Re: Uneccesary flushes waking up suspended disks

[Dave Chinner <david@fromorbit.com>]

On Fri, Mar 15, 2024 at 10:05:16AM -0400, Phillip Susi wrote:
> Dave Chinner <david@fromorbit.com> writes:
> 
> > How do other filesystems behave? Is this a problem just on specific
> > filesystems?
> 
> I finally got around to testing other filesystems and surprisingly, it
> seems this is only a problem for ext4.

That's what I expected - I would have been surprised if you found
problems across multiple filesystems...

> I tried btrfs, f2fs, jfs, udf,
> and xfs.  xfs even uses the same jbd2 for journaling that ext4 does
> doesn't it?

.... because none of them share "journalling" code at all. They all
have their own independent mechanisms for ensuring data and metadata
integrity. ext4/jbd2 actually shares little code with other Linux
filesystems - ocfs2 is the only other linux filesystem that uses
jbd2.

> I just formatted a clean fs, synced, and ran blktrace, then synced
> again, and only ext4 emits a flush on the second sync.

So this really sounds like it's just a bug in ext4/jbd2 behaviour
and so there's no real general filesystem or infrastructure
problem that needs to be fixed here....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com