATH "File used by ld-gold for the relocation of sections")
+
+if (MAP_TEXT_HUGE_PAGES)
+    file(STRINGS "${SECTION_ORDERING_FILE}" SECTION_ORDERING_CONTENTS)
+    list(GET SECTION_ORDERING_CONTENTS 0 HOT_START)
+    list(GET SECTION_ORDERING_CONTENTS -1 HOT_END)
+    string(REGEX REPLACE "\\.text\\.(.*)\\*" "\\1" HOT_START ${HOT_START})
+    string(REGEX REPLACE "\\.text\\.(.*)\\*" "\\1" HOT_END ${HOT_END})
+    set(DEFSYM_HOT_START "--defsym=__hot_start=${HOT_START},")
+    set(DEFSYM_HOT_END "--defsym=__hot_end=${HOT_END},")
+endif()
+
 if (ENABLE_LD_GOLD)
   find_package(Gold)
 endif()
@@ -21,9 +32,9 @@ target_link_libraries(hhvm ${HHVM_LINK_LIBRARIES} ${EZC_LINK_LIBRARIES} ${HRE_LI
 link_object_libraries(hhvm ${HHVM_WHOLE_ARCHIVE_LIBRARIES})
 if (GOLD_FOUND AND ENABLE_LD_GOLD)
   if (CMAKE_CONFIGURATION_TYPES)
-    SET(LINKER_SCRIPT -fuse-ld=gold;-Wl,--icf=all,--gc-sections;release;-Wl,--section-ordering-file,${SECTION_ORDERING_FILE};default)
+    SET(LINKER_SCRIPT -fuse-ld=gold;-Wl,--icf=all,--gc-sections;release;-Wl,${DEFSYM_HOT_START}${DEFSYM_HOT_END}--section-ordering-file,${SECTION_ORDERING_FILE};default)
   elseif(NOT CMAKE_BUILD_TYPE MATCHES "Debug")
-    SET(LINKER_SCRIPT -fuse-ld=gold -Wl,--section-ordering-file,${SECTION_ORDERING_FILE},--icf=all,--gc-sections)
+    SET(LINKER_SCRIPT -fuse-ld=gold -Wl,${DEFSYM_HOT_START}${DEFSYM_HOT_END}--section-ordering-file,${SECTION_ORDERING_FILE},--icf=all,--gc-sections)
   else()
     SET(LINKER_SCRIPT -fuse-ld=gold -Wl,--icf=all,--gc-sections)
   endif()

hphp/runtime/base/program-functions.cpp

@@ -755,16 +755,12 @@ void execute_command_line_end(int xhprof, bool coverage, const char *program) {
 const void* __hot_start = nullptr;
 const void* __hot_end = nullptr;
 #endif
-
-#if FACEBOOK
 # define AT_END_OF_TEXT       __attribute__((__section__(".stub")))
-#else
-# define AT_END_OF_TEXT
-#endif
+# define ALIGN_HUGE_PAGE      __attribute__((aligned(2 * 1024 * 1024)))
 
-static void NEVER_INLINE AT_END_OF_TEXT __attribute__((__optimize__("2")))
+static void NEVER_INLINE AT_END_OF_TEXT ALIGN_HUGE_PAGE __attribute__((__optimize__("2")))
 hugifyText(char* from, char* to) {
-#if FACEBOOK && !defined FOLLY_SANITIZE_ADDRESS && defined MADV_HUGEPAGE
+#if !defined FOLLY_SANITIZE_ADDRESS && defined MADV_HUGEPAGE
   if (from > to || (to - from) < sizeof(uint64_t)) {
     // This shouldn't happen if HHVM is behaving correctly (I think),
     // but if it does then there is nothing to do and we should bail
@@ -796,6 +792,10 @@ hugifyText(char* from, char* to) {
   free(mem);
   mlock(from, to - from);
   Debug::DebugInfo::setPidMapOverlay(from, to);
+  std::stringstream ss;
+  ss << "Mapped text section onto huge pages from " <<
+      std::hex << (uint64_t*)from << " to " << (uint64_t*)to;
+  Logger::Info(ss.str());
 #endif
 }
 
@@ -854,7 +854,7 @@ static void pagein_self(void) {
           if (to - from >  maxHugeHotTextBytes) {
             to = from + maxHugeHotTextBytes;
           }
-          if (to < (void*)hugifyText) {
+          if (to <= (void*)hugifyText) {
             hugifyText(from, to);
           }
         }