> * Steven Rostedt (
rostedt@goodmis.org) wrote:
> > On Wed, 2010-05-19 at 17:33 +0200, Miklos Szeredi wrote:
> > > On Wed, 19 May 2010, Linus Torvalds wrote:
> > > > Btw, since you apparently have a real case - is the "splice to file"
> > > > always just an append? IOW, if I'm not right in assuming that the only
> > > > sane thing people would reasonable care about is "append to a file", then
> > > > holler now.
> > >
> > > Virtual machines might reasonably need this for splicing to a disk
> > > image.
> >
> > This comes down to balancing speed and complexity. Perhaps a copy is
> > fine in this case.
> >
> > I'm concerned about high speed tracing, where we are always just taking
> > pages from the trace ring buffer and appending them to a file or sending
> > them off to the network. The slower this is, the more likely you will
> > lose events.
> >
> > If the "move only on append to file" is easy to implement, I would
> > really like to see that happen. The speed of splicing a disk image for a
> > virtual machine only impacts the patience of the user. The speed of
> > splicing tracing output, impacts how much you can trace without losing
> > events.
>
> I'm with Steven here. I only care about appending full pages at the end of a
> file. If possible, I'd also like to steal back the pages after waiting for the
> writeback I/O to complete so we can put them back in the ring buffer without
> stressing the page cache and the page allocator needlessly.
