inode: add hlist_fake to avoid the inode hash lock in evict

Some filesystems don't use the VFS inode hash and fake the fact they
are hashed so that all the writeback code works correctly. However,
this means the evict() path still tries to remove the inode from the
hash, meaning that the inode_hash_lock() needs to be taken
unnecessarily. Hence under certain workloads the inode_hash_lock can
be contended even if the inode is never actually hashed.

To avoid this add hlist_fake to test if the inode isn't actually
hashed to avoid taking the hash lock on inodes that have never been
hashed.  Based on Dave Chinner's

inode: add IOP_NOTHASHED to avoid inode hash lock in evict

basd on Al's suggestions.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index feb773c76ee0..3e3e64a61002 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -672,6 +672,11 @@ static inline void hlist_add_fake(struct hlist_node *n)
 	n->pprev = &n->next;
 }
 
+static inline bool hlist_fake(struct hlist_node *h)
+{
+	return h->pprev == &h->next;
+}
+
 /*
  * Move a list from one list head to another. Fixup the pprev
  * reference of the first entry if it exists.