netdev - Re: [PATCH 07/11] vfs: add nowait parameter for file

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Date: Tue, 29 Aug 2023 12:53:07 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Hao Xu <hao.xu@...ux.dev>
Cc: io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Pavel Begunkov <asml.silence@...il.com>,
	Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
	Dave Chinner <david@...morbit.com>,
	"Darrick J . Wong" <djwong@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-cachefs@...hat.com,
	ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-unionfs@...r.kernel.org, bpf@...r.kernel.org,
	netdev@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-btrfs@...r.kernel.org, codalist@...a.cs.cmu.edu,
	linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
	linux-mm@...ck.org, linux-nilfs@...r.kernel.org,
	devel@...ts.orangefs.org, linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org, linux-mtd@...ts.infradead.org,
	Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 07/11] vfs: add nowait parameter for file_accessed()

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@...cent.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
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.