On 2010-12-23 02:19, Fred Isaman wrote:
>
> On Dec 22, 2010, at 5:00 PM, Trond Myklebust wrote:
>
>> On Tue, 2010-12-21 at 23:00 -0500, Fred Isaman wrote:
>>> A lsyout can request return-on-close. How this interacts with the
>>> forgetful model of never sending LAYOUTRETURNS is a bit ambiguous.
>>> We forget any layouts marked roc, and wait for them to be completely
>>> forgotten before continuing with the close. In addition, to compensate
>>> for races with any inflight LAYOUTGETs, and the fact that we do not get
>>> any layout stateid back from the server, we set the barrier to the worst
>>> case scenario of current_seqid + number of outstanding LAYOUTGETS.
>>>
>>> Signed-off-by: Fred Isaman <iisaman@xxxxxxxxxx>
>>> ---
>>> fs/nfs/inode.c | 1 +
>>> fs/nfs/nfs4_fs.h | 2 +-
>>> fs/nfs/nfs4proc.c | 21 +++++++++++-
>>> fs/nfs/nfs4state.c | 7 +++-
>>> fs/nfs/pnfs.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++
>>> fs/nfs/pnfs.h | 28 ++++++++++++++++
>>> include/linux/nfs_fs.h | 1 +
>>> 7 files changed, 138 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
>>> index 43a69da..c64bb40 100644
>>> diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
>>> index 29d504d..90515de 100644
>>> --- a/include/linux/nfs_fs.h
>>> +++ b/include/linux/nfs_fs.h
>>> @@ -190,6 +190,7 @@ struct nfs_inode {
>>> struct rw_semaphore rwsem;
>>>
>>> /* pNFS layout information */
>>> + struct rpc_wait_queue lo_rpcwaitq;
>>> struct pnfs_layout_hdr *layout;
>>> #endif /* CONFIG_NFS_V4*/
>>> #ifdef CONFIG_NFS_FSCACHE
>>
>> I believe that I've asked this before. Why do we need a per-inode
>> rpc_wait_queue just to support pnfs? That's a significant expansion of
>> an already bloated structure.
>>
>> Can we please either make this a single per-filesystem wait queue, or
>> else possibly a pool of wait queues?
>>
>> Trond
>
> This was introduced to avoid deadlocks that were occurring when we had a single wait queue. However, the deadlocks I remember were due to a combination of the fact that, at the time, we handled EAGAIN errors of IO outside the RPC code, and we sent LAYOUTRETURN on such error. Since we do neither now, I believe a single per-filesystem wait queue will suffice. Anyone disagree?
The dead locks were also because we didn't use rpc wait queue but rather a thread based one.
Doing the serialization in the rpc prepare phase using a shared queue should cause dead locks.
Benny
>
> Fred
>
>>
>> --
>> Trond Myklebust
>> Linux NFS client maintainer
>>
>> NetApp
>> Trond.Myklebust@xxxxxxxxxx
>> www.netapp.com
>>
>
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