It is bounded by available memory. Writes to a socket go to a FIFO queue (the socket's write buffer), but writes to disk are different; they go through the pag

It is bounded by available memory. Writes to a socket go to a FIFO queue (the socket's write buffer), but writes to disk are different; they go through the page cache (https://www.kernel.org/doc/html/latest/admin-guide/mm/concepts.html https://www.kernel.org/doc/html/latest/admin-guide/mm/concep...): > The physical memory is volatile and the common case for getting data into the memory is to read it from files. Whenever a file is read, the data is put into the page cache to avoid expensive disk access on the subsequent reads. Similarly, when one writes to a file, the data is placed in the page cache and eventually gets into the backing storage device. The written pages are marked as dirty and when Linux decides to reuse them for other purposes, it makes sure to synchronize the file contents on the device with the updated data. There are many advantages to doing it this way. One is that multiple writes to the same page will result in a single physical write, if the page has not yet been flushed to disk. There are many reasons that you might have seen a write to a file block. One is that the number of dirty pages has reached the threshold (nr_dirty_threshold in /proc/vmstat). After that happens, any process doing disk IO will block. Another reason is memory pressure. Since all writes go through the page cache, the kernel must first allocate a page before the call to write(2) can be completed. If there are many pages in the page cache, this can take a long time (I once witnessed an old kernel bug cause all page allocations to result in kswapd attempting to reclaim pages, due to active pages being placed ahead of inactive pages in the LRU lists). In general, if you are writing a lot to disk but you have no intention of reading it in the near future, it is a good idea to call posix_fadvise(2) with FADV_DONTNEED to ensure the pages will be reused for something else more quickly.