Christoph Hellwig [off-list ref] wrote:

I defintively like the idea of killing ITER_PIPE.  Isn't the 16
folios in a folio tree often much less than what we could fit into
a single pipe buf?  Unless you have a file system that can use
huge folios for buffered I/O and actually does this might significantly
limit performance.

There's a loop there that repeats the filemap_get_pages() until either the
pipe is full or we hit EOF, the same as in filemap_read() (upon which this is
based).

I want to use filemap_get_pages() if I can as that does all the readahead
stuff.  What might be nice, though, is if I could tell it to return rather
than waiting for a folio to come uptodate if it has already returned a folio
so that I can push the other side of the splice along whilst the read is in
progress.

David