I might have expressed myself somewhat unclear. Let me try again. varnishd tries to write to a page not in memory and gets a page fault while doing so. As the k

I might have expressed myself somewhat unclear. Let me try again. varnishd tries to write to a page not in memory and gets a page fault while doing so. As the kernel has no idea of your intentions to overwrite the whole page it will read the page into memory and then return control to varnish who completes the memory write, merging the write request just made onto the preexisting page. varnish does not utilize any asynchronous reads. All IO is blocking.