On Wed, Feb 08, 2023 at 04:09:51PM +0000, David Howells wrote:

How about one of two different solutions?

 (1) Repurpose the function I proposed for generic_file_splice_read() but only
     for splicing from O_DIRECT files; reading from non-O_DIRECT files would
     use an ITER_PIPE as upstream.

Given the amounts of problems we had with O_DIRECT vs splice, and the
fact that even doing this is a bit pointless that seems sensible to me.

     for splicing from O_DIRECT files, as (1), but also replace the splice
     from a buffered file with something like the patch below.  This uses
     filemap_get_pages() to do the reading and to get a bunch of folios from
     the pagecache that we can then splice into the pipe directly.

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.

With that in mind I'll try to find some time to review your actual
patch, but I'm a little busy at the moment.