Re: [PATCH 07/11] vfs: add nowait parameter for file_accessed()

[Hao Xu]

On 8/29/23 19:53, Matthew Wilcox wrote:
> On Tue, Aug 29, 2023 at 03:46:13PM +0800, Hao Xu wrote:
> > On 8/28/23 05:32, Matthew Wilcox wrote:
> > > On Sun, Aug 27, 2023 at 09:28:31PM +0800, Hao Xu wrote:
> > > > From: Hao Xu <howeyxu@xxxxxxxxxxx>
> > > >
> > > > Add a boolean parameter for file_accessed() to support nowait semantics.
> > > > Currently it is true only with io_uring as its initial caller.
> > >
> > > So why do we need to do this as part of this series?  Apparently it
> > > hasn't caused any problems for filemap_read().
> >
> > We need this parameter to indicate if nowait semantics should be enforced in
> > touch_atime(), There are locks and maybe IOs in it.
>
> That's not my point.  We currently call file_accessed() and
> touch_atime() for nowait reads and nowait writes.  You haven't done
> anything to fix those.
>
> I suspect you can trim this patchset down significantly by avoiding
> fixing the file_accessed() problem.  And then come back with a later
> patchset that fixes it for all nowait i/o.  Or do a separate prep series

I'm ok to do that.

> first that fixes it for the existing nowait users, and then a second
> series to do all the directory stuff.
>
> I'd do the first thing.  Just ignore the problem.  Directory atime
> updates cause I/O so rarely that you can afford to ignore it.  Almost
> everyone uses relatime or nodiratime.

Hi Matthew,
The previous discussion shows this does cause issues in real
producations: 
https://lore.kernel.org/io-uring/2785f009-2ebb-028d-8250-d5f3a30510f0@xxxxxxxxx/#:~:text=fwiw%2C%20we%27ve%20just%20recently%20had%20similar%20problems%20with%20io_uring%20read/write