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bcachefs: Improve btree_node_mem_ptr optimization

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This patch checks b->hash_val before attempting to lock the node in the
btree, which makes it more equivalent to the "lookup in hash table"
path - and potentially avoids an unnecessary transaction restart if
btree_node_mem_ptr(k) no longer points to the node we want.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
This commit is contained in:
Kent Overstreet 2021-09-13 16:04:49 -04:00 committed by Kent Overstreet
parent aa76bd3321
commit aae4eea60c
1 changed files with 6 additions and 1 deletions
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7
fs/bcachefs/btree_cache.c
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@ -777,7 +777,12 @@ struct btree *bch2_btree_node_get(struct btree_trans *trans, struct btree_path *
if (c->opts.btree_node_mem_ptr_optimization) {
b = btree_node_mem_ptr(k);
if (b)
/*
* Check b->hash_val _before_ calling btree_node_lock() - this
* might not be the node we want anymore, and trying to lock the
* wrong node could cause an unneccessary transaction restart:
*/
if (b && b->hash_val == btree_ptr_hash_val(k))
goto lock_node;
}
retry: