On Mon, May 19, 2014 at 9:38 AM, Christoph Hellwig <h...@infradead.org> wrote: > On Mon, May 19, 2014 at 05:35:40PM +0300, Kirill A. Shutemov wrote: >> >From functional POV, emulation *should* be identical to original >> remap_file_pages(), but slower. It would be nice, if you test it early. >> >> It's not clear yet how long emulation will be there. > > Stop right there. We found out about two real life users of > remap_file_pages() already, without even committing the patches to warn > about using it to any tree. > > I think at this point the whole idea of removing the API should be dead > on the floor, as we do not needlessly break userspace programs. > > If we can get rid of the ugly guts and provide a good enough emulation > that the user won't cry I'd love to get rid of this cruft, but even > that doesn't look certain yet.
Sorry for being late to the party, but I just noticed this proposal via the LWN summary byline. I wanted to comment that Kenny's use case is (I believe) quite widespread. I've used the technique since ~2008, and I've come across other people in subsequent jobs who independently developed the same technique. Mirrored mapping is absolutely required by several independent proprietary platforms I'm aware of, and remap_file_pages() has historically been the only sane way to accomplish this. (i.e., shm_open(), mmap(NULL, 2^(n+1) pages), remap_file_pages() on 2nd half). It may not be individuals who are involved in the kernel development scene to any great extent, but I am sure that remap_file_pages() being deprecated would seriously piss off a lot of individuals. The pattern has even had a section in the Wikipedia article for quite some time: http://en.wikipedia.org/wiki/Circular_buffer#Mirroring It would be most preferable from a user standpoint to keep the existing system intact, but failing that, a reservation API would need to be created (possibly a MAP_RESERVE flag) that would set aside a region that could only be subsequently mapped via explicit address-requesting mmap() calls. Thanks for any consideration of these concerns. --Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
