Re: [PATCH v2 1/3] quota: add quota in-memory format support

[Jan Kara <jack@suse.cz>]

On Fri 25-11-22 10:30:10, Lukas Czerner wrote:
> On Wed, Nov 23, 2022 at 06:07:39PM +0100, Jan Kara wrote:
> > On Mon 21-11-22 15:28:52, Lukas Czerner wrote:
> > Instead of this I'd define:
> > 
> > struct shmem_dquot {
> >         struct rb_node node;
> >         qid_t id;
> > 	qsize_t bhardlimit;
> > 	qsize_t bsoftlimit;
> > 	qsize_t ihardlimit;
> > 	qsize_t isoftlimit;
> > };
> > 
> > It would be kept in rbtree like you do with quota_id but it will be also
> > used as ultimate "persistent" storage of quota information when dquot gets
> > reclaimed. We don't need to store grace times or usage information because
> > if there is non-zero usage, dquot is referenced from the inode and thus
> > cannot be reclaimed.
> 
> Ok, this approach will duplicate the limits, but has advantage of having
> much smaller footprint than entire dquot so in case we don't have any
> usage in dquot we can safely reclaim it if needed without loosing user
> provided limits. Probably a worthwhile trade-off.
> 
> Or perhaps we can eliminate the duplicity when we store it in the tree on
> ->destroy_dquot() and free it after we load the limits into dquot on
> ->acquire_dquo().

We could but I don't think it's worth the hassle. In particular because
->release_dquot() must not fail (there's no simple way to recover from such
failure). I don't say it is impossible to overcome but just not worth the
saved memory IMHO.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR