linux-ext4 - Re: [RFC[RAP] V2] fuse: use fs-iomap for better performance so we can containerize ext4

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Message-ID: <20250701060526.GH9987@frogsfrogsfrogs>
Date: Mon, 30 Jun 2025 23:05:26 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Amir Goldstein <amir73il@...il.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>, John@...ves.net,
	bernd@...ernd.com, joannelkoong@...il.com,
	Josef Bacik <josef@...icpanda.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>, Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC[RAP] V2] fuse: use fs-iomap for better performance so we
 can containerize ext4

On Mon, Jun 23, 2025 at 03:16:53PM +0200, Miklos Szeredi wrote:
> On Fri, 13 Jun 2025 at 19:37, Darrick J. Wong <djwong@...nel.org> wrote:
> 
> > Top of that list is timestamps and file attributes, because fuse no
> > longer calls the fuse server for file writes.  As a result, the kernel
> > inode always has the most uptodate versions of the some file attributes
> > (i_size, timestamps, mode) and just want to send FUSE_SETATTR whenever
> > the dirty inode gets flushed.
> 
> This is already the case for cached writes, no new code should be needed.

Are you talking about the fc->writeback_cache stuff?  Yeah, that mostly
works out for fuse2fs.  Though I was wondering, when does atime get
updated?  fs/fuse sets S_NOATIME, so I guess it's up to the fuse server
to update it when it wants to, and a later FUSE_GETATTR can pick it up?
If so, how do fuse servers implement lazytime/relatime?

--D

> Thanks,
> Miklos
>