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Date:   Mon, 4 Jul 2022 08:07:00 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
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        Stephen Bates <sbates@raithlin.com>,
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        Ralph Campbell <rcampbell@nvidia.com>
Subject: Re: [PATCH v7 16/21] block: add check when merging zone device
 pages
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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.