Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

[Christoph Hellwig]

On Wed, Aug 14, 2024 at 03:49:41PM +0800, Zhang Yi wrote:
> Sorry, this makes me confused. How does this could prevent setting
> redundant dirty bits?
> 
> Suppose we have a 3K regular file on a filesystem with 1K block size.
> In iomap_page_mkwrite(), the iter.len is 3K, if the folio size is 4K,
> folio_mark_dirty() will also mark all 4 bits of ifs dirty. And then,
> if we expand this file size to 4K, and this will still lead to a hole
> with dirty bit set but without any block allocated/reserved. Am I
> missing something?

No, we still need the ifs manipulation in the loop indeed.  But
the filemap_dirty_folio (and the not uptodate warning) can still
move outside the iterator.