Hi Kirill, > I have hard time understanding the case when new_len != old_len. > > Correct me if I'm wrong, but looks like that you change the size of old > mapping to be the new_len and then create a new of the same new_len. > > This doesn't look right to me. > > In my opinion, MREMAP_DONTUNMAP has to leave the old mapping intact. And > create the new mapping adjusted to the new_len. > > Other option is to force new_len == old_len if MREMAP_DONTUNMAP is > specified. It would simplify the implementation. And I don't see why > anybody would really want anything else. I had been approaching this as, "do what mremap would have done in this situation except skip the last step." Meaning, whatever the final state of the old mapping was MREMAP_DONTUNMAP meant that you should just not do the unmap operation on the old mapping at the end. But I understand why it's confusing, especially when in the case of the VMA growing you're left with the old vma of size old_len and the new_vma of size new_len but only containing old_len worth of pages. Personally, I don't think this is a problem having that behavior because it can be documented and it just adds a small amount of flexibility. Nonetheless, I agree with you and I also cannot come up with a situation where you'd actually want to do this so I'm willing to restrict it to old_len == new_len and return -EINVAL if not, it simplifies it a bit and accounting becomes a easier because the outcome is always the same two mappings of size old_len and the size of the locked_vm never changes. We can always allow the resize operation later if there becomes a need. If everyone is okay with this restriction I can send a new patch. Thank you again, Brian
