bcachefs: Run bch2_check_backpointers_to_extents() in multiple passes if necessary

When the extents + reflink btrees don't fit into memory this fsck pass
becomes _much_ slower, since we're doing random lookups.

This patch changes this pass to check how much of the relevant btrees
will fit into memory, and run in multiple passes if needed.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/backpointers.c

 // SPDX-License-Identifier: GPL-2.0
 #include "bcachefs.h"
+#include "bbpos.h"
 #include "alloc_background.h"
 #include "backpointers.h"
 #include "btree_cache.h"
 #include "btree_update.h"
 #include "error.h"
 
+#include <linux/mm.h>
+
 static bool extent_matches_bp(struct bch_fs *c,
 			      enum btree_id btree_id, unsigned level,
 			      struct bkey_s_c k,
@@ -693,6 +696,71 @@ static int check_btree_root_to_backpointers(struct btree_trans *trans,
 	return ret;
 }
 
+static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
+{
+	return (struct bbpos) {
+		.btree	= bp.btree_id,
+		.pos	= bp.pos,
+	};
+}
+
+static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
+{
+	struct sysinfo i;
+	u64 mem_bytes;
+
+	si_meminfo(&i);
+	mem_bytes = i.totalram * i.mem_unit;
+	return (mem_bytes >> 1) / btree_bytes(c);
+}
+
+int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
+				 unsigned btree_leaf_mask,
+				 unsigned btree_interior_mask,
+				 struct bbpos start, struct bbpos *end)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
+	enum btree_id btree;
+	int ret = 0;
+
+	for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
+		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;
+
+		if (!((1U << btree) & btree_leaf_mask) &&
+		    !((1U << btree) & btree_interior_mask))
+			continue;
+
+		bch2_trans_node_iter_init(trans, &iter, btree,
+					  btree == start.btree ? start.pos : POS_MIN,
+					  0, depth, 0);
+		/*
+		 * for_each_btree_key_contineu() doesn't check the return value
+		 * from bch2_btree_iter_advance(), which is needed when
+		 * iterating over interior nodes where we'll see keys at
+		 * SPOS_MAX:
+		 */
+		do {
+			k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
+			ret = bkey_err(k);
+			if (!k.k || ret)
+				break;
+
+			--btree_nodes;
+			if (!btree_nodes) {
+				*end = BBPOS(btree, k.k->p);
+				bch2_trans_iter_exit(trans, &iter);
+				return 0;
+			}
+		} while (bch2_btree_iter_advance(&iter));
+		bch2_trans_iter_exit(trans, &iter);
+	}
+
+	*end = BBPOS_MAX;
+	return ret;
+}
+
 int bch2_check_extents_to_backpointers(struct bch_fs *c)
 {
 	struct btree_trans trans;
@@ -736,19 +804,26 @@ int bch2_check_extents_to_backpointers(struct bch_fs *c)
 
 static int check_one_backpointer(struct btree_trans *trans,
 				 struct bpos bucket,
-				 u64 *bp_offset)
+				 u64 *bp_offset,
+				 struct bbpos start,
+				 struct bbpos end)
 {
 	struct btree_iter iter;
 	struct bch_backpointer bp;
+	struct bbpos pos;
 	struct bkey_s_c k;
 	struct printbuf buf = PRINTBUF;
 	int ret;
 
-	ret = bch2_get_next_backpointer(trans, bucket, -1,
-					bp_offset, &bp);
+	ret = bch2_get_next_backpointer(trans, bucket, -1, bp_offset, &bp);
 	if (ret || *bp_offset == U64_MAX)
 		return ret;
 
+	pos = bp_to_bbpos(bp);
+	if (bbpos_cmp(pos, start) < 0 ||
+	    bbpos_cmp(pos, end) > 0)
+		return 0;
+
 	k = bch2_backpointer_get_key(trans, &iter, bucket, *bp_offset, bp);
 	ret = bkey_err(k);
 	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
@@ -771,29 +846,73 @@ static int check_one_backpointer(struct btree_trans *trans,
 	return ret;
 }
 
-int bch2_check_backpointers_to_extents(struct bch_fs *c)
+static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
+						   struct bbpos start,
+						   struct bbpos end)
 {
-	struct btree_trans trans;
 	struct btree_iter iter;
 	struct bkey_s_c k;
 	int ret = 0;
 
-	bch2_trans_init(&trans, c, 0, 0);
-	for_each_btree_key(&trans, iter, BTREE_ID_alloc, POS_MIN,
+	for_each_btree_key(trans, iter, BTREE_ID_alloc, POS_MIN,
 			   BTREE_ITER_PREFETCH, k, ret) {
 		u64 bp_offset = 0;
 
-		while (!(ret = commit_do(&trans, NULL, NULL,
-					       BTREE_INSERT_LAZY_RW|
-					       BTREE_INSERT_NOFAIL,
-				check_one_backpointer(&trans, iter.pos, &bp_offset))) &&
+		while (!(ret = commit_do(trans, NULL, NULL,
+					 BTREE_INSERT_LAZY_RW|
+					 BTREE_INSERT_NOFAIL,
+				check_one_backpointer(trans, iter.pos, &bp_offset, start, end))) &&
 		       bp_offset < U64_MAX)
 			bp_offset++;
 
 		if (ret)
 			break;
 	}
-	bch2_trans_iter_exit(&trans, &iter);
-	bch2_trans_exit(&trans);
+	bch2_trans_iter_exit(trans, &iter);
 	return ret < 0 ? ret : 0;
 }
+
+int bch2_check_backpointers_to_extents(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
+	int ret;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	while (1) {
+		ret = bch2_get_btree_in_memory_pos(&trans,
+						   (1U << BTREE_ID_extents)|
+						   (1U << BTREE_ID_reflink),
+						   ~0,
+						   start, &end);
+		if (ret)
+			break;
+
+		if (!bbpos_cmp(start, BBPOS_MIN) &&
+		    bbpos_cmp(end, BBPOS_MAX))
+			bch_verbose(c, "%s(): extents do not fit in ram, running in multiple passes with %zu nodes per pass",
+				    __func__, btree_nodes_fit_in_ram(c));
+
+		if (bbpos_cmp(start, BBPOS_MIN) ||
+		    bbpos_cmp(end, BBPOS_MAX)) {
+			struct printbuf buf = PRINTBUF;
+
+			prt_str(&buf, "check_backpointers_to_extents(): ");
+			bch2_bbpos_to_text(&buf, start);
+			prt_str(&buf, "-");
+			bch2_bbpos_to_text(&buf, end);
+
+			bch_verbose(c, "%s", buf.buf);
+			printbuf_exit(&buf);
+		}
+
+		ret = bch2_check_backpointers_to_extents_pass(&trans, start, end);
+		if (ret || !bbpos_cmp(end, BBPOS_MAX))
+			break;
+
+		start = bbpos_successor(end);
+	}
+	bch2_trans_exit(&trans);
+
+	return ret;
+}

fs/bcachefs/bbpos.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_BBPOS_H
+#define _BCACHEFS_BBPOS_H
+
+#include "bkey_methods.h"
+
+struct bbpos {
+	enum btree_id		btree;
+	struct bpos		pos;
+};
+
+static inline struct bbpos BBPOS(enum btree_id btree, struct bpos pos)
+{
+	return (struct bbpos) { btree, pos };
+}
+
+#define BBPOS_MIN	BBPOS(0, POS_MIN)
+#define BBPOS_MAX	BBPOS(BTREE_ID_NR - 1, POS_MAX)
+
+static inline int bbpos_cmp(struct bbpos l, struct bbpos r)
+{
+	return cmp_int(l.btree, r.btree) ?: bpos_cmp(l.pos, r.pos);
+}
+
+static inline struct bbpos bbpos_successor(struct bbpos pos)
+{
+	if (bpos_cmp(pos.pos, SPOS_MAX)) {
+		pos.pos = bpos_successor(pos.pos);
+		return pos;
+	}
+
+	if (pos.btree != BTREE_ID_NR) {
+		pos.btree++;
+		pos.pos = POS_MIN;
+		return pos;
+	}
+
+	BUG();
+}
+
+static inline void bch2_bbpos_to_text(struct printbuf *out, struct bbpos pos)
+{
+	prt_str(out, bch2_btree_ids[pos.btree]);
+	prt_char(out, ':');
+	bch2_bpos_to_text(out, pos.pos);
+}
+
+#endif /* _BCACHEFS_BBPOS_H */