MDEV-32268: GNU libc posix_fallocate() may be extremely slow

os_file_set_size(): Let us invoke the Linux system call fallocate(2)
directly, because the GNU libc posix_fallocate() implements a fallback
that writes to the file 1 byte every 4096 or fewer bytes. In one
environment, invoking fallocate() directly would lead to 4 times the
file growth rate during ALTER TABLE. Presumably, what happened was
that the NFS server used a smaller allocation block size than 4096 bytes
and therefore created a heavily fragmented sparse file when
posix_fallocate() was used. For example, extending a file by 4 MiB
would create 1,024 file fragments. When the file is actually being
written to with data, it would be "unsparsed".

The built-in EOPNOTSUPP fallback in os_file_set_size() writes a buffer
of 1 MiB of NUL bytes. This was always used on musl libc and other
Linux implementations of posix_fallocate().

storage/innobase/os/os0file.cc

@@ -4934,8 +4934,18 @@ os_file_set_size(
 				return true;
 			}
 			current_size &= ~4095ULL;
+#  ifdef __linux__
+			if (!fallocate(file, 0, current_size,
+				       size - current_size)) {
+				err = 0;
+				break;
+			}
+
+			err = errno;
+#  else
 			err = posix_fallocate(file, current_size,
 					      size - current_size);
+#  endif
 		}
 	} while (err == EINTR
 		 && srv_shutdown_state <= SRV_SHUTDOWN_INITIATED);