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) -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- 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>