linux-kernel - Re: [PATCH] inode: add hlist_fake to avoid the inode hash lock in evict V2

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Date:	Sat, 14 Mar 2015 08:00:50 +0100
From:	Jan Kara <jack@...e.cz>
To:	Josef Bacik <jbacik@...com>
Cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	david@...morbit.com, jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] inode: add hlist_fake to avoid the inode hash lock in
 evict V2

On Thu 12-03-15 08:20:23, Josef Bacik wrote:
> 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@...com>
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> V1->V2: Argh sorry, forgot to reset the author, my bad.
> 
>  include/linux/fs.h   | 2 +-
>  include/linux/list.h | 5 +++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b4d71b5..31da757 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2528,7 +2528,7 @@ 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);
>  }
>  
> diff --git a/include/linux/list.h b/include/linux/list.h
> index feb773c..3e3e64a 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.
> -- 
> 1.9.3
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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