Btrfs: introduce free_extent_buffer_stale
Because btrfs cow's we can end up with extent buffers that are no longer
necessary just sitting around in memory. So instead of evicting these pages, we
could end up evicting things we actually care about. Thus we have
free_extent_buffer_stale for use when we are freeing tree blocks. This will
make it so that the ref for the eb being in the radix tree is dropped as soon as
possible and then is freed when the refcount hits 0 instead of waiting to be
released by releasepage. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0639a55..74c03fb 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -156,10 +156,23 @@
{
struct extent_buffer *eb;
- rcu_read_lock();
- eb = rcu_dereference(root->node);
- extent_buffer_get(eb);
- rcu_read_unlock();
+ while (1) {
+ rcu_read_lock();
+ eb = rcu_dereference(root->node);
+
+ /*
+ * RCU really hurts here, we could free up the root node because
+ * it was cow'ed but we may not get the new root node yet so do
+ * the inc_not_zero dance and if it doesn't work then
+ * synchronize_rcu and try again.
+ */
+ if (atomic_inc_not_zero(&eb->refs)) {
+ rcu_read_unlock();
+ break;
+ }
+ rcu_read_unlock();
+ synchronize_rcu();
+ }
return eb;
}
@@ -504,7 +517,7 @@
}
if (unlock_orig)
btrfs_tree_unlock(buf);
- free_extent_buffer(buf);
+ free_extent_buffer_stale(buf);
btrfs_mark_buffer_dirty(cow);
*cow_ret = cow;
return 0;
@@ -959,7 +972,7 @@
root_sub_used(root, mid->len);
btrfs_free_tree_block(trans, root, mid, 0, 1, 0);
/* once for the root ptr */
- free_extent_buffer(mid);
+ free_extent_buffer_stale(mid);
return 0;
}
if (btrfs_header_nritems(mid) >
@@ -1016,7 +1029,7 @@
ret = wret;
root_sub_used(root, right->len);
btrfs_free_tree_block(trans, root, right, 0, 1, 0);
- free_extent_buffer(right);
+ free_extent_buffer_stale(right);
right = NULL;
} else {
struct btrfs_disk_key right_key;
@@ -1056,7 +1069,7 @@
ret = wret;
root_sub_used(root, mid->len);
btrfs_free_tree_block(trans, root, mid, 0, 1, 0);
- free_extent_buffer(mid);
+ free_extent_buffer_stale(mid);
mid = NULL;
} else {
/* update the parent key to reflect our changes */
@@ -3781,7 +3794,9 @@
root_sub_used(root, leaf->len);
+ extent_buffer_get(leaf);
btrfs_free_tree_block(trans, root, leaf, 0, 1, 0);
+ free_extent_buffer_stale(leaf);
return 0;
}
/*