[PATCH] dquot: do full inode dirty in allocating space

[Shaohua Li]

Alex Shi found a regression when doing ffsb test. The test has several threads,
and each thread creates a small file, write to it and then delete it. ffsb
reports about 20% regression and Alex bisected it to 43d2932d88e4. The test
will call __mark_inode_dirty 3 times. without this commit, we only take
inode_lock one time, while with it, we take the lock 3 times with flags (
I_DIRTY_SYNC,I_DIRTY_PAGES,I_DIRTY). Perf shows the lock contention increased
too much. Below proposed patch fixes it.

fs is allocating blocks, which usually means file writes and the inode
will be dirtied soon. We fully dirty the inode to reduce some inode_lock
contention in several calls of __mark_inode_dirty.

Jan Kara: Added comment.

Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 include/linux/quotaops.h |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
index d50ba85..d1a9193 100644
--- a/include/linux/quotaops.h
+++ b/include/linux/quotaops.h
@@ -274,8 +274,14 @@ static inline int dquot_alloc_space(struct inode *inode, qsize_t nr)
 	int ret;
 
 	ret = dquot_alloc_space_nodirty(inode, nr);
-	if (!ret)
-		mark_inode_dirty_sync(inode);
+	if (!ret) {
+		/*
+		 * Mark inode fully dirty. Since we are allocating blocks, inode
+		 * would become fully dirty soon anyway and it reportedly
+		 * reduces inode_lock contention.
+		 */
+		mark_inode_dirty(inode);
+	}
 	return ret;
 }
 
-- 
1.6.4.2


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