Re: [PATCH 2/3] writeback: allow the file system to override MIN_WRITEBACK_PAGES

Dave Chinner
2025-10-15T20:49:27Z

On Wed, Oct 15, 2025 at 03:27:15PM +0900, Christoph Hellwig wrote:
> The relatively low minimal writeback size of 4MiB leads means that
> written back inodes on rotational media are switched a lot. Besides
> introducing additional seeks, this also can lead to extreme file
> fragmentation on zoned devices when a lot of files are cached relative
> to the available writeback bandwidth.
>
> Add a superblock field that allows the file system to override the
> default size.

Hmmm - won't changing this for the zoned rtdev also change behaviour
for writeback on the data device? i.e. upping the minimum for the
normal data device on XFS will mean writeback bandwidth sharing is a
lot less "fair" and higher latency when we have a mix of different
file sizes than it currently is...

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