io_liburing: ENOMEM handling - use io_uring_mlock_size

This gives the user the size required and how to set
memlock limits for the process.

Thanks Jens Axboe for providing this requested interface

ref: https://github.com/axboe/liburing/issues/246

Also don't put \n on my_printf_error, its implicit.

tpool/CMakeLists.txt

@@ -17,6 +17,16 @@ ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     LINK_LIBRARIES(${URING_LIBRARIES})
     INCLUDE_DIRECTORIES(${URING_INCLUDE_DIR})
     SET(EXTRA_SOURCES aio_liburing.cc)
+    SET(CMAKE_REQUIRED_INCLUDES_SAVE ${CMAKE_REQUIRED_INCLUDES})
+    SET(CMAKE_REQUIRED_LIBRARIES_SAVE ${CMAKE_REQUIRED_LIBRARIES})
+    SET(CMAKE_REQUIRED_INCLUDES ${URING_INCLUDE_DIR})
+    SET(CMAKE_REQUIRED_LIBRARIES ${URING_LIBRARIES})
+    CHECK_SYMBOL_EXISTS(io_uring_mlock_size "liburing.h" HAVE_IO_URING_MLOCK_SIZE)
+    SET(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES_SAVE})
+    SET(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_SAVE})
+    IF(HAVE_IO_URING_MLOCK_SIZE)
+      SET_SOURCE_FILES_PROPERTIES(aio_liburing.cc PROPERTIES COMPILE_FLAGS "-DHAVE_IO_URING_MLOCK_SIZE")
+    ENDIF()
   ELSE()
     FIND_PACKAGE(LIBAIO QUIET ${LIBAIO_REQUIRED})
     IF(LIBAIO_FOUND)

tpool/aio_liburing.cc

@@ -37,17 +37,27 @@ class aio_uring final : public tpool::aio
     {
       switch (const auto e= errno) {
       case ENOMEM:
+        my_printf_error(ER_UNKNOWN_ERROR,
+                        "io_uring_queue_init() failed with ENOMEM:"
+                        " try larger memory locked limit, ulimit -l"
+                        ", or https://mariadb.com/kb/en/systemd/#configuring-limitmemlock"
+                        " under systemd"
+#ifdef HAVE_IO_URING_MLOCK_SIZE
+                        " (%zd bytes required)", ME_ERROR_LOG | ME_WARNING,
+                        io_uring_mlock_size(max_aio, 0));
+#else
+                        , ME_ERROR_LOG | ME_WARNING);
+#endif
+        break;
       case ENOSYS:
-        my_printf_error(ER_UNKNOWN_ERROR, e == ENOMEM
-                        ? "io_uring_queue_init() failed with ENOMEM:"
-                        " try larger ulimit -l\n"
-                        : "io_uring_queue_init() failed with ENOSYS:"
-                        " try uprading the kernel\n",
+        my_printf_error(ER_UNKNOWN_ERROR,
+                        "io_uring_queue_init() failed with ENOSYS:"
+                        " try uprading the kernel",
                         ME_ERROR_LOG | ME_WARNING);
         break;
       default:
         my_printf_error(ER_UNKNOWN_ERROR,
-                        "io_uring_queue_init() failed with errno %d\n",
+                        "io_uring_queue_init() failed with errno %d",
                         ME_ERROR_LOG | ME_WARNING, e);
       }
       throw std::runtime_error("aio_uring()");