On Tue, Jan 26, 2021 at 08:56:20PM +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.
>
> Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
> ---
> fs/xfs/xfs_fsops.c | 64 ++++++++++++++++++++++++++++++----------------
> fs/xfs/xfs_trans.c | 1 -
> 2 files changed, 42 insertions(+), 23 deletions(-)
>
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 6c4ab5e31054..4bcea22f7b3f 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -38,7 +38,7 @@ xfs_resizefs_init_new_ags(
> struct aghdr_init_data *id,
> xfs_agnumber_t oagcount,
> xfs_agnumber_t nagcount,
> - xfs_rfsblock_t *delta)
> + int64_t *delta)
> {
> xfs_rfsblock_t nb = mp->m_sb.sb_dblocks + *delta;
> int error;
> @@ -76,33 +76,41 @@ xfs_growfs_data_private(
> xfs_agnumber_t nagcount;
> xfs_agnumber_t nagimax = 0;
> xfs_rfsblock_t nb, nb_div, nb_mod;
> - xfs_rfsblock_t delta;
> + int64_t delta;
> xfs_agnumber_t oagcount;
> struct xfs_trans *tp;
> + bool extend;
> struct aghdr_init_data id = {};
>
> nb = in->newblocks;
> - if (nb < mp->m_sb.sb_dblocks)
> - return -EINVAL;
> - if ((error = xfs_sb_validate_fsb_count(&mp->m_sb, nb)))
> + if (nb == mp->m_sb.sb_dblocks)
> + return 0;
> +
> + error = xfs_sb_validate_fsb_count(&mp->m_sb, nb);
> + if (error)
> return error;
> - error = xfs_buf_read_uncached(mp->m_ddev_targp,
> +
> + if (nb > mp->m_sb.sb_dblocks) {
> + error = xfs_buf_read_uncached(mp->m_ddev_targp,
> XFS_FSB_TO_BB(mp, nb) - XFS_FSS_TO_BB(mp, 1),
> XFS_FSS_TO_BB(mp, 1), 0, &bp, NULL);
> - if (error)
> - return error;
> - xfs_buf_relse(bp);
> + if (error)
> + return error;
> + xfs_buf_relse(bp);
> + }
>
> nb_div = nb;
> nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
> nagcount = nb_div + (nb_mod != 0);
> 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)
> + if (nagcount < 2)
> return -EINVAL;
What's the reason for the nagcount < 2 check? IIRC we warn about this
configuration at mkfs time, but allow it to proceed. Is it just that we
don't want to accidentally put the fs into an agcount == 1 state that
was originally formatted with >1 AGs?
What about the case where we attempt to grow an agcount == 1 fs but
don't enlarge enough to add the second AG? Does this change error
behavior in that case?
> + nb = (xfs_rfsblock_t)nagcount * mp->m_sb.sb_agblocks;
> }
> +
> delta = nb - mp->m_sb.sb_dblocks;
> + extend = (delta > 0);
> oagcount = mp->m_sb.sb_agcount;
>
> /* allocate the new per-ag structures */
> @@ -110,22 +118,34 @@ 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);
> + (extend ? XFS_GROWFS_SPACE_RES(mp) : -delta), 0,
> + XFS_TRANS_RESERVE, &tp);
> if (error)
> return error;
>
> - error = xfs_resizefs_init_new_ags(mp, &id, oagcount, nagcount, &delta);
> - if (error)
> - goto out_trans_cancel;
> -
> + if (extend) {
> + error = xfs_resizefs_init_new_ags(mp, &id, oagcount,
> + nagcount, &delta);
> + if (error)
> + goto out_trans_cancel;
> + }
> xfs_trans_agblocks_delta(tp, id.nfree);
It looks like id isn't used until the resize call above. Is this call
relevant for the shrink case?
>
> - /* If there are new blocks in the old last AG, extend it. */
> + /* If there are some blocks in the last AG, resize it. */
> if (delta) {
This patch added a (nb == mp->m_sb.sb_dblocks) shortcut check at the top
of the function. Should we ever get to this point with delta == 0? (If
not, maybe convert it to an assert just to be safe.)
> - error = xfs_ag_extend_space(mp, tp, &id, delta);
> + if (extend) {
> + error = xfs_ag_extend_space(mp, tp, &id, delta);
> + } else {
> + id.agno = nagcount - 1;
> + error = xfs_ag_shrink_space(mp, &tp, &id, -delta);
xfs_ag_shrink_space() looks like it only accesses id->agno. Perhaps just
pass in agno for now..?
> + }
> +
> if (error)
> goto out_trans_cancel;
> }
> @@ -137,15 +157,15 @@ xfs_growfs_data_private(
> */
> if (nagcount > oagcount)
> xfs_trans_mod_sb(tp, XFS_TRANS_SB_AGCOUNT, nagcount - oagcount);
> - if (nb > mp->m_sb.sb_dblocks)
> + if (nb != mp->m_sb.sb_dblocks)
> xfs_trans_mod_sb(tp, XFS_TRANS_SB_DBLOCKS,
> nb - mp->m_sb.sb_dblocks);
Maybe use delta here?
> if (id.nfree)
> xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, id.nfree);
>
id.nfree tracks newly added free space in the growfs space. Is it not
used in the shrink case because the allocation handles this for us?
> /*
> - * update in-core counters now to reflect the real numbers
> - * (especially sb_fdblocks)
> + * update in-core counters now to reflect the real numbers (especially
> + * sb_fdblocks). And xfs_validate_sb_write() can pass for shrinkfs.
> */
> if (xfs_sb_version_haslazysbcount(&mp->m_sb))
> xfs_log_sb(tp);
> @@ -165,7 +185,7 @@ xfs_growfs_data_private(
> * If we expanded the last AG, free the per-AG reservation
> * so we can reinitialize it with the new size.
> */
> - if (delta) {
> + if (extend && delta) {
> struct xfs_perag *pag;
>
> pag = xfs_perag_get(mp, id.agno);
We call xfs_fs_reserve_ag_blocks() a bit further down before we exit
this function. xfs_ag_shrink_space() from the previous patch is intended
to deal with perag reservation changes for shrink, but it looks like the
reserve call further down could potentially reset mp->m_finobt_nores to
false if it previously might have been set to true.
Brian
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index e72730f85af1..fd2cbf414b80 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -419,7 +419,6 @@ 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
>
