Commit cbedaac6 authored Mar 12, 2015 by Josef Bacik

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>

parent d353d758

include/linux/fs.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -2608,7 +2608,7 @@ static inline void insert_inode_hash(struct inode *inode)
		extern void __remove_inode_hash(struct inode *);
		static inline void remove_inode_hash(struct inode *inode)
		{
		if (!inode_unhashed(inode))
		if (!inode_unhashed(inode) && !hlist_fake(&inode->i_hash))
		__remove_inode_hash(inode);
		}

include/linux/list.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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.

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