Re: [PATCH v7 16/21] block: add check when merging zone device pages

Christoph Hellwig
2022-07-04T06:07:12Z

On Thu, Jun 30, 2022 at 03:50:10PM -0600, Logan Gunthorpe wrote:
> Oh, it turns out this code has nothing to do with REQ_NOMERGE. It's used
> indirectly in bio_map_user_iov() and __bio_iov_iter_get_pages() when
> adding pages to the bio via page_is_mergeable(). So it's not about
> requests being merged it's about pages being merged.

Oh, true.

> So I'm not sure how we can avoid this, but it only happens when two
> adjacent pages are added to the same bio in a row, so I don't think it's
> that common, but the check can probably be moved down so it happens
> after the same_page check to make it a little less common.

Yes, looks like we have to keep it.