Linux: What Can You Epoll?
&gt; On Linux write to a regular file never blocks. Writing to a file copies data from our user space buffer to the kernel buffer and returns immediately. At some later point in time the kernel will send it to the disk. A regular file is hence always ready for writing and epoll wouldn’t add anything.<p>Is that true? If it would be, the amount of data the Kernel would need to buffer is unbounded. I assumed there is a limit on the amount of buffered and not yet committed data, and when that is cross the call would block until more data is flushed to disk. Which is kind of the same as happens for TCP sockets. The `write()` call there doesn&#x27;t really send data to the peer, it just submits data to the kernels send buffer, from where it will be asynchronously transmitted.<p>Edit: Actually I will answer my own question and say I know it will block. I had deployed IO heavy applications in the past with instrumented read&#x2F;write calls for IO operations in a threadpool. Even though typical IO times are well below 1ms, under extremely high load latencies of more than 1s could be observed, which is far from &quot;not blocking&quot;.