bcachefs: Fix insufficient disk reservation with compression + snapshots

When overwriting and splitting existing extents, we weren't correctly
accounting for a 3 way split of a compressed extent.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/btree_update.c b/fs/bcachefs/btree_update.c
index 25fdca0..2fd3c8c 100644 (file)
--- a/fs/bcachefs/btree_update.c
+++ b/fs/bcachefs/btree_update.c
@@ -186,8 +186,11 @@ int bch2_trans_update_extent_overwrite(struct btree_trans *trans,
        enum btree_id btree_id = iter->btree_id;
        struct bkey_i *update;
        struct bpos new_start = bkey_start_pos(new.k);
-       bool front_split = bkey_lt(bkey_start_pos(old.k), new_start);
-       bool back_split  = bkey_gt(old.k->p, new.k->p);
+       unsigned front_split = bkey_lt(bkey_start_pos(old.k), new_start);
+       unsigned back_split  = bkey_gt(old.k->p, new.k->p);
+       unsigned middle_split = (front_split || back_split) &&
+               old.k->p.snapshot != new.k->p.snapshot;
+       unsigned nr_splits = front_split + back_split + middle_split;
        int ret = 0, compressed_sectors;
 
        /*
@@ -195,10 +198,9 @@ int bch2_trans_update_extent_overwrite(struct btree_trans *trans,
         * so that __bch2_trans_commit() can increase our disk
         * reservation:
         */
-       if (((front_split && back_split) ||
-            ((front_split || back_split) && old.k->p.snapshot != new.k->p.snapshot)) &&
+       if (nr_splits > 1 &&
            (compressed_sectors = bch2_bkey_sectors_compressed(old)))
-               trans->extra_journal_res += compressed_sectors;
+               trans->extra_journal_res += compressed_sectors * (nr_splits - 1);
 
        if (front_split) {
                update = bch2_bkey_make_mut_noupdate(trans, old);
@@ -216,8 +218,7 @@ int bch2_trans_update_extent_overwrite(struct btree_trans *trans,
        }
 
        /* If we're overwriting in a different snapshot - middle split: */
-       if (old.k->p.snapshot != new.k->p.snapshot &&
-           (front_split || back_split)) {
+       if (middle_split) {
                update = bch2_bkey_make_mut_noupdate(trans, old);
                if ((ret = PTR_ERR_OR_ZERO(update)))
                        return ret;