Re: [PATCH v5 1/2] writeback, cgroup: keep list of inodes attached to bdi_writeback

On Thu, May 27, 2021 at 12:35:17PM +0200, Jan Kara wrote:

On Wed 26-05-21 15:25:56, Roman Gushchin wrote:

quoted

Currently there is no way to iterate over inodes attached to a
specific cgwb structure. It limits the ability to efficiently
reclaim the writeback structure itself and associated memory and
block cgroup structures without scanning all inodes belonging to a sb,
which can be prohibitively expensive.

While dirty/in-active-writeback an inode belongs to one of the
bdi_writeback's io lists: b_dirty, b_io, b_more_io and b_dirty_time.
Once cleaned up, it's removed from all io lists. So the
inode->i_io_list can be reused to maintain the list of inodes,
attached to a bdi_writeback structure.

This patch introduces a new wb->b_attached list, which contains all
inodes which were dirty at least once and are attached to the given
cgwb. Inodes attached to the root bdi_writeback structures are never
placed on such list. The following patch will use this list to try to
release cgwbs structures more efficiently.

Suggested-by: Jan Kara <redacted>
Signed-off-by: Roman Gushchin <redacted>

Looks good. Just some minor nits below:

quoted

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e91980f49388..631ef6366293 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c

@@ -135,18 +135,23 @@ static bool inode_io_list_move_locked(struct inode *inode,
  * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
  * @inode: inode to be removed
  * @wb: bdi_writeback @inode is being removed from
+ * @final: inode is going to be freed and can't reappear on any IO list
  *
  * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
  * clear %WB_has_dirty_io if all are empty afterwards.
  */
 static void inode_io_list_del_locked(struct inode *inode,
-				     struct bdi_writeback *wb)
+				     struct bdi_writeback *wb,
+				     bool final)
 {
 	assert_spin_locked(&wb->list_lock);
 	assert_spin_locked(&inode->i_lock);
 
 	inode->i_state &= ~I_SYNC_QUEUED;
-	list_del_init(&inode->i_io_list);
+	if (final)
+		list_del_init(&inode->i_io_list);
+	else
+		inode_cgwb_move_to_attached(inode, wb);
 	wb_io_lists_depopulated(wb);
 }

With these changes the naming is actually somewhat confusing and the bool
argument makes it even worse. Looking into the code I'd just fold
inode_io_list_del_locked() into inode_io_list_del() and make it really
delete inode from all IO lists. There are currently three other
inode_io_list_del_locked() users:

Yeah, good idea. Will do in the next version. Thanks!