Jeff Smith wrote: > 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).
Em.. What's wrong with shm_open() + two mmap()s to cover both halfs? fd = shm_open(); addr1 = mmap(NULL, 2*SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); addr2 = mmap(addr1 + SIZE, PROT_READ|PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, 0); Is there a reason why it doens't work? > 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 I believe remap_file_pages() is abused here. But it seems we will have to keep emulation in place for a long time. > > 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. I don't get this part. -- Kirill A. Shutemov -- 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/
