On Mon, Sep 15, 2008 at 02:44:32PM +0800, Lin Mac wrote: > > I think my question is not precise. And I'm not really familiar with linux > block and virtual file system subsystems, so please correct me if I'm wrong.
Neither am I :-). > Reading from samba can achieve zero copy with help of sendfile and > scather/gather support of NIC driver. > > Writing to samba by going to user space and back again would cause 2 memory > copy (copy_to_user, copy_from_user). > > Writing to samba with splice could avoid going to user space, so there is no > memory copy (copy_to_user, copy_from_user). But buffers received from network > driver (around 1.5kB each) are sent to file system subsystem and below. Will > it be cached and gathered to become a continuous buffer (which cause 1 memory > copy), or does virtual file system subsystem and below could support > scatter/gather, so there will be no memory copy at all (zero copy) ? This is a kernel implementation detail. Remember Samba runs on many other kernels, not just Linux. Linux has splice, *BSD has receivefile, Solaris probably has something different. The point is that Samba calls the kernel function at the right point to *allow* zero-copy writes - it's up to the specific kernel to ensure that happens (this is a long-winded way of saying I'm not a kernel engineer, sorry :-). Jeremy. -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/listinfo/samba
