From f36f3042eae238bdaefe7c79310afe573bfc3622 Mon Sep 17 00:00:00 2001
From: Chris Mason <chris.mason@oracle.com>
Date: Thu, 30 Jul 2009 10:04:48 -0400
Subject: [PATCH] Btrfs: be more polite in the async caching threads

The semaphore used by the async caching threads can prevent a
transaction commit, which can make the FS appear to stall.  This
releases the semaphore more often when a transaction commit is
in progress.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
---
 fs/btrfs/extent-tree.c |  5 +++--
 fs/btrfs/transaction.c | 10 ++++++++++
 fs/btrfs/transaction.h |  1 +
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2fe21fa74913..dc84daee6bc4 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -302,10 +302,11 @@ static int caching_kthread(void *data)
 			else if (ret)
 				break;
 
-			if (need_resched()) {
+			if (need_resched() ||
+			    btrfs_transaction_in_commit(fs_info)) {
 				btrfs_release_path(fs_info->extent_root, path);
 				up_read(&fs_info->extent_commit_sem);
-				cond_resched();
+				schedule_timeout(1);
 				goto again;
 			}
 
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index de48e4ec808c..cdbb5022da52 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -857,6 +857,16 @@ static void update_super_roots(struct btrfs_root *root)
 	super->root_level = root_item->level;
 }
 
+int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
+{
+	int ret = 0;
+	spin_lock(&info->new_trans_lock);
+	if (info->running_transaction)
+		ret = info->running_transaction->in_commit;
+	spin_unlock(&info->new_trans_lock);
+	return ret;
+}
+
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 961c3ee5a2e1..663c67404918 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -107,4 +107,5 @@ int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
 				struct btrfs_root *root);
 int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
 					struct extent_io_tree *dirty_pages);
+int btrfs_transaction_in_commit(struct btrfs_fs_info *info);
 #endif