Re: 2.6.11-rc1-mm1

[Karim Yaghmour <karim@opersys.com>]

Karim Yaghmour wrote:
> This is not good for any client that doesn't know beforehand the exact
> size of their data units, as in the case of LTT. If LTT has to use this
> code that means we are going to loose performance because we will need to
> fill an intermediate data structure which will only be used for relay_write().
> Instead of zero-copy, we would have an extra unnecessary copy. There has
> got to be a way for clients to directly reserve and write as they wish.
> Even Zach Brown recognized this in his tracepipe proposal, here's from
> his patch:
> + * 	- let caller reserve space and get a pointer into buf

Actually, come to think of it, this code is not good for any client that
needs to fill complex data structures, whether they be fixed-size or not,
because it requires having a prepackaged structure already available.
Any client that wants to have zero-copying will want to write data
directly into the buffer instead of filling an intermediate buffer first.
And this requires being able to atomically reserve.

Karim
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