Post Syndicated from corbet original https://lwn.net/Articles/940704/

It is the kernel’s business to know when a process’s memory has been
written to; among other things, this knowledge is needed to determine which
pages can
be immediately reclaimed or to properly write dirty pages to backing store.
Sometimes, though, user space also needs access to this information in a
reliable and fast manner. This
patch series from Muhammad Usama Anjum adds a new ioctl() call
for this purpose; using it requires repurposing an existing system call in
an unusual way, though.