On Wed, Jun 10, 2020 at 01:26:24PM +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.
>
> Later, btree bulk loader will replace the current repair code.
> But we may still want to look for a backportable solution
> for stable versions. Hence, keep the same logic to avoid
> the freespace as well as rmap 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>
> ---
> changes since v2:
> still some minor styling fix (ASSERT, args)..
>
> changes since v1:
> - fix indentation, typedefs, etc code styling problem
> pointed out by Darrick;
>
> - adapt init_rmapbt_cursor to the new algorithm since
> it's similar pointed out by Darrick; thus the function
> name remains the origin compute_level_geometry...
> and hence, adjust the subject a bit as well.
>
> repair/phase5.c | 152 ++++++++++++++++++++----------------------------
> 1 file changed, 63 insertions(+), 89 deletions(-)
>
> diff --git a/repair/phase5.c b/repair/phase5.c
> index abae8a08..d30d32b2 100644
> --- a/repair/phase5.c
> +++ b/repair/phase5.c
> @@ -348,11 +348,32 @@ 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(
> + struct xfs_mount *mp,
> + struct bt_stat_level *lptr,
> + uint64_t nr_this_level,
Probably didn't need a u64 here, but <shrug> that's probably just my
kernel-coloured glasses. :)
> + int slack,
> + bool leaf)
> +{
> + unsigned int maxrecs = mp->m_alloc_mxr[!leaf];
> + 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)) {
> + lptr->num_blocks++;
> +
> + lptr->num_recs_pb = nr_this_level / lptr->num_blocks;
> + lptr->modulo = nr_this_level % lptr->num_blocks;
> + }
Seems to be more or less the same solution that I (half unknowingly)
coded into the btree bulkload geometry calculator, so:
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
(Still working on adapting the new phase5 code to try to fill the AGFL
as part of rebuilding the free space btrees, fwiw.)
--D
> +}
>
> /*
> * this calculates a freespace cursor for an ag.
> @@ -370,6 +391,7 @@ 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 +410,7 @@ 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, 2, true);
> level = 1;
>
> #ifdef XR_BLD_FREE_TRACE
> @@ -405,30 +424,23 @@ calculate_freespace_cursor(xfs_mount_t *mp, xfs_agnumber_t agno,
> * if we need more levels, set them up. # of records
> * 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++) {
> - 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;
> + while (lptr->num_blocks > 1) {
> + p_lptr = lptr;
> + lptr = &btree_curs->level[level];
> +
> + compute_level_geometry(mp, lptr,
> + p_lptr->num_blocks, 0, false);
> #ifdef XR_BLD_FREE_TRACE
> - fprintf(stderr, "%s %d %d %d %d %d\n", __func__,
> - level,
> - lptr->num_blocks,
> - lptr->num_recs_pb,
> - lptr->modulo,
> - lptr->num_recs_tot);
> + fprintf(stderr, "%s %d %d %d %d %d\n", __func__,
> + level,
> + lptr->num_blocks,
> + lptr->num_recs_pb,
> + lptr->modulo,
> + lptr->num_recs_tot);
> #endif
> - }
> + level++;
> }
> -
> + ASSERT(level < XFS_BTREE_MAXLEVELS);
> ASSERT(lptr->num_blocks == 1);
> btree_curs->num_levels = level;
>
> @@ -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, 2, 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.
> @@ -553,31 +568,19 @@ 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;
> - }
> + while (lptr->num_blocks > 1) {
> + p_lptr = lptr;
> + lptr = &btree_curs->level[level++];
> +
> + compute_level_geometry(mp, lptr,
> + p_lptr->num_blocks, 0, false);
> }
> + ASSERT(level < XFS_BTREE_MAXLEVELS);
> ASSERT(lptr->num_blocks == 1);
> btree_curs->num_levels = level;
>
> @@ -591,22 +594,6 @@ 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;
> @@ -1376,7 +1363,6 @@ init_rmapbt_cursor(
> struct bt_stat_level *lptr;
> struct bt_stat_level *p_lptr;
> xfs_extlen_t blocks_allocated;
> - int maxrecs;
>
> if (!xfs_sb_version_hasrmapbt(&mp->m_sb)) {
> memset(btree_curs, 0, sizeof(struct bt_status));
> @@ -1412,32 +1398,20 @@ init_rmapbt_cursor(
> * Leave enough slack in the rmapbt that we can insert the
> * metadata AG entries without too many splits.
> */
> - maxrecs = mp->m_rmap_mxr[0];
> - if (num_recs > maxrecs)
> - maxrecs -= 10;
> - blocks_allocated = lptr->num_blocks = howmany(num_recs, maxrecs);
> -
> - lptr->modulo = num_recs % lptr->num_blocks;
> - lptr->num_recs_pb = num_recs / lptr->num_blocks;
> - lptr->num_recs_tot = num_recs;
> + compute_level_geometry(mp, lptr, num_recs,
> + num_recs > mp->m_rmap_mxr[0] ? 10 : 0, true);
> + blocks_allocated = lptr->num_blocks;
> level = 1;
>
> - if (lptr->num_blocks > 1) {
> - for (; 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,
> - mp->m_rmap_mxr[1]);
> - 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;
> + while (lptr->num_blocks > 1) {
> + p_lptr = lptr;
> + lptr = &btree_curs->level[level++];
>
> - blocks_allocated += lptr->num_blocks;
> - }
> + compute_level_geometry(mp, lptr,
> + p_lptr->num_blocks, 0, false);
> + blocks_allocated += lptr->num_blocks;
> }
> + ASSERT(level < XFS_BTREE_MAXLEVELS);
> ASSERT(lptr->num_blocks == 1);
> btree_curs->num_levels = level;
>
> --
> 2.18.1
>
