xfs: use per-AG reservations for the finobt

Currently we try to rely on the global reserved block pool for block
allocations for the free inode btree, but I have customer reports
(fairly complex workload, need to find an easier reproducer) where that
is not enough as the AG where we free an inode that requires a new
finobt block is entirely full.  This causes us to cancel a dirty
transaction and thus a file system shutdown.

I think the right way to guard against this is to treat the finot the same
way as the refcount btree and have a per-AG reservations for the possible
worst case size of it, and the patch below implements that.

Note that this could increase mount times with large finobt trees.  In
an ideal world we would have added a field for the number of finobt
fields to the AGI, similar to what we did for the refcount blocks.
We should do add it next time we rev the AGI or AGF format by adding
new fields.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

5 files changed, 144 insertions, 20 deletions

diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
index 94234bff40dc..33db69be4832 100644
--- a/fs/xfs/libxfs/xfs_ag_resv.c
+++ b/fs/xfs/libxfs/xfs_ag_resv.c
@@ -39,6 +39,7 @@
 #include "xfs_rmap_btree.h"
 #include "xfs_btree.h"
 #include "xfs_refcount_btree.h"
+#include "xfs_ialloc_btree.h"
 
 /*
  * Per-AG Block Reservations
@@ -210,6 +211,9 @@ __xfs_ag_resv_init(
         if (error) {
                 trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
                                 error, _RET_IP_);
+                xfs_warn(mp,
+"Per-AG reservation for AG %u failed.  Filesystem may run out of space.",
+                                pag->pag_agno);
                 return error;
         }
 
@@ -228,6 +232,8 @@ int
 xfs_ag_resv_init(
         struct xfs_perag                *pag)
 {
+        struct xfs_mount                *mp = pag->pag_mount;
+        xfs_agnumber_t                  agno = pag->pag_agno;
         xfs_extlen_t                    ask;
         xfs_extlen_t                    used;
         int                             error = 0;
@@ -236,23 +242,45 @@ xfs_ag_resv_init(
         if (pag->pag_meta_resv.ar_asked == 0) {
                 ask = used = 0;
 
-                error = xfs_refcountbt_calc_reserves(pag->pag_mount,
-                                pag->pag_agno, &ask, &used);
+                error = xfs_refcountbt_calc_reserves(mp, agno, &ask, &used);
                 if (error)
                         goto out;
 
-                error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
-                                ask, used);
+                error = xfs_finobt_calc_reserves(mp, agno, &ask, &used);
                 if (error)
                         goto out;
+
+                error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
+                                ask, used);
+                if (error) {
+                        /*
+                         * Because we didn't have per-AG reservations when the
+                         * finobt feature was added we might not be able to
+                         * reserve all needed blocks.  Warn and fall back to the
+                         * old and potentially buggy code in that case, but
+                         * ensure we do have the reservation for the refcountbt.
+                         */
+                        ask = used = 0;
+
+                        mp->m_inotbt_nores = true;
+
+                        error = xfs_refcountbt_calc_reserves(mp, agno, &ask,
+                                        &used);
+                        if (error)
+                                goto out;
+
+                        error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
+                                        ask, used);
+                        if (error)
+                                goto out;
+                }
         }
 
         /* Create the AGFL metadata reservation */
         if (pag->pag_agfl_resv.ar_asked == 0) {
                 ask = used = 0;
 
-                error = xfs_rmapbt_calc_reserves(pag->pag_mount, pag->pag_agno,
-                                &ask, &used);
+                error = xfs_rmapbt_calc_reserves(mp, agno, &ask, &used);
                 if (error)
                         goto out;
 
@@ -261,9 +289,16 @@ xfs_ag_resv_init(
                         goto out;
         }
 
+#ifdef DEBUG
+        /* need to read in the AGF for the ASSERT below to work */
+        error = xfs_alloc_pagf_init(pag->pag_mount, NULL, pag->pag_agno, 0);
+        if (error)
+                return error;
+
         ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
                xfs_perag_resv(pag, XFS_AG_RESV_AGFL)->ar_reserved <=
                pag->pagf_freeblks + pag->pagf_flcount);
+#endif
 out:
         return error;
 }
diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
index 0fd086d03d41..7c471881c9a6 100644
--- a/fs/xfs/libxfs/xfs_ialloc_btree.c
+++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
@@ -82,11 +82,12 @@ xfs_finobt_set_root(
 }
 
 STATIC int
-xfs_inobt_alloc_block(
+__xfs_inobt_alloc_block(
         struct xfs_btree_cur    *cur,
         union xfs_btree_ptr     *start,
         union xfs_btree_ptr     *new,
-        int                     *stat)
+        int                     *stat,
+        enum xfs_ag_resv_type   resv)
 {
         xfs_alloc_arg_t         args;           /* block allocation args */
         int                     error;          /* error return value */
@@ -103,6 +104,7 @@ xfs_inobt_alloc_block(
         args.maxlen = 1;
         args.prod = 1;
         args.type = XFS_ALLOCTYPE_NEAR_BNO;
+        args.resv = resv;
 
         error = xfs_alloc_vextent(&args);
         if (error) {
@@ -123,6 +125,27 @@ xfs_inobt_alloc_block(
 }
 
 STATIC int
+xfs_inobt_alloc_block(
+        struct xfs_btree_cur    *cur,
+        union xfs_btree_ptr     *start,
+        union xfs_btree_ptr     *new,
+        int                     *stat)
+{
+        return __xfs_inobt_alloc_block(cur, start, new, stat, XFS_AG_RESV_NONE);
+}
+
+STATIC int
+xfs_finobt_alloc_block(
+        struct xfs_btree_cur    *cur,
+        union xfs_btree_ptr     *start,
+        union xfs_btree_ptr     *new,
+        int                     *stat)
+{
+        return __xfs_inobt_alloc_block(cur, start, new, stat,
+                        XFS_AG_RESV_METADATA);
+}
+
+STATIC int
 xfs_inobt_free_block(
         struct xfs_btree_cur    *cur,
         struct xfs_buf          *bp)
@@ -328,7 +351,7 @@ static const struct xfs_btree_ops xfs_finobt_ops = {
 
         .dup_cursor             = xfs_inobt_dup_cursor,
         .set_root               = xfs_finobt_set_root,
-        .alloc_block            = xfs_inobt_alloc_block,
+        .alloc_block            = xfs_finobt_alloc_block,
         .free_block             = xfs_inobt_free_block,
         .get_minrecs            = xfs_inobt_get_minrecs,
         .get_maxrecs            = xfs_inobt_get_maxrecs,
@@ -480,3 +503,64 @@ xfs_inobt_rec_check_count(
         return 0;
 }
 #endif  /* DEBUG */
+
+static xfs_extlen_t
+xfs_inobt_max_size(
+        struct xfs_mount        *mp)
+{
+        /* Bail out if we're uninitialized, which can happen in mkfs. */
+        if (mp->m_inobt_mxr[0] == 0)
+                return 0;
+
+        return xfs_btree_calc_size(mp, mp->m_inobt_mnr,
+                (uint64_t)mp->m_sb.sb_agblocks * mp->m_sb.sb_inopblock /
+                                XFS_INODES_PER_CHUNK);
+}
+
+static int
+xfs_inobt_count_blocks(
+        struct xfs_mount        *mp,
+        xfs_agnumber_t          agno,
+        xfs_btnum_t             btnum,
+        xfs_extlen_t            *tree_blocks)
+{
+        struct xfs_buf          *agbp;
+        struct xfs_btree_cur    *cur;
+        int                     error;
+
+        error = xfs_ialloc_read_agi(mp, NULL, agno, &agbp);
+        if (error)
+                return error;
+
+        cur = xfs_inobt_init_cursor(mp, NULL, agbp, agno, btnum);
+        error = xfs_btree_count_blocks(cur, tree_blocks);
+        xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);
+        xfs_buf_relse(agbp);
+
+        return error;
+}
+
+/*
+ * Figure out how many blocks to reserve and how many are used by this btree.
+ */
+int
+xfs_finobt_calc_reserves(
+        struct xfs_mount        *mp,
+        xfs_agnumber_t          agno,
+        xfs_extlen_t            *ask,
+        xfs_extlen_t            *used)
+{
+        xfs_extlen_t            tree_len = 0;
+        int                     error;
+
+        if (!xfs_sb_version_hasfinobt(&mp->m_sb))
+                return 0;
+
+        error = xfs_inobt_count_blocks(mp, agno, XFS_BTNUM_FINO, &tree_len);
+        if (error)
+                return error;
+
+        *ask += xfs_inobt_max_size(mp);
+        *used += tree_len;
+        return 0;
+}
diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.h b/fs/xfs/libxfs/xfs_ialloc_btree.h
index bd88453217ce..aa81e2e63f3f 100644
--- a/fs/xfs/libxfs/xfs_ialloc_btree.h
+++ b/fs/xfs/libxfs/xfs_ialloc_btree.h
@@ -72,4 +72,7 @@ int xfs_inobt_rec_check_count(struct xfs_mount *,
 #define xfs_inobt_rec_check_count(mp, rec)      0
 #endif  /* DEBUG */
 
+int xfs_finobt_calc_reserves(struct xfs_mount *mp, xfs_agnumber_t agno,
+                xfs_extlen_t *ask, xfs_extlen_t *used);
+
 #endif  /* __XFS_IALLOC_BTREE_H__ */
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index b9557795eb74..de32f0fe47c8 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1792,22 +1792,23 @@ xfs_inactive_ifree(
         int                     error;
 
         /*
-         * The ifree transaction might need to allocate blocks for record
-         * insertion to the finobt. We don't want to fail here at ENOSPC, so
-         * allow ifree to dip into the reserved block pool if necessary.
-         *
-         * Freeing large sets of inodes generally means freeing inode chunks,
-         * directory and file data blocks, so this should be relatively safe.
-         * Only under severe circumstances should it be possible to free enough
-         * inodes to exhaust the reserve block pool via finobt expansion while
-         * at the same time not creating free space in the filesystem.
+         * We try to use a per-AG reservation for any block needed by the finobt
+         * tree, but as the finobt feature predates the per-AG reservation
+         * support a degraded file system might not have enough space for the
+         * reservation at mount time.  In that case try to dip into the reserved
+         * pool and pray.
          *
          * Send a warning if the reservation does happen to fail, as the inode
          * now remains allocated and sits on the unlinked list until the fs is
          * repaired.
          */
-        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ifree,
-                        XFS_IFREE_SPACE_RES(mp), 0, XFS_TRANS_RESERVE, &tp);
+        if (unlikely(mp->m_inotbt_nores)) {
+                error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ifree,
+                                XFS_IFREE_SPACE_RES(mp), 0, XFS_TRANS_RESERVE,
+                                &tp);
+        } else {
+                error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ifree, 0, 0, 0, &tp);
+        }
         if (error) {
                 if (error == -ENOSPC) {
                         xfs_warn_ratelimited(mp,
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 84f785218907..7f351f706b7a 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -140,6 +140,7 @@ typedef struct xfs_mount {
         int                     m_fixedfsid[2]; /* unchanged for life of FS */
         uint                    m_dmevmask;     /* DMI events for this FS */
         __uint64_t              m_flags;        /* global mount flags */
+        bool                    m_inotbt_nores; /* no per-AG finobt resv. */
         int                     m_ialloc_inos;  /* inodes in inode allocation */
         int                     m_ialloc_blks;  /* blocks in inode allocation */
         int                     m_ialloc_min_blks;/* min blocks in sparse inode