From: Kent Overstreet <kent.overstreet@linux.dev>
Date: Sun, 17 Nov 2024 19:39:46 +0000 (-0500)
Subject: bcachefs: btree_and_journal_iter: don't iterate over too many whiteouts when prefetching
X-Git-Tag: v6.14-rc1~204^2~169
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=854724d116cbd1145cd3888239a5cc7ea44d8cdc;p=thirdparty%2Flinux.git

bcachefs: btree_and_journal_iter: don't iterate over too many whiteouts when prefetching

To help ameloriate issues with peek operations having to skip over
deletions in the journal - just bail out if all we're doing is
prefetching btree nodes.

Since btree node prefetching runs every time we iterate to a new node,
and has to sequentially scan ahead, this avoids another O(n^2).

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

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index ed74f0655d984..89f9665ce70d9 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -825,6 +825,8 @@ static int btree_path_prefetch_j(struct btree_trans *trans, struct btree_path *p
 
 	bch2_bkey_buf_init(&tmp);
 
+	jiter->fail_if_too_many_whiteouts = true;
+
 	while (nr-- && !ret) {
 		if (!bch2_btree_node_relock(trans, path, path->level))
 			break;
diff --git a/fs/bcachefs/btree_journal_iter.c b/fs/bcachefs/btree_journal_iter.c
index dbc9bc233ccae..cc7f5fad90c6d 100644
--- a/fs/bcachefs/btree_journal_iter.c
+++ b/fs/bcachefs/btree_journal_iter.c
@@ -426,6 +426,7 @@ static void btree_and_journal_iter_prefetch(struct btree_and_journal_iter *_iter
 		: (level > 1 ? 1 : 16);
 
 	iter.prefetch = false;
+	iter.fail_if_too_many_whiteouts = true;
 	bch2_bkey_buf_init(&tmp);
 
 	while (nr--) {
@@ -444,6 +445,7 @@ static void btree_and_journal_iter_prefetch(struct btree_and_journal_iter *_iter
 struct bkey_s_c bch2_btree_and_journal_iter_peek(struct btree_and_journal_iter *iter)
 {
 	struct bkey_s_c btree_k, journal_k = bkey_s_c_null, ret;
+	size_t iters = 0;
 
 	if (iter->prefetch && iter->journal.level)
 		btree_and_journal_iter_prefetch(iter);
@@ -451,6 +453,11 @@ again:
 	if (iter->at_end)
 		return bkey_s_c_null;
 
+	iters++;
+
+	if (iters > 20 && iter->fail_if_too_many_whiteouts)
+		return bkey_s_c_null;
+
 	while ((btree_k = bch2_journal_iter_peek_btree(iter)).k &&
 	       bpos_lt(btree_k.k->p, iter->pos))
 		bch2_journal_iter_advance_btree(iter);
diff --git a/fs/bcachefs/btree_journal_iter.h b/fs/bcachefs/btree_journal_iter.h
index 118ada4cdd1b1..9e8f8ab1c6ffe 100644
--- a/fs/bcachefs/btree_journal_iter.h
+++ b/fs/bcachefs/btree_journal_iter.h
@@ -26,6 +26,7 @@ struct btree_and_journal_iter {
 	struct bpos		pos;
 	bool			at_end;
 	bool			prefetch;
+	bool			fail_if_too_many_whiteouts;
 };
 
 static inline int __journal_key_btree_cmp(enum btree_id	l_btree_id,