READ_PLUS in NetFS? Re: [PATCH v10 30/35] netfs: Simplify read abandonment

On Mon, Aug 24, 2026 at 5:04 PM David Howells <[email protected]> wrote:
>
> Currently, if one or more of the subrequests in a read request fails, the
> read collection algorithm will attempt to salvage folios that are fully
> downloaded but that span multiple subreqs, provided all of the contributory
> subreqs succeeded, but this makes the algorithm quite complicated as a
> subreq can contribute to multiple folios and a folio can be contributed to
> by multiple subreqs.
>
> Simplify this by just abandoning the rest of a read request once a
> permanently failed subreq is hit.  This is what read_folio, DIO/unbuffered
> read, gap filling, RMW and write preload all need to do; readahead is the
> odd one out as it doesn't have any return other than unlocking folios.
>
> With this change, even for readahead, the rest of the read is simply
> abandoned; read() and suchlike will call ->read_folio() on each
> non-uptodate folio to retry and retrieve the error.
>
> Note that retryable failures still get retried by netfslib as part of the
> request as before.

What about READ_PLUS, i.e. sparse file reads? If you do this kind of
work of handling partial abandonment, can such a work also benefit
READ_PLUS?

Aurélien
-- 
Aurélien Couderc <[email protected]>
Big Data/Data mining expert, chess enthusiast