Re: [PATCH v2 3/7] iomap: Remove unnecessary test from iomap_release_folio()

[Matthew Wilcox <willy@infradead.org>]

On Sun, Jun 04, 2023 at 11:01:41AM -0700, Darrick J. Wong wrote:
> On Fri, Jun 02, 2023 at 11:24:40PM +0100, Matthew Wilcox (Oracle) wrote:
> > The check for the folio being under writeback is unnecessary; the caller
> > has checked this and the folio is locked, so the folio cannot be under
> > writeback at this point.
> 
> Do we need a debug assertion here to validate that filemap_release_folio
> has already filtered out folios unergoing writeback?  The documentation
> change in the next patch might be fine since you're the pagecache
> maintainer.

I don't think so?  We don't usually include asserts in filesystems that
the VFS is living up to its promises.

> >  	/*
> > -	 * mm accommodates an old ext3 case where clean folios might
> > -	 * not have had the dirty bit cleared.  Thus, it can send actual
> > -	 * dirty folios to ->release_folio() via shrink_active_list();
> > -	 * skip those here.
> > +	 * If the folio is dirty, we refuse to release our metadata because
> > +	 * it may be partially dirty (FIXME, add a test for that).
> 
> Er... is this FIXME reflective of incomplete code?

It's a note to Ritesh ;-)

Once we have per-block dirty bits, if all the dirty bits are set, we
can free the iomap_page without losing any information.  But I don't
want to introduce a dependency between this and Ritesh's work.