Re: [PATCH] sendfile removal

[Fengguang Wu <fengguang.wu@gmail.com>]

On Mon, Jun 04, 2007 at 10:05:35AM +0200, Jens Axboe wrote:
> On Mon, Jun 04 2007, Fengguang Wu wrote:
> > Hi Jens,
> > 
> > This is another try, still not in a comfortable state though.
> > //Busy waiting is possible for interleaved reads.
> 
> A few random comments...
> 
> Adding an internal flag is fine, but please put it at the upper end of
> the spectrum. So, use (1 << 31) for that flag.

OK.

> And please work on the #splice branch of the block repo, not -mm. There
> are quite a few things pending for inclusion in there, and I'm sure your
> patch as-is wont apply.

I'm afraid this patch cannot be moved over to your branch trivially.

The core of the algorithm reuses f_ra.prev_index to record the state.
It is OK for the on-demand readahead in the -mm tree. But the current
readahead code in 2.6.22-rc3 is sensible to the change. And it also
does not reliably tell if readahead I/O has been submitted.

We can either try other ways of doing non-blocking I/O, or just wait
until the merge of on-demand readahead?

The current patch should work perfect with single splice reader. In
the case of multiple readers on the same fd, we might simply err on
the side of I/O waiting, since busy EAGAIN looping is not acceptable.

Fengguang Wu