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]
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