"Peter.Enderborg@sony.com" Peter.Enderborg@sony.com writes:
This syscall can be used by the CRIU project and other applications which require soft-dirty PTE bit information. The following operations are supported in this syscall:
- Get the pages that are soft-dirty.
- Clear the pages which are soft-dirty.
- The optional flag to ignore the VM_SOFTDIRTY and only track per page
soft-dirty PTE bit
(For context, I wrote a previous version of this patch and have been working with Usama on the current patch).
Why can it not be done as a IOCTL?
Considering an ioctl is basically a namespaced syscall with extra-steps, surely we can do it :) There are a few reasons we haven't, though:
1) ioctl auditing/controling is much harder than syscall
2) There is a concern for performance, since this might be executed frequently by windows applications running over wine. There is an extra cost with unnecessary copy_[from/to]_user that we wanted to avoid, even though we haven't measured.
3) I originally wrote this at the time process_memadvise was merged. I felt it fits the same kind of interface exposed by process_memadvise/process_mrelease, recently merged.
4) Not obvious whether the ioctl would be against pagemap/clear_refs. Neither file name describes both input and output semantics.
Obviously, all of those reasons can be worked around, and we can turn this into an ioctl.