btrfs: rework wake_all_tickets

Now that we no longer partially fill tickets we need to rework
wake_all_tickets to call btrfs_try_to_wakeup_tickets() in order to see
if any subsequent tickets are able to be satisfied.  If our tickets_id
changes we know something happened and we can keep flushing.

Also if we find a ticket that is smaller than the first ticket in our
queue then we want to retry the flushing loop again in case
may_commit_transaction() decides we could satisfy the ticket by
committing the transaction.

Rename this to maybe_fail_all_tickets() while we're at it, to better
reflect what the function is actually doing.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index fe3d7e3..eb4a926 100644 (file)
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -679,19 +679,61 @@ static inline int need_do_async_reclaim(struct btrfs_fs_info *fs_info,
                !test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
 }
 
-static bool wake_all_tickets(struct list_head *head)
+/*
+ * maybe_fail_all_tickets - we've exhausted our flushing, start failing tickets
+ * @fs_info - fs_info for this fs
+ * @space_info - the space info we were flushing
+ *
+ * We call this when we've exhausted our flushing ability and haven't made
+ * progress in satisfying tickets.  The reservation code handles tickets in
+ * order, so if there is a large ticket first and then smaller ones we could
+ * very well satisfy the smaller tickets.  This will attempt to wake up any
+ * tickets in the list to catch this case.
+ *
+ * This function returns true if it was able to make progress by clearing out
+ * other tickets, or if it stumbles across a ticket that was smaller than the
+ * first ticket.
+ */
+static bool maybe_fail_all_tickets(struct btrfs_fs_info *fs_info,
+                                  struct btrfs_space_info *space_info)
 {
        struct reserve_ticket *ticket;
+       u64 tickets_id = space_info->tickets_id;
+       u64 first_ticket_bytes = 0;
+
+       while (!list_empty(&space_info->tickets) &&
+              tickets_id == space_info->tickets_id) {
+               ticket = list_first_entry(&space_info->tickets,
+                                         struct reserve_ticket, list);
+
+               /*
+                * may_commit_transaction will avoid committing the transaction
+                * if it doesn't feel like the space reclaimed by the commit
+                * would result in the ticket succeeding.  However if we have a
+                * smaller ticket in the queue it may be small enough to be
+                * satisified by committing the transaction, so if any
+                * subsequent ticket is smaller than the first ticket go ahead
+                * and send us back for another loop through the enospc flushing
+                * code.
+                */
+               if (first_ticket_bytes == 0)
+                       first_ticket_bytes = ticket->bytes;
+               else if (first_ticket_bytes > ticket->bytes)
+                       return true;
 
-       while (!list_empty(head)) {
-               ticket = list_first_entry(head, struct reserve_ticket, list);
                list_del_init(&ticket->list);
                ticket->error = -ENOSPC;
                wake_up(&ticket->wait);
-               if (ticket->bytes != ticket->orig_bytes)
-                       return true;
+
+               /*
+                * We're just throwing tickets away, so more flushing may not
+                * trip over btrfs_try_granting_tickets, so we need to call it
+                * here to see if we can make progress with the next ticket in
+                * the list.
+                */
+               btrfs_try_granting_tickets(fs_info, space_info);
        }
-       return false;
+       return (tickets_id != space_info->tickets_id);
 }
 
 /*
@@ -759,7 +801,7 @@ static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
                if (flush_state > COMMIT_TRANS) {
                        commit_cycles++;
                        if (commit_cycles > 2) {
-                               if (wake_all_tickets(&space_info->tickets)) {
+                               if (maybe_fail_all_tickets(fs_info, space_info)) {
                                        flush_state = FLUSH_DELAYED_ITEMS_NR;
                                        commit_cycles--;
                                } else {