bcachefs: Don't keep tons of cached pointers around

We had a bug report where the data update path was creating an extent
that failed to validate because it had too many pointers; almost all of
them were cached.

To fix this, we have:
- want_cached_ptr(), a new helper that checks if we even want a cached
  pointer (is on appropriate target, device is readable).

- bch2_extent_set_ptr_cached() now only sets a pointer cached if we want
  it.

- bch2_extent_normalize_by_opts() now ensures that we only have a single
  cached pointer that we want.

While working on this, it was noticed that this doesn't work well with
reflinked data and per-file options. Another patch series is coming that
plumbs through additional io path options through bch_extent_rebalance,
with improved option handling.

Reported-by: Reed Riley <reed@riley.engineer>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/data_update.c

@@ -236,7 +236,8 @@ static int __bch2_data_update_index_update(struct btree_trans *trans,
 			if (((1U << i) & m->data_opts.rewrite_ptrs) &&
 			    (ptr = bch2_extent_has_ptr(old, p, bkey_i_to_s(insert))) &&
 			    !ptr->cached) {
-				bch2_extent_ptr_set_cached(bkey_i_to_s(insert), ptr);
+				bch2_extent_ptr_set_cached(c, &m->op.opts,
+							   bkey_i_to_s(insert), ptr);
 				rewrites_found |= 1U << i;
 			}
 			i++;
@@ -284,7 +285,8 @@ restart_drop_extra_replicas:
 			    durability - ptr_durability >= m->op.opts.data_replicas) {
 				durability -= ptr_durability;
 
-				bch2_extent_ptr_set_cached(bkey_i_to_s(insert), &entry->ptr);
+				bch2_extent_ptr_set_cached(c, &m->op.opts,
+							   bkey_i_to_s(insert), &entry->ptr);
 				goto restart_drop_extra_replicas;
 			}
 		}
@@ -295,7 +297,7 @@ restart_drop_extra_replicas:
 			bch2_extent_ptr_decoded_append(insert, &p);
 
 		bch2_bkey_narrow_crcs(insert, (struct bch_extent_crc_unpacked) { 0 });
-		bch2_extent_normalize(c, bkey_i_to_s(insert));
+		bch2_extent_normalize_by_opts(c, &m->op.opts, bkey_i_to_s(insert));
 
 		ret = bch2_sum_sector_overwrites(trans, &iter, insert,
 						 &should_check_enospc,
@@ -558,7 +560,8 @@ void bch2_data_update_to_text(struct printbuf *out, struct data_update *m)
 int bch2_extent_drop_ptrs(struct btree_trans *trans,
 			  struct btree_iter *iter,
 			  struct bkey_s_c k,
-			  struct data_update_opts data_opts)
+			  struct bch_io_opts *io_opts,
+			  struct data_update_opts *data_opts)
 {
 	struct bch_fs *c = trans->c;
 	struct bkey_i *n;
@@ -569,11 +572,11 @@ int bch2_extent_drop_ptrs(struct btree_trans *trans,
 	if (ret)
 		return ret;
 
-	while (data_opts.kill_ptrs) {
-		unsigned i = 0, drop = __fls(data_opts.kill_ptrs);
+	while (data_opts->kill_ptrs) {
+		unsigned i = 0, drop = __fls(data_opts->kill_ptrs);
 
 		bch2_bkey_drop_ptrs_noerror(bkey_i_to_s(n), ptr, i++ == drop);
-		data_opts.kill_ptrs ^= 1U << drop;
+		data_opts->kill_ptrs ^= 1U << drop;
 	}
 
 	/*
@@ -581,7 +584,7 @@ int bch2_extent_drop_ptrs(struct btree_trans *trans,
 	 * will do the appropriate thing with it (turning it into a
 	 * KEY_TYPE_error key, or just a discard if it was a cached extent)
 	 */
-	bch2_extent_normalize(c, bkey_i_to_s(n));
+	bch2_extent_normalize_by_opts(c, io_opts, bkey_i_to_s(n));
 
 	/*
 	 * Since we're not inserting through an extent iterator
@@ -720,7 +723,7 @@ int bch2_data_update_init(struct btree_trans *trans,
 		m->data_opts.rewrite_ptrs = 0;
 		/* if iter == NULL, it's just a promote */
 		if (iter)
-			ret = bch2_extent_drop_ptrs(trans, iter, k, m->data_opts);
+			ret = bch2_extent_drop_ptrs(trans, iter, k, &io_opts, &m->data_opts);
 		goto out;
 	}
 

fs/bcachefs/data_update.h

@@ -40,7 +40,8 @@ void bch2_data_update_read_done(struct data_update *,
 int bch2_extent_drop_ptrs(struct btree_trans *,
 			  struct btree_iter *,
 			  struct bkey_s_c,
-			  struct data_update_opts);
+			  struct bch_io_opts *,
+			  struct data_update_opts *);
 
 void bch2_data_update_exit(struct data_update *);
 int bch2_data_update_init(struct btree_trans *, struct btree_iter *,

fs/bcachefs/extents.c

@@ -978,31 +978,54 @@ bch2_extent_has_ptr(struct bkey_s_c k1, struct extent_ptr_decoded p1, struct bke
 	return NULL;
 }
 
-void bch2_extent_ptr_set_cached(struct bkey_s k, struct bch_extent_ptr *ptr)
+static bool want_cached_ptr(struct bch_fs *c, struct bch_io_opts *opts,
+			    struct bch_extent_ptr *ptr)
+{
+	if (!opts->promote_target ||
+	    !bch2_dev_in_target(c, ptr->dev, opts->promote_target))
+		return false;
+
+	struct bch_dev *ca = bch2_dev_rcu_noerror(c, ptr->dev);
+
+	return ca && bch2_dev_is_readable(ca) && !dev_ptr_stale_rcu(ca, ptr);
+}
+
+void bch2_extent_ptr_set_cached(struct bch_fs *c,
+				struct bch_io_opts *opts,
+				struct bkey_s k,
+				struct bch_extent_ptr *ptr)
 {
 	struct bkey_ptrs ptrs = bch2_bkey_ptrs(k);
 	union bch_extent_entry *entry;
-	union bch_extent_entry *ec = NULL;
+	struct extent_ptr_decoded p;
 
-	bkey_extent_entry_for_each(ptrs, entry) {
-		if (&entry->ptr == ptr) {
-			ptr->cached = true;
-			if (ec)
-				extent_entry_drop(k, ec);
-			return;
-		}
-
-		if (extent_entry_is_stripe_ptr(entry))
-			ec = entry;
-		else if (extent_entry_is_ptr(entry))
-			ec = NULL;
-	}
-
-	BUG();
+	rcu_read_lock();
+	if (!want_cached_ptr(c, opts, ptr)) {
+		bch2_bkey_drop_ptr_noerror(k, ptr);
+		goto out;
 	}
 
 	/*
- * bch_extent_normalize - clean up an extent, dropping stale pointers etc.
+	 * Stripes can't contain cached data, for - reasons.
+	 *
+	 * Possibly something we can fix in the future?
+	 */
+	bkey_for_each_ptr_decode(k.k, ptrs, p, entry)
+		if (&entry->ptr == ptr) {
+			if (p.has_ec)
+				bch2_bkey_drop_ptr_noerror(k, ptr);
+			else
+				ptr->cached = true;
+			goto out;
+		}
+
+	BUG();
+out:
+	rcu_read_unlock();
+}
+
+/*
+ * bch2_extent_normalize - clean up an extent, dropping stale pointers etc.
  *
  * Returns true if @k should be dropped entirely
  *
@@ -1016,8 +1039,39 @@ bool bch2_extent_normalize(struct bch_fs *c, struct bkey_s k)
 	rcu_read_lock();
 	bch2_bkey_drop_ptrs(k, ptr,
 		ptr->cached &&
-		(ca = bch2_dev_rcu(c, ptr->dev)) &&
-		dev_ptr_stale_rcu(ca, ptr) > 0);
+		(!(ca = bch2_dev_rcu(c, ptr->dev)) ||
+		 dev_ptr_stale_rcu(ca, ptr) > 0));
+	rcu_read_unlock();
+
+	return bkey_deleted(k.k);
+}
+
+/*
+ * bch2_extent_normalize_by_opts - clean up an extent, dropping stale pointers etc.
+ *
+ * Like bch2_extent_normalize(), but also only keeps a single cached pointer on
+ * the promote target.
+ */
+bool bch2_extent_normalize_by_opts(struct bch_fs *c,
+				   struct bch_io_opts *opts,
+				   struct bkey_s k)
+{
+	struct bkey_ptrs ptrs;
+	bool have_cached_ptr;
+
+	rcu_read_lock();
+restart_drop_ptrs:
+	ptrs = bch2_bkey_ptrs(k);
+	have_cached_ptr = false;
+
+	bkey_for_each_ptr(ptrs, ptr)
+		if (ptr->cached) {
+			if (have_cached_ptr || !want_cached_ptr(c, opts, ptr)) {
+				bch2_bkey_drop_ptr(k, ptr);
+				goto restart_drop_ptrs;
+			}
+			have_cached_ptr = true;
+		}
 	rcu_read_unlock();
 
 	return bkey_deleted(k.k);

fs/bcachefs/extents.h

@@ -686,9 +686,12 @@ bool bch2_extents_match(struct bkey_s_c, struct bkey_s_c);
 struct bch_extent_ptr *
 bch2_extent_has_ptr(struct bkey_s_c, struct extent_ptr_decoded, struct bkey_s);
 
-void bch2_extent_ptr_set_cached(struct bkey_s, struct bch_extent_ptr *);
+void bch2_extent_ptr_set_cached(struct bch_fs *, struct bch_io_opts *,
+				struct bkey_s, struct bch_extent_ptr *);
 
+bool bch2_extent_normalize_by_opts(struct bch_fs *, struct bch_io_opts *, struct bkey_s);
 bool bch2_extent_normalize(struct bch_fs *, struct bkey_s);
+
 void bch2_extent_ptr_to_text(struct printbuf *out, struct bch_fs *, const struct bch_extent_ptr *);
 void bch2_bkey_ptrs_to_text(struct printbuf *, struct bch_fs *,
 			    struct bkey_s_c);

fs/bcachefs/move.c

@@ -266,7 +266,7 @@ int bch2_move_extent(struct moving_context *ctxt,
 	if (!data_opts.rewrite_ptrs &&
 	    !data_opts.extra_replicas) {
 		if (data_opts.kill_ptrs)
-			return bch2_extent_drop_ptrs(trans, iter, k, data_opts);
+			return bch2_extent_drop_ptrs(trans, iter, k, &io_opts, &data_opts);
 		return 0;
 	}