Darrick,

On Tue, Jun 29, 2021 at 7:47 AM Christoph Hellwig [off-list ref] wrote:

On Mon, Jun 28, 2021 at 10:59:55PM +0100, Matthew Wilcox wrote:

quoted

quoted

quoted

so permit pages without an iop to enter writeback and create an iop
*then*.  Would that solve your problem?

It is the right thing to do, especially when combined with a feature
patch to not bother to create the iomap_page structure on small
block size file systems when the extent covers the whole page.

We don't know the extent layout at the point where *this* patch creates
iomap_pages during writeback.  I imagine we can delay creating one until
we find out what our destination layout will be?

Hmm.  Actually ->page_mkwrite is always is always called on an uptodate
page and we even assert that.  I should have remembered the whole page
fault path better.

So yeah, I think we should take patch 1 from Andreas, then a non-folio
version of your patch as a start.

will you pick up those two patches and push them to Linus? They both
seem pretty safe.

Thanks,
Andreas