Btrfs: adjust the write_lock_level as we unlock
btrfs_search_slot sometimes needs write locks on high levels of
the tree. It remembers the highest level that needs a write lock
and will use that for all future searches through the tree in a given
call.
But, very often we'll just cow the top level or the level below and we
won't really need write locks on the root again after that. This patch
changes things to adjust the write lock requirement as it unlocks
levels.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 8af24da..270655d 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1395,7 +1395,8 @@
* if lowest_unlock is 1, level 0 won't be unlocked
*/
static noinline void unlock_up(struct btrfs_path *path, int level,
- int lowest_unlock)
+ int lowest_unlock, int min_write_lock_level,
+ int *write_lock_level)
{
int i;
int skip_level = level;
@@ -1427,6 +1428,11 @@
if (i >= lowest_unlock && i > skip_level && path->locks[i]) {
btrfs_tree_unlock_rw(t, path->locks[i]);
path->locks[i] = 0;
+ if (write_lock_level &&
+ i > min_write_lock_level &&
+ i <= *write_lock_level) {
+ *write_lock_level = i - 1;
+ }
}
}
}
@@ -1650,6 +1656,7 @@
/* everything at write_lock_level or lower must be write locked */
int write_lock_level = 0;
u8 lowest_level = 0;
+ int min_write_lock_level;
lowest_level = p->lowest_level;
WARN_ON(lowest_level && ins_len > 0);
@@ -1677,6 +1684,8 @@
if (cow && (p->keep_locks || p->lowest_level))
write_lock_level = BTRFS_MAX_LEVEL;
+ min_write_lock_level = write_lock_level;
+
again:
/*
* we try very hard to do read locks on the root
@@ -1808,7 +1817,8 @@
goto again;
}
- unlock_up(p, level, lowest_unlock);
+ unlock_up(p, level, lowest_unlock,
+ min_write_lock_level, &write_lock_level);
if (level == lowest_level) {
if (dec)
@@ -1870,7 +1880,8 @@
}
}
if (!p->search_for_split)
- unlock_up(p, level, lowest_unlock);
+ unlock_up(p, level, lowest_unlock,
+ min_write_lock_level, &write_lock_level);
goto done;
}
}
@@ -4108,7 +4119,7 @@
path->slots[level] = slot;
if (level == path->lowest_level) {
ret = 0;
- unlock_up(path, level, 1);
+ unlock_up(path, level, 1, 0, NULL);
goto out;
}
btrfs_set_path_blocking(path);
@@ -4119,7 +4130,7 @@
path->locks[level - 1] = BTRFS_READ_LOCK;
path->nodes[level - 1] = cur;
- unlock_up(path, level, 1);
+ unlock_up(path, level, 1, 0, NULL);
btrfs_clear_path_blocking(path, NULL, 0);
}
out:
@@ -4355,7 +4366,7 @@
}
ret = 0;
done:
- unlock_up(path, 0, 1);
+ unlock_up(path, 0, 1, 0, NULL);
path->leave_spinning = old_spinning;
if (!old_spinning)
btrfs_set_path_blocking(path);