On 4/30/09 8:35 , "Pavel Shamis (Pasha)" <[email protected]> wrote:
> Barrett, Brian W wrote: >> Jeff and I talked for a while today, and we're pretty sure that as long as >> the byte set by the kernel notifier is written before the pages are returned >> into the unallocated list, there isn't actually a race condition. It does >> mean that every time the page cache is searched, we also have to check the >> byte (and likely take a cache miss), but that's not too evil. >> >> However, there's still then the problem with the notifier concept of how the >> kernel passes which pages were given back to the kernel. It has to pass a >> (potentially very large) amount of data back to the user, so the memory >> ownership issues with kernel/user space are interesting. It also has to >> somewhat atomically prepare the list and undset the notifier byte, which is >> also problematic. But probably workable. >> > It sounds like we will have another 5k lines of code in MPI that will > try to resolve > the kernel/user notification issue :-) > IMHO, Lets avoid all these tricks and move the registration cache to kernel. I don't disagree - this is a problem best solved in kernel space, preferably using the approach Jeff originally proposed. I think the complexity of handling notifier callback will be fairly high, but it is still an improvement over where we are today. Today's user-space memory hooks need to go - they cause too many problems for both the MPI and the application. Brian -- Brian W. Barrett Dept. 1423: Scalable System Software Sandia National Laboratories _______________________________________________ general mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
