Re: [PATCH 09/12] iomap: lift the xfs writeback code to iomap

[Christoph Hellwig]

On Wed, Oct 16, 2019 at 09:07:21AM +1100, Dave Chinner wrote:
> > +/*
> > + * We implement an immediate ioend submission policy here to avoid needing to
> > + * chain multiple ioends and hence nest mempool allocations which can violate
> > + * forward progress guarantees we need to provide. The current ioend we are
> > + * adding blocks to is cached on the writepage context, and if the new block
> 
> adding pages to ... , and if the new block mapping

So reviewing this comment I disagree with the change.  We add on a per-
block basis to the ioend, not a per-page one.  Similar for the second 
one it is the block that needs to append (which is defined by the
mapping, but still..).