linux-ext4 - Re: [PATCHBOMB v6] fuse: containerize ext4 for safer operation

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Message-ID: <20251031175620.GQ6174@frogsfrogsfrogs>
Date: Fri, 31 Oct 2025 10:56:20 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Joanne Koong <joannelkoong@...il.com>
Cc: linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Bernd Schubert <bernd@...ernd.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>, Neal Gompa <neal@...pa.dev>,
	Amir Goldstein <amir73il@...il.com>,
	Christian Brauner <brauner@...nel.org>,
	Jeff Layton <jlayton@...nel.org>
Subject: Re: [PATCHBOMB v6] fuse: containerize ext4 for safer operation

On Thu, Oct 30, 2025 at 09:35:25AM -0700, Joanne Koong wrote:
> On Tue, Oct 28, 2025 at 5:27 PM Darrick J. Wong <djwong@...nel.org> wrote:
> >
> > At this stage I still get about 95% of the kernel ext4 driver's
> > streaming directio performance on streaming IO, and 110% of its
> > streaming buffered IO performance.  Random buffered IO is about 85% as
> 
> Do you know why this is faster than ext4 sequential buffered IO?

The last time I looked, ext4 still uses buffer heads and 4k folios, even
for regular files that don't have any fancy features.  IOWs, the iomap
port for kernel ext4 remains unmerged.

--D

> Thanks,
> Joanne
> 
> > fast as the kernel.  Random direct IO is about 80% as fast as the
> > kernel; see the cover letter for the fuse2fs iomap changes for more
> > details.  Unwritten extent conversions on random direct writes are
> > especially painful for fuse+iomap (~90% more overhead) due to upcall
> > overhead.  And that's with (now dynamic) debugging turned on!
> >
>