On Thu, 17 Mar 2011 12:54:27 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, 17 Mar 2011 15:40:26 +1030 > Christopher Yeoh <cyeoh@xxxxxxxxxxx> wrote: > > > > Thinking out loud: if we had a way in which a process can add and > > > remove a local anonymous page into pagecache then other processes > > > could access that page via mmap. If both processes map the file > > > with a nonlinear vma they they can happily sit there flipping > > > pages into and out of the shared mmap at arbitrary file offsets. > > > The details might get hairy ;) We wouldn't want all the regular > > > mmap semantics of > > > > Yea, its the complexity of trying to do it that way that eventually > > lead me to implementing it via a syscall and get_user_pages > > instead, trying to keep things as simple as possible. > > The pagecache trick potentially gives zero-copy access, whereas the > proposed code is single-copy. Although the expected benefits of that > may not be so great due to TLB manipulation overheads. > > I worry that one day someone will come along and implement the > pagecache trick, then we're stuck with obsolete code which we have to > maintain for ever. Perhaps I don't understand what you're saying correctly but I think that one problem with the zero copy page flipping approach is that there is no guarantee with the data that the MPI apps want to send resides in a page or pages all by itself. Regards, Chris -- cyeoh@xxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>