xfs: introduce xfs_ag_shrink_space()

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.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index 9331f35..c68a366 100644 (file)
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -22,6 +22,11 @@
 #include "xfs_ag.h"
 #include "xfs_ag_resv.h"
 #include "xfs_health.h"
+#include "xfs_error.h"
+#include "xfs_bmap.h"
+#include "xfs_defer.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
 
 static int
 xfs_get_aghdr_buf(
@@ -485,6 +490,116 @@ 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;
+       /* some extra paranoid checks before we shrink the ag */
+       if (XFS_IS_CORRUPT(mp, agf->agf_length != agi->agi_length))
+               return -EFSCORRUPTED;
+       if (delta >= agi->agi_length)
+               return -EINVAL;
+
+       args.fsbno = XFS_AGB_TO_FSB(mp, agno,
+                                   be32_to_cpu(agi->agi_length) - delta);
+
+       /*
+        * Disable perag reservations so it doesn't cause the allocation request
+        * to fail. We'll reestablish reservation before we return.
+        */
+       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.
+                */
+               xfs_trans_bhold(*tpp, agfbp);
+               err2 = xfs_trans_roll(tpp);
+               if (err2)
+                       return err2;
+               xfs_trans_bjoin(*tpp, agfbp);
+               goto resv_init_out;
+       }
+
+       /*
+        * 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 5166322..4535de1 100644 (file)
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -24,6 +24,8 @@ 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 delta);
 int xfs_ag_extend_space(struct xfs_mount *mp, struct xfs_trans *tp,
                        struct aghdr_init_data *id, xfs_extlen_t len);
 int xfs_ag_get_geometry(struct xfs_mount *mp, xfs_agnumber_t agno,