On Tue, Jun 09, 2020 at 07:40:53PM +0800, Gao Xiang wrote: > In production, we found that sometimes xfs_repair phase 5 > rebuilds freespace node block with pointers less than minrecs > and if we trigger xfs_repair again it would report such > the following message: > > bad btree nrecs (39, min=40, max=80) in btbno block 0/7882 > > The background is that xfs_repair starts to rebuild AGFL > after the freespace btree is settled in phase 5 so we may > need to leave necessary room in advance for each btree > leaves in order to avoid freespace btree split and then > result in AGFL rebuild fails. The old mathematics uses > ceil(num_extents / maxrecs) to decide the number of node > blocks. That would be fine without leaving extra space > since minrecs = maxrecs / 2 but if some slack was decreased > from maxrecs, the result would be larger than what is > expected and cause num_recs_pb less than minrecs, i.e: > > num_extents = 79, adj_maxrecs = 80 - 2 (slack) = 78 > > so we'd get > > num_blocks = ceil(79 / 78) = 2, > num_recs_pb = 79 / 2 = 39, which is less than > minrecs = 80 / 2 = 40 > > OTOH, btree bulk loading code behaves in a different way. > As in xfs_btree_bload_level_geometry it wrote > > num_blocks = floor(num_extents / maxrecs) > > which will never go below minrecs. And when it goes > above maxrecs, just increment num_blocks and recalculate > so we can get the reasonable results. > > In the long term, btree bulk loader will replace the current > repair code as well as to resolve AGFL dependency issue. > But we may still want to look for a backportable solution > for stable versions. Hence, use the same logic to avoid the > freespace btree minrecs underflow for now. > > Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> > Cc: Dave Chinner <dchinner@xxxxxxxxxx> > Cc: Eric Sandeen <sandeen@xxxxxxxxxxx> > Fixes: 9851fd79bfb1 ("repair: AGFL rebuild fails if btree split required") > Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx> > --- > not heavy tested yet.. > > repair/phase5.c | 101 +++++++++++++++++++++--------------------------- > 1 file changed, 45 insertions(+), 56 deletions(-) > > diff --git a/repair/phase5.c b/repair/phase5.c > index abae8a08..997804a5 100644 > --- a/repair/phase5.c > +++ b/repair/phase5.c > @@ -348,11 +348,29 @@ finish_cursor(bt_status_t *curs) > * failure at runtime. Hence leave a couple of records slack space in > * each block to allow immediate modification of the tree without > * requiring splits to be done. > - * > - * XXX(hch): any reason we don't just look at mp->m_alloc_mxr? > */ > -#define XR_ALLOC_BLOCK_MAXRECS(mp, level) \ > - (libxfs_allocbt_maxrecs((mp), (mp)->m_sb.sb_blocksize, (level) == 0) - 2) > +static void > +compute_level_geometry(xfs_mount_t *mp, bt_stat_level_t *lptr, > + uint64_t nr_this_level, bool leaf) Please don't use structure typedefs here. Also, please indent the argument list like the rest of xfs code, e.g. static void compute_bnobt_geometry( struct xfs_mount *mp, struct bt_stat_level *lptr, (etc) > +{ > + unsigned int maxrecs = mp->m_alloc_mxr[!leaf]; > + int slack = leaf ? 2 : 0; > + unsigned int desired_npb; > + > + desired_npb = max(mp->m_alloc_mnr[!leaf], maxrecs - slack); > + lptr->num_recs_tot = nr_this_level; > + lptr->num_blocks = max(1ULL, nr_this_level / desired_npb); > + > + lptr->num_recs_pb = nr_this_level / lptr->num_blocks; > + lptr->modulo = nr_this_level % lptr->num_blocks; > + if (lptr->num_recs_pb > maxrecs || (lptr->num_recs_pb == maxrecs && > + lptr->modulo)) { Indentation.... if (lptr->num_recs_pb > maxrecs || (lptr->num_recs_pb == maxrecs && lptr->modulo)) { lptr->num_blocks++; ... } > + lptr->num_blocks++; > + > + lptr->num_recs_pb = nr_this_level / lptr->num_blocks; > + lptr->modulo = nr_this_level % lptr->num_blocks; > + } > +} > > /* > * this calculates a freespace cursor for an ag. > @@ -370,6 +388,7 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > int i; > int extents_used; > int extra_blocks; > + uint64_t old_blocks; > bt_stat_level_t *lptr; > bt_stat_level_t *p_lptr; > extent_tree_node_t *ext_ptr; > @@ -388,10 +407,7 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > * of the tree and set up the cursor for the leaf level > * (note that the same code is duplicated further down) > */ > - lptr->num_blocks = howmany(num_extents, XR_ALLOC_BLOCK_MAXRECS(mp, 0)); > - lptr->num_recs_pb = num_extents / lptr->num_blocks; > - lptr->modulo = num_extents % lptr->num_blocks; > - lptr->num_recs_tot = num_extents; > + compute_level_geometry(mp, lptr, num_extents, true); > level = 1; > > #ifdef XR_BLD_FREE_TRACE > @@ -406,18 +422,12 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > * per level is the # of blocks in the level below it > */ > if (lptr->num_blocks > 1) { > - for (; btree_curs->level[level - 1].num_blocks > 1 > - && level < XFS_BTREE_MAXLEVELS; > - level++) { > + do { > + p_lptr = lptr; > lptr = &btree_curs->level[level]; > - p_lptr = &btree_curs->level[level - 1]; > - lptr->num_blocks = howmany(p_lptr->num_blocks, > - XR_ALLOC_BLOCK_MAXRECS(mp, level)); > - lptr->modulo = p_lptr->num_blocks > - % lptr->num_blocks; > - lptr->num_recs_pb = p_lptr->num_blocks > - / lptr->num_blocks; > - lptr->num_recs_tot = p_lptr->num_blocks; > + > + compute_level_geometry(mp, lptr, > + p_lptr->num_blocks, false); > #ifdef XR_BLD_FREE_TRACE > fprintf(stderr, "%s %d %d %d %d %d\n", __func__, > level, > @@ -426,7 +436,9 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > lptr->modulo, > lptr->num_recs_tot); > #endif > - } > + level++; > + } while (lptr->num_blocks > 1); > + ASSERT (level < XFS_BTREE_MAXLEVELS); > } > > ASSERT(lptr->num_blocks == 1); > @@ -496,8 +508,11 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > * see if the number of leaf blocks will change as a result > * of the number of extents changing > */ > - if (howmany(num_extents, XR_ALLOC_BLOCK_MAXRECS(mp, 0)) > - != btree_curs->level[0].num_blocks) { > + old_blocks = btree_curs->level[0].num_blocks; > + compute_level_geometry(mp, &btree_curs->level[0], num_extents, true); > + extra_blocks = 0; > + > + if (old_blocks != btree_curs->level[0].num_blocks) { > /* > * yes -- recalculate the cursor. If the number of > * excess (overallocated) blocks is < xfs_agfl_size/2, we're ok. > @@ -553,30 +568,20 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > } > > lptr = &btree_curs->level[0]; > - lptr->num_blocks = howmany(num_extents, > - XR_ALLOC_BLOCK_MAXRECS(mp, 0)); > - lptr->num_recs_pb = num_extents / lptr->num_blocks; > - lptr->modulo = num_extents % lptr->num_blocks; > - lptr->num_recs_tot = num_extents; > level = 1; > > /* > * if we need more levels, set them up > */ > if (lptr->num_blocks > 1) { > - for (level = 1; btree_curs->level[level-1].num_blocks > - > 1 && level < XFS_BTREE_MAXLEVELS; > - level++) { > - lptr = &btree_curs->level[level]; > - p_lptr = &btree_curs->level[level-1]; > - lptr->num_blocks = howmany(p_lptr->num_blocks, > - XR_ALLOC_BLOCK_MAXRECS(mp, level)); > - lptr->modulo = p_lptr->num_blocks > - % lptr->num_blocks; > - lptr->num_recs_pb = p_lptr->num_blocks > - / lptr->num_blocks; > - lptr->num_recs_tot = p_lptr->num_blocks; > - } > + do { > + p_lptr = lptr; > + lptr = &btree_curs->level[level++]; > + > + compute_level_geometry(mp, lptr, > + p_lptr->num_blocks, false); > + } while (lptr->num_blocks > 1); /me wonders why it's necessary to wrap the do...while in an if test, as opposed to using a while loop with the if test up front? --D > + ASSERT (level < XFS_BTREE_MAXLEVELS); > } > ASSERT(lptr->num_blocks == 1); > btree_curs->num_levels = level; > @@ -591,22 +596,6 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno, > > ASSERT(blocks_allocated_total >= blocks_needed); > extra_blocks = blocks_allocated_total - blocks_needed; > - } else { > - if (extents_used > 0) { > - /* > - * reset the leaf level geometry to account > - * for consumed extents. we can leave the > - * rest of the cursor alone since the number > - * of leaf blocks hasn't changed. > - */ > - lptr = &btree_curs->level[0]; > - > - lptr->num_recs_pb = num_extents / lptr->num_blocks; > - lptr->modulo = num_extents % lptr->num_blocks; > - lptr->num_recs_tot = num_extents; > - } > - > - extra_blocks = 0; > } > > btree_curs->num_tot_blocks = blocks_allocated_pt; > -- > 2.18.1 >