> The kernel pipe code is actually prepared for changing
> this and differentiates between PIPE_BUF and PIPE_SIZE.
> I am appending a patch against 2.3.33 that allocates
> 2 * PIPE_BUF and allows a poll for write when there
> is at least PIPE_BUF space free. Could someone please
> review it if it makes sense? - it works for me, but
> I am no kernel expert and do not know the exact semantics
> behind kernel poll routines etc.
You've just managed to make the probability of pipe creation failing raise
by a non-trivial amount because you're allocating an order 1 page instead
of order zero. I'd strongly suggest making the pipe buffers remain the
size of 1 page and allocate them dynamically. This goes towards another
pipe optimization that has been suggested: where possible, one could flip
a full page into the reader's address space rather than copying, making
for a substantial gain in pipe bandwidth.
-ben
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