Re: [PATCH 41/43] xfs: support write life time based data placement

Darrick J. Wong
2024-12-17T17:14:48Z

On Sun, Dec 15, 2024 at 07:19:02AM +0100, Christoph Hellwig wrote:
> On Fri, Dec 13, 2024 at 03:00:51PM -0800, Darrick J. Wong wrote:
> > > if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_FREE))
> > > oz = xfs_steal_open_zone_for_gc(zi);
> > > else
> > > - oz = xfs_open_zone(mp, true);
> > > + oz = xfs_open_zone(mp, WRITE_LIFE_NOT_SET, true);
> >
> > I wonder, is it possible to remember (at least incore) what write hint
> > was associated with an open zone all the way to gc time so that zones
> > with compatible hints can be gc'd into a new zone with the same hint?
> > Or is that overkill?
>
> We've been thinking about that a lot. Right now we don't have an
> immediate use case for it, but it sure would be nice to have it without
> needing another incompat bit. But then we'd need to find some space
> (3 bits to be exact) in the on-disk inode for it that doesn't make
> otherwise useful space unavaіlable for more widely useful things.
> If you have a good idea I'll look into implementing it.

How about reusing the dmapi fields in xfs_dinode, seeing as we forced
them to zero in the base metadir series? Or do you have another use in
mind for those 6 bytes?

--D