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

Hao Xu
2023-08-30T06:18:30Z

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@tencent.com>
>>>>
>>>> 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@gmail.com/#:~:text=fwiw%2C%20we%27ve%20just%20recently%20had%20similar%20problems%20with%20io_uring%20read/write