linux-kernel - [PATCH 2/2] Btrfs: stop caching thread if extetn_commit

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Message-ID: <1379605688-987-2-git-send-email-jbacik@fusionio.com>
Date:	Thu, 19 Sep 2013 11:48:08 -0400
From:	Josef Bacik <jbacik@...ionio.com>
To:	<linux-btrfs@...r.kernel.org>
CC:	<walken@...gle.com>, <linux-kernel@...r.kernel.org>,
	<mingo@...e.hu>, <peter@...leysoftware.com>,
	<akpm@...ux-foundation.org>
Subject: [PATCH 2/2] Btrfs: stop caching thread if extetn_commit_sem is contended

We can starve out the transaction commit with a bunch of caching threads all
running at the same time.  This is because we will only drop the
extent_commit_sem if we need_resched(), which isn't likely to happen since we
will be reading a lot from the disk so have already schedule()'ed plenty.  Alex
observed that he could starve out a transaction commit for up to a minute with
32 caching threads all running at once.  This will allow us to drop the
extent_commit_sem to allow the transaction commit to swap the commit_root out
and then all the cachers will start back up.  Thanks,

Signed-off-by: Josef Bacik <jbacik@...ionio.com>
---
 fs/btrfs/extent-tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index cfb3cf7..cc074c34 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -442,7 +442,8 @@ next:
 			if (ret)
 				break;

-			if (need_resched()) {
+			if (need_resched() ||
+			    rwsem_is_contended(&fs_info->extent_commit_sem)) {
 				caching_ctl->progress = last;
 				btrfs_release_path(path);
 				up_read(&fs_info->extent_commit_sem);
-- 
1.8.3.1

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