On Mon, Mar 22, 2021 at 08:03:10PM +0800, Gao Xiang wrote:
> Hi Brian,
>
> On Mon, Mar 22, 2021 at 07:30:03AM -0400, Brian Foster wrote:
> > On Fri, Mar 05, 2021 at 10:57:01AM +0800, Gao Xiang wrote:
> > > This patch introduces a helper to shrink unused space in the last AG
> > > by fixing up the freespace btree.
> > >
> > > Also make sure that the per-AG reservation works under the new AG
> > > size. If such per-AG reservation or extent allocation fails, roll
> > > the transaction so the new transaction could cancel without any side
> > > effects.
> > >
> > > Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
> > > ---
> >
> > Looks mostly good to me. Some nits..
> >
> > > fs/xfs/libxfs/xfs_ag.c | 111 +++++++++++++++++++++++++++++++++++++++++
> > > fs/xfs/libxfs/xfs_ag.h | 4 +-
> > > 2 files changed, 114 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > > index 9331f3516afa..1f6f9e70e1cb 100644
> > > --- a/fs/xfs/libxfs/xfs_ag.c
> > > +++ b/fs/xfs/libxfs/xfs_ag.c
> > ...
> > > @@ -485,6 +490,112 @@ xfs_ag_init_headers(
> > > return error;
> > > }
> > >
> > > +int
> > > +xfs_ag_shrink_space(
> > > + struct xfs_mount *mp,
> > > + struct xfs_trans **tpp,
> > > + xfs_agnumber_t agno,
> > > + xfs_extlen_t delta)
> > > +{
> > > + struct xfs_alloc_arg args = {
> > > + .tp = *tpp,
> > > + .mp = mp,
> > > + .type = XFS_ALLOCTYPE_THIS_BNO,
> > > + .minlen = delta,
> > > + .maxlen = delta,
> > > + .oinfo = XFS_RMAP_OINFO_SKIP_UPDATE,
> > > + .resv = XFS_AG_RESV_NONE,
> > > + .prod = 1
> > > + };
> > > + struct xfs_buf *agibp, *agfbp;
> > > + struct xfs_agi *agi;
> > > + struct xfs_agf *agf;
> > > + int error, err2;
> > > +
> > > + ASSERT(agno == mp->m_sb.sb_agcount - 1);
> > > + error = xfs_ialloc_read_agi(mp, *tpp, agno, &agibp);
> > > + if (error)
> > > + return error;
> > > +
> > > + agi = agibp->b_addr;
> > > +
> > > + error = xfs_alloc_read_agf(mp, *tpp, agno, 0, &agfbp);
> > > + if (error)
> > > + return error;
> > > +
> > > + agf = agfbp->b_addr;
> > > + if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > > + return -EFSCORRUPTED;
> >
> > Is this check here for a reason? It seems a bit random, so I wonder if
> > we should just leave the extra verification to buffer verifiers.
>
> It came from Darrick's thought. I'm fine with either way, but I feel
> confused if different conflict opinions here:
> https://lore.kernel.org/linux-xfs/20210303181931.GB3419940@magnolia/
>
Darrick's comment seems to refer to the check below. I'm referring to
the check above that agi_length and agf_length match. Are they intended
to go together? The check above seems to preexist the one below.
Anyways, if so, maybe just bunch them together and add a comment:
/* some extra paranoid checks before we shrink the ag */
if (XFS_IS_CORRUPT(...))
return -EFSCORRUPTED;
if (delta >= agf->agf_length)
return -EVINAL;
> >
> > > +
> > > + if (delta >= agi->agi_length)
> > > + return -EINVAL;
> > > +
> > > + args.fsbno = XFS_AGB_TO_FSB(mp, agno,
> > > + be32_to_cpu(agi->agi_length) - delta);
> > > +
> > > + /* remove the preallocations before allocation and re-establish then */
...
> > > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> > > index 5166322807e7..41293ebde8da 100644
> > > --- a/fs/xfs/libxfs/xfs_ag.h
> > > +++ b/fs/xfs/libxfs/xfs_ag.h
> > > @@ -24,8 +24,10 @@ struct aghdr_init_data {
> > > };
> > >
> > > int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
> > > +int xfs_ag_shrink_space(struct xfs_mount *mp, struct xfs_trans **tpp,
> > > + xfs_agnumber_t agno, xfs_extlen_t len);
> > > int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
> > > - struct aghdr_init_data *id, xfs_extlen_t len);
> > > + struct aghdr_init_data *id, xfs_extlen_t delta);
> >
> > This looks misplaced..?
> >
> > Or maybe this is trying to make the APIs consistent, but the function
> > definition still uses len as well as the declaration for
> > _ag_shrink_space() (while the definition of that function uses delta).
> >
> > FWIW, the name delta tends to suggest a signed value to me based on our
> > pattern of usage, whereas here it seems like these helpers always want a
> > positive value (i.e. a length).
>
> Yeah, it's just misplaced, thanks for pointing out, sorry about that.
> `delta' name came from, `len' is confusing to Darrick.
> https://lore.kernel.org/r/20210303182527.GC3419940@magnolia/
>
Fair enough. I'm not worried about the name, just pointing out some
potential inconsistencies.
Brian
> Thanks,
> Gao Xiang
>
> >
> > Brian
> >
> > > int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,
> > > struct xfs_ag_geometry *ageo);
> > >
> > > --
> > > 2.27.0
> > >
> >
>
