Re: [RFC PATCH V3] iomap: add support to track dirty state of sub pages

[Christoph Hellwig]

On Thu, Aug 20, 2020 at 09:38:53AM +0800, yukuai (C) wrote:
> > > +iomap_set_range_dirty(struct page *page, unsigned int off,
> > > +		unsigned int len)
> > > +{
> > > +	if (PageError(page))
> > > +		return;
> > > +
> > > +	if (page_has_private(page))
> > > +		iomap_iop_set_range_dirty(page, off, len);
> > 
> > 
> > I vaguely remembered iomap doesn't always set up PagePrivate.
> > 
> 
> If so, maybe I should move iomap_set_page_dirty() to
> ioamp_set_range_dirty().

iomap sets PagePrivate if a iomap_page structure is allocated.  Right
now that means for all pages on a file system with a block size smaller
than the page size, although I hope we reduce that scope a little.