* Avi Kivity <avi@xxxxxxxxxx> wrote: > On 09/15/2010 03:18 AM, Christopher Yeoh wrote: > > > The basic idea behind cross memory attach is to allow MPI programs > > doing intra-node communication to do a single copy of the message > > rather than a double copy of the message via shared memory. > > If the host has a dma engine (many modern ones do) you can reduce this > to zero copies (at least, zero processor copies). > > > The following patch attempts to achieve this by allowing a > > destination process, given an address and size from a source > > process, to copy memory directly from the source process into its > > own address space via a system call. There is also a symmetrical > > ability to copy from the current process's address space into a > > destination process's address space. > > Instead of those two syscalls, how about a vmfd(pid_t pid, ulong > start, ulong len) system call which returns an file descriptor that > represents a portion of the process address space. You can then use > preadv() and pwritev() to copy memory, and io_submit(IO_CMD_PREADV) > and io_submit(IO_CMD_PWRITEV) for asynchronous variants (especially > useful with a dma engine, since that adds latency). > > With some care (and use of mmu_notifiers) you can even mmap() your > vmfd and access remote process memory directly. > > A nice property of file descriptors is that you can pass them around > securely via SCM_RIGHTS. So a process can create a window into its > address space and pass it to other processes. > > (or you could just use a shared memory object and pass it around) Interesting, but how will that work in a scalable way with lots of non-thread tasks? Say we have 100 processes. We'd have to have 100 fd's - each has to be passed to a new worker process. In that sense a PID is just as good of a reference as an fd - it can be looked up lockless, etc. - but has the added advantage that it can be passed along just by number. Thanks, Ingo -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>