Re: [PATCH] nfs: Don't return referenced delegations

[Myklebust, Trond]

On Thu, 2012-12-13 at 14:37 +0800, ycnian@xxxxxxxxx wrote:
> From: Yanchuan Nian <ycnian@xxxxxxxxx>
> 
> The client returns unreferenced delegations in state management. It scans all
> delegations and tests the NFS_DELEGATION_REFERENCED flag. if this flag is not
> set, NFS_DELEGATION_RETURN will be set and the delegation will be returned. 
> But unfortunately NFS_DELEGATION_REFERENCED is cleared after the testing, so 
> delegations which are still being used will be returned in the next state
> management.
> 
> Signed-off-by: Yanchuan Nian <ycnian@xxxxxxxxx>
> ---
>  fs/nfs/delegation.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
> index 81c5eec..485e8c0 100644
> --- a/fs/nfs/delegation.c
> +++ b/fs/nfs/delegation.c
> @@ -506,7 +506,7 @@ static void nfs_mark_return_unreferenced_delegations(struct nfs_server *server)
>  	struct nfs_delegation *delegation;
>  
>  	list_for_each_entry_rcu(delegation, &server->delegations, super_list) {
> -		if (test_and_clear_bit(NFS_DELEGATION_REFERENCED, &delegation->flags))
> +		if (test_bit(NFS_DELEGATION_REFERENCED, &delegation->flags))
>  			continue;
>  		nfs_mark_return_delegation(server, delegation);
>  	}

The clearing of the bit here is 100% intentional. This is a variant on
basic mark-and-sweep garbage collection where if the bit hasn't been set
again the next time we scan, then we assume the delegation isn't being
used.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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