Re: [PATCH 2/7] mm: stop passing a writeback_control structure to shmem_writeout

Christoph Hellwig
2025-05-08T14:03:31Z

On Thu, May 08, 2025 at 02:25:00PM +0100, Matthew Wilcox wrote:
> This got me to look at why we need to keep wbc in __shmem_writeback().
> We only have it because folio_redirty_for_writepage() needs it. And
> folio_redirty_for_writepage() only needs it because it updates
> pages_skipped.

in linux-next you also changed it to use writeback_iter, which needs
the wbc as well. That probably as an improvement compared to the
previous version, but overall it still feels odd.

> I'm not quite sure if we can simply call filemap_dirty_folio() here
> or whether mapping_can_writeback() is true for shmem and we need to
> do all the other things -- in which case we could just change that one
> line to

shmem doesn't set up a bdi, so it should not be true.