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From: "Darrick J. Wong" <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Al Viro <[email protected]>, Stefan Roesch <[email protected]>,
	[email protected], [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected], [email protected],
	Christoph Hellwig <[email protected]>
Subject: Re: [PATCH v7 15/15] xfs: Add async buffered write support
Date: Fri, 1 Jul 2022 11:05:28 -0700	[thread overview]
Message-ID: <Yr83aD0yuEwvJ7tL@magnolia> (raw)
In-Reply-To: <[email protected]>

On Fri, Jul 01, 2022 at 08:38:07AM -0600, Jens Axboe wrote:
> On 7/1/22 8:30 AM, Jens Axboe wrote:
> > On 7/1/22 8:19 AM, Jens Axboe wrote:
> >> On 6/30/22 10:39 PM, Al Viro wrote:
> >>> On Wed, Jun 01, 2022 at 02:01:41PM -0700, Stefan Roesch wrote:
> >>>> This adds the async buffered write support to XFS. For async buffered
> >>>> write requests, the request will return -EAGAIN if the ilock cannot be
> >>>> obtained immediately.
> >>>
> >>> breaks generic/471...
> >>
> >> That test case is odd, because it makes some weird assumptions about
> >> what RWF_NOWAIT means. Most notably that it makes it mean if we should
> >> instantiate blocks or not. Where did those assumed semantics come from?
> >> On the read side, we have clearly documented that it should "not wait
> >> for data which is not immediately available".
> >>
> >> Now it is possible that we're returning a spurious -EAGAIN here when we
> >> should not be. And that would be a bug imho. I'll dig in and see what's
> >> going on.
> > 
> > This is the timestamp update that needs doing which will now return
> > -EAGAIN if IOCB_NOWAIT is set as it may block.
> > 
> > I do wonder if we should just allow inode time updates with IOCB_NOWAIT,
> > even on the io_uring side. Either that, or passed in RWF_NOWAIT
> > semantics don't map completely to internal IOCB_NOWAIT semantics. At
> > least in terms of what generic/471 is doing, but I'm not sure who came
> > up with that and if it's established semantics or just some made up ones
> > from whomever wrote that test. I don't think they make any sense, to be
> > honest.
> 
> Further support that generic/471 is just randomly made up semantics,
> it needs to special case btrfs with nocow or you'd get -EAGAIN anyway
> for that test.
> 
> And it's relying on some random timing to see if this works. I really
> think that test case is just hot garbage, and doesn't test anything
> meaningful.

<shrug> I had thought that NOWAIT means "don't wait for *any*thing",
which would include timestamp updates... but then I've never been all
that clear on what specifically NOWAIT will and won't wait for. :/

--D

> -- 
> Jens Axboe
> 

  reply	other threads:[~2022-07-01 18:05 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-01 21:01 [PATCH v7 00/15] io-uring/xfs: support async buffered writes Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 01/15] mm: Move starting of background writeback into the main balancing loop Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 02/15] mm: Move updates of dirty_exceeded into one place Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 03/15] mm: Add balance_dirty_pages_ratelimited_flags() function Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 04/15] iomap: Add flags parameter to iomap_page_create() Stefan Roesch
2022-06-02 16:26   ` Darrick J. Wong
2022-06-01 21:01 ` [PATCH v7 05/15] iomap: Add async buffered write support Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 06/15] iomap: Return error code from iomap_write_iter() Stefan Roesch
2022-06-02 12:38   ` Matthew Wilcox
2022-06-02 17:08     ` Stefan Roesch
2022-06-06 16:39     ` Stefan Roesch
2022-06-06 19:18       ` Matthew Wilcox
2022-06-06 19:21         ` Stefan Roesch
2022-06-06 19:25           ` Matthew Wilcox
2022-06-06 19:28             ` Stefan Roesch
2022-06-06 20:30               ` Matthew Wilcox
2022-06-06 20:34                 ` Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 07/15] fs: Add check for async buffered writes to generic_write_checks Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 08/15] fs: add __remove_file_privs() with flags parameter Stefan Roesch
2022-06-02  9:04   ` Jan Kara
2022-06-01 21:01 ` [PATCH v7 09/15] fs: Split off inode_needs_update_time and __file_update_time Stefan Roesch
2022-06-02  8:44   ` Jan Kara
2022-06-02 12:57   ` Matthew Wilcox
2022-06-02 21:04     ` Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 10/15] fs: Add async write file modification handling Stefan Roesch
2022-06-02  8:44   ` Jan Kara
2022-06-02  9:06   ` Jan Kara
2022-06-02 21:00     ` Stefan Roesch
2022-06-03 10:12       ` Jan Kara
2022-06-06 16:35         ` Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 11/15] fs: Optimization for concurrent file time updates Stefan Roesch
2022-06-02  8:59   ` Jan Kara
2022-06-02 21:06     ` Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 12/15] io_uring: Add support for async buffered writes Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 13/15] io_uring: Add tracepoint for short writes Stefan Roesch
2022-06-01 21:01 ` [PATCH v7 14/15] xfs: Specify lockmode when calling xfs_ilock_for_iomap() Stefan Roesch
2022-06-02 16:25   ` Darrick J. Wong
2022-06-01 21:01 ` [PATCH v7 15/15] xfs: Add async buffered write support Stefan Roesch
2022-07-01  4:39   ` Al Viro
2022-07-01 14:19     ` Jens Axboe
2022-07-01 14:30       ` Jens Axboe
2022-07-01 14:38         ` Jens Axboe
2022-07-01 18:05           ` Darrick J. Wong [this message]
2022-07-01 18:14             ` Jens Axboe
2022-07-05 13:47               ` Josef Bacik
2022-07-05 14:23                 ` Goldwyn Rodrigues
2022-07-05 16:11                 ` Christoph Hellwig
2022-06-02  8:09 ` [PATCH v7 00/15] io-uring/xfs: support async buffered writes Jens Axboe
2022-06-03  2:43   ` Dave Chinner
2022-06-03 13:04     ` Jens Axboe
2022-06-07 16:41       ` Stefan Roesch

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