Hi Darrick,
On Wed, Jan 20, 2021 at 11:25:06AM -0800, Darrick J. Wong wrote:
> On Mon, Jan 18, 2021 at 04:36:59PM +0800, Gao Xiang wrote:
...
> >
> > +int
> > +xfs_ag_shrink_space(
> > + struct xfs_mount *mp,
> > + struct xfs_trans *tp,
> > + struct aghdr_init_data *id,
> > + xfs_extlen_t len)
> > +{
> > + struct xfs_alloc_arg args = {
> > + .tp = tp,
> > + .mp = mp,
> > + .type = XFS_ALLOCTYPE_THIS_BNO,
> > + .minlen = len,
> > + .maxlen = len,
> > + .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(id->agno == mp->m_sb.sb_agcount - 1);
> > + error = xfs_ialloc_read_agi(mp, tp, id->agno, &agibp);
> > + if (error)
> > + return error;
> > +
> > + agi = agibp->b_addr;
> > +
> > + error = xfs_alloc_read_agf(mp, tp, id->agno, 0, &agfbp);
> > + if (error)
> > + return error;
> > +
> > + agf = agfbp->b_addr;
> > + if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
> > + return -EFSCORRUPTED;
> > +
> > + args.fsbno = XFS_AGB_TO_FSB(mp, id->agno,
> > + be32_to_cpu(agi->agi_length) - len);
> > +
> > + /* remove the preallocations before allocation and re-establish then */
> > + 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) {
>
> Aha, now I see why this bit:
>
> if (!extend && ((tp->t_flags & XFS_TRANS_DIRTY) ||
> !list_empty(&tp->t_dfops)))
> xfs_trans_commit(tp);
>
> is needed below -- we could have refilled the AGFL here but failed the
> allocation. At this point we have a dirty transaction /and/ an error
> code. We need to commit the AGFL refill changes and return to userspace
> with that error code, but calling xfs_trans_cancel on the dirty
> transaction causes an (unnecessary) shutdown.
>
> What if you rolled the transaction here and passed the new tp and the
> error code back to the caller? The new transaction is clean so it will
> cancel without any side effects, and then you can send the ENOSPC up to
> userspace.
>
> Granted, you could just as easily commit the transaction here and make
> the caller smart enough to know that it no longer has a transaction. I
> wonder if the transaction allocation and disposal ought to be part of
> the _ag_grow_space and _ag_shrink_space functions.
>
> Also fwiw I would make sure the transaction is clean before I tried to
> re-initialize the per-ag reservation.
Thanks for your review!
Okay, will look into roll transaction way instead (at least for
the new _ag_shrink_space() since I don't touch _grow_space and
not sure if it has AGFL refill issue as well...)
>
> > + err2 = xfs_ag_resv_init(agibp->b_pag, tp);
> > + if (err2)
> > + goto resv_err;
> > + return error;
> > + }
> > +
> > + /*
> > + * if successfully deleted from freespace btrees, need to confirm
> > + * per-AG reservation works as expected.
> > + */
> > + be32_add_cpu(&agi->agi_length, -len);
> > + be32_add_cpu(&agf->agf_length, -len);
> > +
> > + err2 = xfs_ag_resv_init(agibp->b_pag, tp);
> > + if (err2) {
> > + be32_add_cpu(&agi->agi_length, len);
> > + be32_add_cpu(&agf->agf_length, len);
> > + if (err2 != -ENOSPC)
> > + goto resv_err;
>
> If we've just undone reducing ag[if]_length, don't we need to call
> xfs_ag_resv_init here to (try to) recreate the former per-ag
> reservations?
If my understanding is correct, xfs_fs_reserve_ag_blocks() in
xfs_growfs_data_private() would do that for all AGs... Do we
need to xfs_ag_resv_init() in advance here?
I thought xfs_ag_resv_init() here is mainly used to guarantee the
per-AG reservation for resized size is fine... if ag{i,f}_length
don't change, leave such normal reservation to
xfs_fs_reserve_ag_blocks() would be okay?
>
> Also, the comment above about cleaning the transaction before trying to
> reinit the per-ag reservation and returning ENOSPC applies here.
ok. that'd be here if rolling a new transaction is needed.
Thanks for the reminder!
Thanks,
Gao Xiang
>
> > +
> > + __xfs_bmap_add_free(tp, args.fsbno, len,
> > + &XFS_RMAP_OINFO_SKIP_UPDATE, true);
> > + return err2;
> > + }
> > + xfs_ialloc_log_agi(tp, agibp, XFS_AGI_LENGTH);
> > + xfs_alloc_log_agf(tp, agfbp, XFS_AGF_LENGTH);
> > + return 0;
> > +
> > +resv_err:
> > + xfs_warn(mp,
> > +"Error %d reserving per-AG metadata reserve pool.", err2);
> > + xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> > + return err2;
> > +}
