Re: [PATCH 9/9] spaceman/defrag: warn on extsize

[Dave Chinner <david@fromorbit.com>]

On Thu, Jul 11, 2024 at 11:36:28PM +0000, Wengang Wang wrote:
> 
> 
> > On Jul 9, 2024, at 1:21 PM, Darrick J. Wong <djwong@kernel.org> wrote:
> > 
> > On Tue, Jul 09, 2024 at 12:10:28PM -0700, Wengang Wang wrote:
> >> According to current kernel implemenation, non-zero extsize might affect
> >> the result of defragmentation.
> >> Just print a warning on that if non-zero extsize is set on file.
> > 
> > I'm not sure what's the point of warning vaguely about extent size
> > hints?  I'd have thought that would help reduce the number of extents;
> > is that not the case?
> 
> Not exactly.
> 
> Same 1G file with about 54K extents,
> 
> The one with 16K extsize, after defrag, it’s extents drops to 13K.
> And the one with 0 extsize, after defrag, it’s extents dropped to 22.

extsize should not affect file contiguity like this at all. Are you
measuring fragmentation correctly? i.e. a contiguous region from an
larger extsize allocation that results in a bmap/fiemap output of
three extents in a unwritten/written/unwritten is not fragmentation.

-Dave.
-- 
Dave Chinner
david@fromorbit.com