Rethinking Sendfile Support in Unix Kernel

Traditional web servers, file servers, and proxies transfer files to clients using basic system calls such as UNIX’s send/writev. However, these calls incur an overhead due to copying data between user space and kernel space. This can be avoided in certain cases by utilizing UNIX’s zero-copy calls, e.g. splice and sendfile. In this paper, we suggest two simple modifications to make the use of sendfile method much more effective. We also show how we can effectively use these modifications to increase performance of existing web servers and proxies. Keywords—zero-copy, sendfile, Linux networking, TCP