[PATCH 15/19] btrfs: load block_groups into discard_list on mount

[Dennis Zhou <dennis@kernel.org>]

Async discard doesn't remember the discard state of a block_group when
unmounting or when we crash. So, any block_group that is not fully used
may have undiscarded regions. However, free space caches are read in on
demand. Let the discard worker read in the free space cache so we can
proceed with discarding rather than wait for the block_group to be used.
This prevents us from indefinitely deferring discards until that
particular block_group is reused.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
---
 fs/btrfs/block-group.c |  2 ++
 fs/btrfs/discard.c     | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 73e5a9384491..684959c96c3f 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1859,6 +1859,8 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
 						&info->discard_ctl, cache);
 			else
 				btrfs_mark_bg_unused(cache);
+		} else if (btrfs_test_opt(info, DISCARD_ASYNC)) {
+			btrfs_add_to_discard_list(&info->discard_ctl, cache);
 		}
 	}
 
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 0e4d5a22c661..d99ba31e6f3b 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -246,6 +246,7 @@ static void btrfs_discard_workfn(struct work_struct *work)
 	int discard_index = 0;
 	u64 trimmed = 0;
 	u64 minlen = 0;
+	int ret;
 
 	discard_ctl = container_of(work, struct btrfs_discard_ctl, work.work);
 
@@ -254,6 +255,19 @@ static void btrfs_discard_workfn(struct work_struct *work)
 	if (!cache || !btrfs_run_discard_work(discard_ctl))
 		return;
 
+	if (!btrfs_block_group_cache_done(cache)) {
+		ret = btrfs_cache_block_group(cache, 0);
+		if (ret) {
+			remove_from_discard_list(discard_ctl, cache);
+			goto out;
+		}
+		ret = btrfs_wait_block_group_cache_done(cache);
+		if (ret) {
+			remove_from_discard_list(discard_ctl, cache);
+			goto out;
+		}
+	}
+
 	minlen = discard_minlen[discard_index];
 
 	if (btrfs_discard_bitmaps(cache)) {
@@ -291,6 +305,7 @@ static void btrfs_discard_workfn(struct work_struct *work)
 		}
 	}
 
+out:
 	spin_lock(&discard_ctl->lock);
 	discard_ctl->cache = NULL;
 	spin_unlock(&discard_ctl->lock);
-- 
2.17.1