[PATCH] vfs: conditionally call inode_wb_list_del()

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 27 juillet 2011 à 17:01 -0400, Christoph Hellwig a écrit :
> On Wed, Jul 27, 2011 at 10:59:57PM +0200, Andi Kleen wrote:
> > > 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.
> > 
> > If the caller is in the same file modern gcc is able to do that automatically
> > if you're lucky enough ("partial inlining")
> > 
> > I would not uglify the code for it.
> 
> Depending on how you look at it the code might actually be a tad
> cleaner.  One of called functions is outside of inode.c.
> 

Thats right, thanks again for your valuable input Christoph.

The following is a clear win, since we avoid the call to external
function.

[PATCH] vfs: conditionally call inode_wb_list_del()

Some inodes (pipes, sockets, ...) are not in bdi writeback list.

evict() can avoid calling inode_wb_list_del() and its expensive spinlock
by checking inode i_wb_list being empty or not.

At this point, no other cpu/user can concurrently manipulate this inode
i_wb_list

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 fs/inode.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index d0c72ff..9dab13a 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -454,7 +454,9 @@ static void evict(struct inode *inode)
 	BUG_ON(!(inode->i_state & I_FREEING));
 	BUG_ON(!list_empty(&inode->i_lru));
 
-	inode_wb_list_del(inode);
+	if (!list_empty(&inode->i_wb_list))
+		inode_wb_list_del(inode);
+
 	inode_sb_list_del(inode);
 
 	if (op->evict_inode) {