We track two conditions to decide if we should sleep while waiting for more
delayed refs, the number of delayed refs (num_refs) and the first entry in
the list of blockers (first_seq).
When we suspect staleness, we save num_refs and do one more cycle. If
nothing changes, we then save first_seq for later comparison and do
wait_event. We ought to save first_seq the very same moment we're saving
num_refs. Otherwise we cannot be sure that nothing has changed and we might
start waiting when we shouldn't, which could lead to starvation.
Signed-off-by: Jan Schmidt <list.btrfs@xxxxxxxxxxxxx>
---
fs/btrfs/extent-tree.c | 11 ++++++-----
1 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4b5a1e1..6e1d367 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2347,12 +2347,10 @@ next:
return count;
}
-
static void wait_for_more_refs(struct btrfs_delayed_ref_root *delayed_refs,
- unsigned long num_refs)
+ unsigned long num_refs,
+ struct list_head *first_seq)
{
- struct list_head *first_seq = delayed_refs->seq_head.next;
-
spin_unlock(&delayed_refs->lock);
pr_debug("waiting for more refs (num %ld, first %p)\n",
num_refs, first_seq);
@@ -2381,6 +2379,7 @@ int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
struct btrfs_delayed_ref_root *delayed_refs;
struct btrfs_delayed_ref_node *ref;
struct list_head cluster;
+ struct list_head *first_seq = NULL;
int ret;
u64 delayed_start;
int run_all = count == (unsigned long)-1;
@@ -2436,8 +2435,10 @@ again:
*/
consider_waiting = 1;
num_refs = delayed_refs->num_entries;
+ first_seq = root->fs_info->tree_mod_seq_list.next;
} else {
- wait_for_more_refs(delayed_refs, num_refs);
+ wait_for_more_refs(delayed_refs,
+ num_refs, first_seq);
/*
* after waiting, things have changed. we
* dropped the lock and someone else might have
--
1.7.3.4
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
