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/
>
> > +
> > + 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 */
>
> The comment is a little confusing. Perhaps something like the following,
> if accurate..?
>
> /*
> * Disable perag reservations so it doesn't cause the allocation request
> * to fail. We'll reestablish reservation before we return.
> */
ok, will update in the next version.
>
> > + error = xfs_ag_resv_free(agibp->b_pag);
> > + if (error)
> > + return error;
> > +
> > + /* internal log shouldn't also show up in the free space btrees */
> > + error = xfs_alloc_vextent(&args);
> > + if (!error && args.agbno == NULLAGBLOCK)
> > + error = -ENOSPC;
> > +
> > + if (error) {
> > + /*
> > + * if extent allocation fails, need to roll the transaction to
> > + * ensure that the AGFL fixup has been committed anyway.
> > + */
> > + err2 = xfs_trans_roll(tpp);
> > + if (err2)
> > + return err2;
> > + goto resv_init_out;
>
> So if this fails and the transaction rolls, do we still hold the agi/agf
> buffers here? If not, there might be a window of time where it's
> possible for some other task to come in and alloc out of the AG without
> the perag res being active.
Yeah, I might need to bhold this, will update.
>
> > + }
> > +
> > + /*
> > + * if successfully deleted from freespace btrees, need to confirm
> > + * per-AG reservation works as expected.
> > + */
> > + be32_add_cpu(&agi->agi_length, -delta);
> > + be32_add_cpu(&agf->agf_length, -delta);
> > +
> > + err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> > + if (err2) {
> > + be32_add_cpu(&agi->agi_length, delta);
> > + be32_add_cpu(&agf->agf_length, delta);
> > + if (err2 != -ENOSPC)
> > + goto resv_err;
> > +
> > + __xfs_bmap_add_free(*tpp, args.fsbno, delta, NULL, true);
> > +
> > + /*
> > + * Roll the transaction before trying to re-init the per-ag
> > + * reservation. The new transaction is clean so it will cancel
> > + * without any side effects.
> > + */
> > + error = xfs_defer_finish(tpp);
> > + if (error)
> > + return error;
> > +
> > + error = -ENOSPC;
> > + goto resv_init_out;
> > + }
> > + xfs_ialloc_log_agi(*tpp, agibp, XFS_AGI_LENGTH);
> > + xfs_alloc_log_agf(*tpp, agfbp, XFS_AGF_LENGTH);
> > + return 0;
> > +
> > +resv_init_out:
> > + err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> > + if (!err2)
> > + return error;
> > +resv_err:
> > + xfs_warn(mp, "Error %d reserving per-AG metadata reserve pool.", err2);
> > + xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> > + return err2;
> > +}
> > +
> > /*
> > * Extent the AG indicated by the @id by the length passed in
> > */
> > 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/
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
> >
>
