From: Christoph Hellwig <hch@infradead.org>
To: Qu Wenruo <wqu@suse.com>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-xfs@vger.kernel.org
Subject: Re: [PATCH] iomap: follow the alignment requirement for iomap_dio_hole_iter()
Date: Thu, 30 Jul 2026 05:01:06 -0700 [thread overview]
Message-ID: <ams9Agj_C0DhBF54@infradead.org> (raw)
In-Reply-To: <30f0bdfb-c8ee-4459-8137-773020960f7b@suse.com>
On Thu, Jul 30, 2026 at 06:06:17PM +0930, Qu Wenruo wrote:
> > iomap generall expects extents to be block aligned, how do you end up
> > with non-aligned reporting here?
>
> The dio read buffer is 2 pages (matching the 8K alignment), but only the
> first page is faulted in.
>
> Furthermore btrfs has disabled page fault during dio read, so the 2nd page
> will not be faulted in.
>
> Thus iov_iter_zero() only got to zero the first page.
>
> Btrfs always returned a hole that is properly aligned, but as long as bs >
> ps, the page fault can always break in the middle, causing unaligned range.
Urgg, we really need to get rid of this nofault behavior rather sooner
than later. But I think the iomap should always be fsblock alignment.
While we can support smaller I/O, the mapping should always be block
aligned.
prev parent reply other threads:[~2026-07-30 12:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-30 1:22 [PATCH] iomap: follow the alignment requirement for iomap_dio_hole_iter() Qu Wenruo
2026-07-30 7:45 ` Christoph Hellwig
2026-07-30 8:36 ` Qu Wenruo
2026-07-30 12:01 ` Christoph Hellwig [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ams9Agj_C0DhBF54@infradead.org \
--to=hch@infradead.org \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=wqu@suse.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox