On Mon, Mar 22, 2021 at 08:43:19AM -0400, Brian Foster wrote:
> On Mon, Mar 22, 2021 at 08:36:52PM +0800, Gao Xiang wrote:
> > On Mon, Mar 22, 2021 at 08:26:41AM -0400, Brian Foster wrote:
> > > On Mon, Mar 22, 2021 at 08:07:22PM +0800, Gao Xiang wrote:
> > > > On Mon, Mar 22, 2021 at 07:30:40AM -0400, Brian Foster wrote:
> > > > > On Fri, Mar 05, 2021 at 10:57:02AM +0800, Gao Xiang wrote:
> > > > > > As the first step of shrinking, this attempts to enable shrinking
> > > > > > unused space in the last allocation group by fixing up freespace
> > > > > > btree, agi, agf and adjusting super block and use a helper
> > > > > > xfs_ag_shrink_space() to fixup the last AG.
> > > > > >
> > > > > > This can be all done in one transaction for now, so I think no
> > > > > > additional protection is needed.
> > > > > >
> > > > > > Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> > > > > > Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
> > > > > > ---
> > > > > > fs/xfs/xfs_fsops.c | 88 ++++++++++++++++++++++++++++------------------
> > > > > > fs/xfs/xfs_trans.c | 1 -
> > > > > > 2 files changed, 53 insertions(+), 36 deletions(-)
> > > > > >
> > > > > > diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> > > > > > index fc9e799b2ae3..71cba61a451c 100644
> > > > > > --- a/fs/xfs/xfs_fsops.c
> > > > > > +++ b/fs/xfs/xfs_fsops.c
> > > ...
> > > > > > @@ -115,10 +120,15 @@ xfs_growfs_data_private(
> > > > > > if (nb_mod && nb_mod < XFS_MIN_AG_BLOCKS) {
> > > > > > nagcount--;
> > > > > > nb = (xfs_rfsblock_t)nagcount * mp->m_sb.sb_agblocks;
> > > > > > - if (nb < mp->m_sb.sb_dblocks)
> > > > > > - return -EINVAL;
> > > > > > }
> > > > > > delta = nb - mp->m_sb.sb_dblocks;
> > > > > > + /*
> > > > > > + * XFS doesn't really support single-AG filesystems, so do not
> > > > > > + * permit callers to remove the filesystem's second and last AG.
> > > > > > + */
> > > > > > + if (delta < 0 && nagcount < 2)
> > > > > > + return -EINVAL;
> > > > > > +
> > > > >
> > > > > What if the filesystem is already single AG? Unless I'm missing
> > > > > something, we already have a check a bit further down that prevents
> > > > > removal of AGs in the first place.
> > > >
> > > > I think it tends to forbid (return -EINVAL) shrinking the filesystem with
> > > > a single AG only? Am I missing something?
> > > >
> > >
> > > My assumption was this check means one can't shrink a filesystem that is
> > > already agcount == 1. The comment refers to preventing shrink from
> > > causing an agcount == 1 fs. What is the intent?
> >
> > I think it means the latter -- preventing shrink from causing an agcount == 1
> > fs. since nagcount (new agcount) <= 1?
> >
>
> Right, so that leads to my question... does this check also fail a
> shrink on an fs that is already agcount == 1? If so, why? I know
> technically it's not a supported configuration, but mkfs allows it.
Ah, I'm not sure if Darrick would like to forbid agcount == 1 shrinking
functionitity completely, see the previous comment:
https://lore.kernel.org/r/20201014160633.GD9832@magnolia/
(please ignore the modification at that time, since it was buggy...)
Thanks,
Gao Xiang
>
> Brian
>
> > Actually, I'm not good at English, if comments need to be improved, please
> > kindly point out. Thank you very much!
> >
> > Thanks,
> > Gao Xiang
> >
> > >
> > > Brian
> > >
> > > > Thanks,
> > > > Gao Xiang
> > > >
> > > > >
> > > > > Otherwise looks reasonable..
> > > > >
> > > > > Brian
> > > > >
> > > > > > oagcount = mp->m_sb.sb_agcount;
> > > > > >
> > > > > > /* allocate the new per-ag structures */
> > > > > > @@ -126,15 +136,22 @@ xfs_growfs_data_private(
> > > > > > error = xfs_initialize_perag(mp, nagcount, &nagimax);
> > > > > > if (error)
> > > > > > return error;
> > > > > > + } else if (nagcount < oagcount) {
> > > > > > + /* TODO: shrinking the entire AGs hasn't yet completed */
> > > > > > + return -EINVAL;
> > > > > > }
> > > > > >
> > > > > > error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata,
> > > > > > - XFS_GROWFS_SPACE_RES(mp), 0, XFS_TRANS_RESERVE, &tp);
> > > > > > + (delta > 0 ? XFS_GROWFS_SPACE_RES(mp) : -delta), 0,
> > > > > > + XFS_TRANS_RESERVE, &tp);
> > > > > > if (error)
> > > > > > return error;
> > > > > >
> > > > > > - error = xfs_resizefs_init_new_ags(tp, &id, oagcount, nagcount,
> > > > > > - delta, &lastag_resetagres);
> > > > > > + if (delta > 0)
> > > > > > + error = xfs_resizefs_init_new_ags(tp, &id, oagcount, nagcount,
> > > > > > + delta, &lastag_resetagres);
> > > > > > + else
> > > > > > + error = xfs_ag_shrink_space(mp, &tp, nagcount - 1, -delta);
> > > > > > if (error)
> > > > > > goto out_trans_cancel;
> > > > > >
> > > > > > @@ -145,7 +162,7 @@ xfs_growfs_data_private(
> > > > > > */
> > > > > > if (nagcount > oagcount)
> > > > > > xfs_trans_mod_sb(tp, XFS_TRANS_SB_AGCOUNT, nagcount - oagcount);
> > > > > > - if (delta > 0)
> > > > > > + if (delta)
> > > > > > xfs_trans_mod_sb(tp, XFS_TRANS_SB_DBLOCKS, delta);
> > > > > > if (id.nfree)
> > > > > > xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, id.nfree);
> > > > > > @@ -169,28 +186,29 @@ xfs_growfs_data_private(
> > > > > > xfs_set_low_space_thresholds(mp);
> > > > > > mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);
> > > > > >
> > > > > > - /*
> > > > > > - * If we expanded the last AG, free the per-AG reservation
> > > > > > - * so we can reinitialize it with the new size.
> > > > > > - */
> > > > > > - if (lastag_resetagres) {
> > > > > > - struct xfs_perag *pag;
> > > > > > -
> > > > > > - pag = xfs_perag_get(mp, id.agno);
> > > > > > - error = xfs_ag_resv_free(pag);
> > > > > > - xfs_perag_put(pag);
> > > > > > - if (error)
> > > > > > - return error;
> > > > > > + if (delta > 0) {
> > > > > > + /*
> > > > > > + * If we expanded the last AG, free the per-AG reservation
> > > > > > + * so we can reinitialize it with the new size.
> > > > > > + */
> > > > > > + if (lastag_resetagres) {
> > > > > > + struct xfs_perag *pag;
> > > > > > +
> > > > > > + pag = xfs_perag_get(mp, id.agno);
> > > > > > + error = xfs_ag_resv_free(pag);
> > > > > > + xfs_perag_put(pag);
> > > > > > + if (error)
> > > > > > + return error;
> > > > > > + }
> > > > > > + /*
> > > > > > + * Reserve AG metadata blocks. ENOSPC here does not mean there
> > > > > > + * was a growfs failure, just that there still isn't space for
> > > > > > + * new user data after the grow has been run.
> > > > > > + */
> > > > > > + error = xfs_fs_reserve_ag_blocks(mp);
> > > > > > + if (error == -ENOSPC)
> > > > > > + error = 0;
> > > > > > }
> > > > > > -
> > > > > > - /*
> > > > > > - * Reserve AG metadata blocks. ENOSPC here does not mean there was a
> > > > > > - * growfs failure, just that there still isn't space for new user data
> > > > > > - * after the grow has been run.
> > > > > > - */
> > > > > > - error = xfs_fs_reserve_ag_blocks(mp);
> > > > > > - if (error == -ENOSPC)
> > > > > > - error = 0;
> > > > > > return error;
> > > > > >
> > > > > > out_trans_cancel:
> > > > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > > > > > index 44f72c09c203..d047f5f26cc0 100644
> > > > > > --- a/fs/xfs/xfs_trans.c
> > > > > > +++ b/fs/xfs/xfs_trans.c
> > > > > > @@ -434,7 +434,6 @@ xfs_trans_mod_sb(
> > > > > > tp->t_res_frextents_delta += delta;
> > > > > > break;
> > > > > > case XFS_TRANS_SB_DBLOCKS:
> > > > > > - ASSERT(delta > 0);
> > > > > > tp->t_dblocks_delta += delta;
> > > > > > break;
> > > > > > case XFS_TRANS_SB_AGCOUNT:
> > > > > > --
> > > > > > 2.27.0
> > > > > >
> > > > >
> > > >
> > >
> >
>
