On Thu, Mar 5, 2015 at 9:18 AM, Andrea Arcangeli <aarca...@redhat.com> wrote: > remap_pages is the lowlevel mm helper needed to implement > UFFDIO_REMAP.
This function is nasty nasty nasty. Is this really worth it? On real loads? That people are expected to use? Considering how we just got rid of one special magic VM remapping thing that nobody actually used, I'd really hate to add a new one. The fact is, almost nobody ever uses anything that isn't standard POSIX. There are no apps, and even for specialized things like virtualization hypervisors this kind of thing is often simply not worth it. Quite frankly, *if* we ever merge userfaultfd, I would *strongly* argue for not merging the remap parts. I just don't see the point. It doesn't seem to add anything that is semantically very important - it's *potentially* a faster copy, but even that is (a) questionable in the first place and (b) unclear why anybody would ever care about performance of infrastructure that nobody actually uses today, and future use isn't even clear or shown to be particualrly performance-sensitive. So basically I'd like to see better documentation, a few real use cases (and by real I very much do *not* mean "you can use it for this", but actual patches to actual projects that matter and that are expected to care and merge them), and a simplified series that doesn't do the remap thing. Because *every* time we add a new clever interface, we end up with approximately zero users and just pain down the line. Examples: splice, mremap, yadda yadda. Linus -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html