linux-kernel - Re: [PATCH] vfs: avoid taking locks if inode not in lists

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Date:	Thu, 28 Jul 2011 06:41:09 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	David Miller <davem@...emloft.net>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Anton Blanchard <anton@...ba.org>, npiggin@...nel.dk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] vfs: avoid taking locks if inode not in lists

Le mercredi 27 juillet 2011 à 16:44 -0400, Christoph Hellwig a écrit :
> On Wed, Jul 27, 2011 at 05:21:05PM +0200, Eric Dumazet wrote:
> > If I am not mistaken, we can add unlocked checks on the three hot spots.
> > 
> > After following patch, a close(socket(PF_INET, SOCK_DGRAM, 0)) pair on
> > my dev machine takes ~3us instead of ~9us.
> > 
> > Maybe its better to split it in three patches, just let me know.
> 
> I think three patches would be a lot cleaner.
> 
> As for safety of the unlocked checks:
> 
>  - inode are either hashed when created or never, so that one looks
>    fine.
>  - same for the sb list.
>  - the writeback list is a bit more dynamic as we move things around
>    quite a bit.  But in additon to the inode_wb_list_del call from
>    evict() it only ever gets remove in writeback_single_inode, which
>    for a freeing inode can only be called from the callers of evict().
> 
> Btw, I wonder if you should micro-optimize things a bit further by
> moving the unhashed checks from the deletion functions into the callers
> and thus save a function call for each of them.
> 

What about following patch, addressing the micro-optimization and Andi
Kleen concern about evict() readability ?

Thanks !

[PATCH] vfs: avoid taking inode_hash_lock on pipes and sockets

Some inodes (pipes, sockets, ...) are not hashed, no need to take
contended inode_hash_lock at dismantle time.

nice speedup on SMP machines on socket intensive workloads.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 fs/inode.c         |    6 +++---
 include/linux/fs.h |    9 ++++++++-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index d0c72ff..73b5598 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -399,12 +399,12 @@ void __insert_inode_hash(struct inode *inode, unsigned long hashval)
 EXPORT_SYMBOL(__insert_inode_hash);
 
 /**
- *	remove_inode_hash - remove an inode from the hash
+ *	__remove_inode_hash - remove an inode from the hash
  *	@inode: inode to unhash
  *
  *	Remove an inode from the superblock.
  */
-void remove_inode_hash(struct inode *inode)
+void __remove_inode_hash(struct inode *inode)
 {
 	spin_lock(&inode_hash_lock);
 	spin_lock(&inode->i_lock);
@@ -412,7 +412,7 @@ void remove_inode_hash(struct inode *inode)
 	spin_unlock(&inode->i_lock);
 	spin_unlock(&inode_hash_lock);
 }
-EXPORT_SYMBOL(remove_inode_hash);
+EXPORT_SYMBOL(__remove_inode_hash);
 
 void end_writeback(struct inode *inode)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f23bcb7..786b3b1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2317,11 +2317,18 @@ extern int should_remove_suid(struct dentry *);
 extern int file_remove_suid(struct file *);
 
 extern void __insert_inode_hash(struct inode *, unsigned long hashval);
-extern void remove_inode_hash(struct inode *);
 static inline void insert_inode_hash(struct inode *inode)
 {
 	__insert_inode_hash(inode, inode->i_ino);
 }
+
+extern void __remove_inode_hash(struct inode *);
+static inline void remove_inode_hash(struct inode *inode)
+{
+	if (!inode_unhashed(inode))
+		__remove_inode_hash(inode);
+}
+
 extern void inode_sb_list_add(struct inode *inode);
 
 #ifdef CONFIG_BLOCK


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