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From: Jens Axboe <[email protected]>
To: Christoph Hellwig <[email protected]>,
	Matthew Wilcox <[email protected]>
Cc: Stefan Roesch <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [PATCH v2 04/13] fs: split off __alloc_page_buffers function
Date: Tue, 22 Feb 2022 16:19:41 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 2/22/22 1:18 AM, Christoph Hellwig wrote:
> On Sun, Feb 20, 2022 at 04:23:50AM +0000, Matthew Wilcox wrote:
>> On Fri, Feb 18, 2022 at 11:35:10PM -0800, Christoph Hellwig wrote:
>>> Err, hell no.  Please do not add any new functionality to the legacy
>>> buffer head code.  If you want new features do that on the
>>> non-bufferhead iomap code path only please.
>>
>> I think "first convert the block device code from buffer_heads to iomap"
>> might be a bit much of a prerequisite.  I think running ext4 on top of a
>> block device still requires buffer_heads, for example (I tried to convert
>> the block device to use mpage in order to avoid creating buffer_heads
>> when possible, and ext4 stopped working.  I didn't try too hard to debug
>> it as it was a bit of a distraction at the time).
> 
> Oh, I did not spot the users here is the block device.  Which is
> really weird, why would anyone do buffered writes to a block devices?
> Doing so is a bit of a data integrity nightmare.
> 
> Can we please develop this feature for iomap based file systems first,
> and if by then a use case for block devices arises I'll see what we
> can do there.

The original plan wasn't to develop bdev async writes as a separate
useful feature, but rather to do it as a first step to both become
acquainted with the code base and solve some of the common issues for
both.

The fact that we need to touch buffer_heads for the bdev path is
annoying, and something that I'd very much rather just avoid. And
converting bdev to iomap first is a waste of time, exactly because it's
not a separately useful feature.

Hence I think we'll change gears here and start with iomap and XFS
instead.

> I've been planning to get the block device code to stop using
> buffer_heads by default, but taking them into account if used by a
> legacy buffer_head user anyway.

That would indeed be great, and to be honest, the current code for bdev
read/write doesn't make much sense outside of from a historical point of
view.

-- 
Jens Axboe


  reply	other threads:[~2022-02-22 23:19 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-18 19:57 [PATCH v2 00/13] Support sync buffered writes for io-uring Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 01/13] fs: Add flags parameter to __block_write_begin_int Stefan Roesch
2022-02-18 19:59   ` Matthew Wilcox
2022-02-18 20:08     ` Stefan Roesch
2022-02-18 20:13       ` Matthew Wilcox
2022-02-18 20:14         ` Stefan Roesch
2022-02-18 20:22           ` Matthew Wilcox
2022-02-18 20:25             ` Stefan Roesch
2022-02-18 20:35               ` Matthew Wilcox
2022-02-18 20:39                 ` Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 02/13] mm: Introduce do_generic_perform_write Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 03/13] mm: Add support for async buffered writes Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 04/13] fs: split off __alloc_page_buffers function Stefan Roesch
2022-02-18 20:42   ` Matthew Wilcox
2022-02-18 20:50     ` Stefan Roesch
2022-02-19  7:35   ` Christoph Hellwig
2022-02-20  4:23     ` Matthew Wilcox
2022-02-20  4:38       ` Jens Axboe
2022-02-20  4:51         ` Jens Axboe
2022-02-22  8:18       ` Christoph Hellwig
2022-02-22 23:19         ` Jens Axboe [this message]
2022-02-18 19:57 ` [PATCH v2 05/13] fs: split off __create_empty_buffers function Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 06/13] fs: Add gfp_t parameter to create_page_buffers() Stefan Roesch
2022-02-21  0:18   ` kernel test robot
2022-02-18 19:57 ` [PATCH v2 07/13] fs: add support for async buffered writes Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 08/13] io_uring: " Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 09/13] io_uring: Add tracepoint for short writes Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 10/13] sched: add new fields to task_struct Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 11/13] mm: support write throttling for async buffered writes Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 12/13] io_uring: " Stefan Roesch
2022-02-18 19:57 ` [PATCH v2 13/13] block: enable async buffered writes for block devices Stefan Roesch
2022-02-20 22:38 ` [PATCH v2 00/13] Support sync buffered writes for io-uring Dave Chinner

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