Message-ID: <5706ae6d-5ffd-445d-bfb3-d44fc2afa350@189.cn>
Date: Wed, 20 Aug 2025 09:52:36 +0800
From: Song Chen <chensong_2000@....cn>
To: Keith Busch <kbusch@...a.com>, linux-block@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: snitzer@...nel.org, axboe@...nel.dk, dw@...idwei.uk, brauner@...nel.org,
 hch@....de, martin.petersen@...cle.com, djwong@...nel.org,
 linux-xfs@...r.kernel.org, viro@...iv.linux.org.uk,
 Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCHv3 0/8] direct-io: even more flexible io vectors

Hi,

在 2025/8/20 00:49, Keith Busch 写道:
> From: Keith Busch <kbusch@...nel.org>
> 
> Previous version:
> 
>    https://lore.kernel.org/linux-block/20250805141123.332298-1-kbusch@meta.com/
> 
> This series removes the direct io requirement that io vector lengths
> align to the logical block size.
> 
> I tested this on a few raw block device types including nvme,
> virtio-blk, ahci, and loop. NVMe is the only one I tested with 4k
> logical sectors; everything else was 512.
> 
> On each of those, I tested several iomap filesystems: xfs, ext4, and
> btrfs. I found it interesting that each behave a little
> differently with handling invalid vector alignments:
> 
>    - XFS is the most straight forward and reports failures on invalid
>      vector conditions, same as raw blocks devices.
> 
>    - EXT4 falls back to buffered io for writes but not for reads.

I found it in ext4 too, i tried to fall the misaligned dio read request 
back to buffered io and submitted a patch[1], but haven't received any 
comments yet.

[1]:https://lore.kernel.org/all/20250710085910.123168-1-chensong_2000@189.cn/

Song
> 
>    - BTRFS doesn't even try direct io for any unusual alignments; it
>      chooses buffered io from the start.
> 
> So it has been a little slow going figuring out which results to expect
> from various tests, but I think I've got all the corner cases covered. I
> can submit the tests cases to blktests and fstests for consideration
> separately, too.
> 
> I'm not 100% sure where we're at with the last patch. I think Mike
> initially indicated this was okay to remove, but I could swear I read
> something saying that might not be the case anymore. I just can't find
> the message now. Mike?
> 
> Changes from v2:
> 
>    Include vector lengths when validating a split. The length check is
>    only valid for r/w commands, and skipped for passthrough
>    DRV_IN/DRV_OUT commands.
> 
>    Introduce a prep patch having bio_iov_iter_get_pages() take the
>    caller's desired length alignment.
> 
>    Additional code comments explaing less obvious error conditions.
> 
>    Added reviews on the patches that haven't changed.
> 
> Keith Busch (8):
>    block: check for valid bio while splitting
>    block: add size alignment to bio_iov_iter_get_pages
>    block: align the bio after building it
>    block: simplify direct io validity check
>    iomap: simplify direct io validity check
>    block: remove bdev_iter_is_aligned
>    blk-integrity: use simpler alignment check
>    iov_iter: remove iov_iter_is_aligned
> 
>   block/bio-integrity.c  |  4 +-
>   block/bio.c            | 64 ++++++++++++++++++----------
>   block/blk-map.c        |  2 +-
>   block/blk-merge.c      | 20 +++++++--
>   block/fops.c           | 13 +++---
>   fs/iomap/direct-io.c   |  6 +--
>   include/linux/bio.h    | 13 ++++--
>   include/linux/blkdev.h | 20 +++++----
>   include/linux/uio.h    |  2 -
>   lib/iov_iter.c         | 95 ------------------------------------------
>   10 files changed, 94 insertions(+), 145 deletions(-)
> 

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