On Fri, Jul 3, 2020 at 1:41 PM Matthew Wilcox <wi...@infradead.org> wrote: > > On Fri, Jul 03, 2020 at 11:53:24AM +0200, Andreas Gruenbacher wrote: > > Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it > > shouldn't trigger any filesystem I/O for the actual request or for > > readahead. This allows to do tentative reads out of the page cache as > > some filesystems allow, and to take the appropriate locks and retry the > > reads only if the requested pages are not cached. > > > > Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com> > > Reviewed-by: Matthew Wilcox (Oracle) <wi...@infradead.org> > > > @@ -2249,9 +2253,18 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read); > > * > > * This is the "read_iter()" routine for all filesystems > > * that can use the page cache directly. > > + * > > + * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall > > + * be returned when no data can be read without waiting for I/O requests > > + * to complete; it doesn't prevent readahead. > > + * > > + * The IOCB_NOIO flag in iocb->ki_flags indicates that -EAGAIN shall be > > + * returned when no data can be read without issuing new I/O requests, > > + * and 0 shall be returned when readhead would have been triggered. > > s/shall/may/ -- if we read a previous page then hit a readahead page, > we'll return a positive value. If the first page we hit is a readahead > page, then yes, we'll return zero.
How about this? * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O * requests shall be made for the read or for readahead. When no data * can be read, -EAGAIN shall be returned. When readahead would be * triggered, a short read (possibly of length 0) shall be returned. > Again, I'm happy for the patch to go in as-is without this nitpick. Thanks, Andreas
