Re: [PLEASE-TESTME] Zerocopy networking patch, 2.4.0-1

[Ingo Molnar]

On Tue, 9 Jan 2001, Dave Zarzycki wrote:

> In user space, how do you know when its safe to reuse the buffer that
> was handed to sendmsg() with the MSG_NOCOPY flag? Or does sendmsg()
> with that flag block until the buffer isn't needed by the kernel any
> more? If it does block, doesn't that defeat the use of non-blocking
> I/O?

sendmsg() marks those pages COW and copies the original page into a new
one for further usage. (the old page is used until the packet is
released.) So for maximum performance user-space should not reuse such
buffers immediately.

        Ingo

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