Re: [PATCH 08/12] iomap: move folio_unlock out of iomap_writeback_folio

Brian Foster
2025-06-30T12:36:14Z

On Mon, Jun 30, 2025 at 07:45:42AM +0200, Christoph Hellwig wrote:
> On Fri, Jun 27, 2025 at 12:38:52PM -0400, Brian Foster wrote:
> > > Move unlocking the folio out of iomap_writeback_folio into the caller.
> > > This means the end writeback machinery is now run with the folio locked
> > > when no writeback happend, or writeback completed extremely fast.
> > >
> >
> > I notice that folio_end_dropbehind_write() (via folio_end_writeback())
> > wants to trylock the folio in order to do its thing. Is this going to
> > cause issues with that (i.e. prevent invalidations)?
>
> Good point. It renders the filemap_end_dropbehind_write call (the
> function got renamed in 6.16-rc) essentially useless. OTOH this is
> the case where no writeback happened due to a race, so it isn't needed
> to start with. But it might be worth documenting that fact.
>

I'll have to read through it again on the next round, but yeah if it's
just a calling context caveat then please do leave a note somewhere that
it's known and why it's ok. Thanks.

Brian