From: Jeff Layton <jeff.layton@primarydata.com>
Date: Thu, 19 Jun 2014 11:33:28 -0400
To: bfields@fieldses.org
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH v1 000/104] nfsd: eliminate the client_mutex
Message-ID: <20140619113328.598cf759@tlielax.poochiereds.net>
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References: <1403189450-18729-1-git-send-email-jlayton@primarydata.com>
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On Thu, 19 Jun 2014 10:49:06 -0400
Jeff Layton <jlayton@primarydata.com> wrote:

> Here it is. The long awaited removal of the client_mutex from knfsd.
> As many of us are aware, one of the major bottlenecks in NFSv4 serving
> is the fact that all compounds are processed while holding a single,
> global mutex.
> 
> This has an obvious detrimental effect on scalability. I've heard
> anecdotal reports of 10x slowdowns with v4 serving vs. v3 on the same
> machine, primarily due to it.
> 
> This patchset eliminates that mutex and (hopefully!) the bottleneck
> that it imposes. The basic idea is to add refcounting to most of the
> objects that compounds deal with to ensure that they are pinned while
> in use. Spinlocks are used to protect things like the hashtables and
> trees that track the objects.
> 
> Benny started this set quite some time ago, and Trond took up the
> torch early this spring. He then handed it to me to clean up the
> remaining bits about a month ago.
> 
> I'd like to see this considered for v3.17. Obviously, getting it into
> linux-next ASAP would be a good thing once it passes review.
> 
> Some other highlights/notes:
> 
> - use of lockdep has been greatly increased. I found it was the only
>   way to ensure that I didn't create lock inversion problems and such.
> 
> - clients are now only looked up once per compund and are cached in
>   the cstate. This keeps us from having to keep searching for the
>   same client for each compound op.
> 
> - openowners and lockowners are now handled more sanely. References
>   to them are only held by the stateids that are associated with them,
>   and they are destroyed when the last reference to them is put. Also,
>   lockowners can now have more than one stateid (in accordance with
>   the spec)
> 
> - the fault injection code has been overhauled. It should look the same
>   to users, but it needed major work to deal with the new locking.
>   It's probably possible to consolidate some of that code as well --
>   it more cut-and-pastey than I'd like.
> 
> - I've added a file to document how all of the moving parts fit
>   together. It probably can use more fleshing out, but it's a start.
> 
> - the lease handling is now a bit more complex than I'd like. Lease
>   removal in particular is currently called under a spinlock, which
>   I think we'll need to eventually clean up. For now, this is ok
>   since the first thing that vfs_setlease does is lock the i_lock,
>   but I think we'll eventually need to do an i_lock pushdown in the
>   lease handling code, and ensure that vfs_setlease isn't called
>   under a spinlock.
> 
> As always, comments and review are welcome.
> 
> Benny Halevy (1):
>   nfsd4: use cl_lock to synchronize all stateid idr calls
> 
> Jeff Layton (40):
>   NFSd: Ensure that nfs4_file_get_access enforces share access modes
>   locks: add file_has_lease
>   NFSd: Protect the nfs4_file delegation fields using the fi_lock
>   NFSd: Allow lockowners to hold several stateids
>   NFSd: Ensure atomicity of stateid destruction and idr tree removal
>   NFSd: Cleanup the freeing of stateids
>   nfsd: do filp_close in sc_free callback for lock stateids
>   NFSd: Add locking to protect the state owner lists
>   nfsd: clean up races in lock stateid searching and creation
>   nfsd: clean up lockowner refcounting when finding them
>   nfsd: add an operation for unhashing a stateowner
>   nfsd: clean up nfs4_release_lockowner
>   nfsd: clean up refcounting for lockowners
>   nfsd: declare v4.1+ openowners confirmed on creation
>   nfsd: make openstateids hold references to their openowners
>   nfsd: don't allow CLOSE to proceed until refcount on stateid drops
>   lockdep: add lockdep_assert_not_held
>   nfsd: add locking to stateowner release
>   nfsd: optimize destroy_lockowner cl_lock thrashing
>   nfsd: reduce cl_lock trashing in release_openowner
>   NFSd: Protect session creation and client confirm using client_lock
>   nfsd: protect the close_lru list and oo_last_closed_stid with
>     client_lock
>   nfsd: ensure that clp->cl_revoked list is protected by clp->cl_lock
>   nfsd: move unhash_client_locked call into mark_client_expired_locked
>   nfsd: fix misleading comment
>   nfsd: don't destroy client if mark_client_expired_locked fails
>   nfsd: don't destroy clients that are busy
>   nfsd: abstract out the get and set routines into the fault injection
>     ops
>   nfsd: add a forget_clients "get" routine with proper locking
>   nfsd: add a forget_client set_clnt routine
>   nfsd: add nfsd_inject_forget_clients
>   nfsd: add a list_head arg to nfsd_foreach_client_lock
>   nfsd: add more granular locking to forget_locks fault injector
>   nfsd: add more granular locking to forget_openowners fault injector
>   nfsd: add more granular locking to *_delegations fault injectors
>   nfsd: remove old fault injection infrastructure
>   nfsd: remove nfs4_lock_state: nfs4_laundromat
>   nfsd: remove nfs4_lock_state: nfs4_state_shutdown_net
>   nfsd: remove the client_mutex and the nfs4_lock/unlock_state wrappers
>   nfsd: add file documenting new state object model
> 
> Trond Myklebust (63):
>   nfsd: Protect addition to the file_hashtbl
>   NFSd: Avoid taking state_lock while holding inode lock in
>     nfsd_break_one_deleg
>   NFSd: nfs4_preprocess_seqid_op should only set *stpp on success
>   NFSd: Add fine grained protection for the nfs4_file->fi_stateids list
>   NFSd: Add a mutex to protect the NFSv4.0 open owner replay cache
>   NFSd: Add locking to the nfs4_file->fi_fds[] array
>   NFSd: Lock owners are not per open stateid
>   NFSd: Clean up helper __release_lock_stateid
>   NFSd: NFSv4 lock-owners are not associated to a specific file
>   NFSd: Cleanup nfs4svc_encode_compoundres
>   NFSd: Don't get a session reference without a client reference
>   NFSd: Allow struct nfsd4_compound_state to cache the nfs4_client
>   NFSd: Move the delegation reference counter into the struct nfs4_stid
>   NFSd: Simplify stateid management
>   NFSd: Fix delegation revocation
>   NFSd: Add reference counting to the lock and open stateids
>   NFSd: clean up nfsd4_close_open_stateid
>   NFSd: Add a struct nfs4_file field to struct nfs4_stid
>   NFSd: Replace nfs4_ol_stateid->st_file with the st_stid.sc_file
>   NFSd: Ensure stateids remain unique until they are freed
>   NFSd: Convert delegation counter to an atomic_long_t type
>   NFSd: Slight cleanup of find_stateid()
>   NFSd: Add reference counting to find_stateid
>   NFSd: Add reference counting to lock stateids
>   NFSd: nfsd4_locku() must reference the lock stateid
>   NFSd: Ensure that nfs4_open_delegation() references the delegation
>     stateid
>   NFSd: nfsd4_process_open2() must reference the delegation stateid
>   NFSd: nfsd4_process_open2() must reference the open stateid
>   NFSd: Prepare nfsd4_close() for open stateid referencing
>   NFSd: nfsd4_open_confirm() must reference the open stateid
>   NFSd: Add reference counting to nfs4_preprocess_confirmed_seqid_op
>   NFSd: Migrate the stateid reference into nfs4_preprocess_seqid_op
>   NFSd: Migrate the stateid reference into nfs4_lookup_stateid()
>   NFSd: Migrate the stateid reference into nfs4_find_stateid_by_type()
>   NFSd: Add reference counting to state owners
>   NFSd: Keep a reference to the open stateid for the NFSv4.0 replay
>     cache
>   NFSd: Make lock stateid take a reference to the lockowner
>   NFSd: Protect adding/removing open state owners using client_lock
>   NFSd: Protect adding/removing lock owners using client_lock
>   NFSd: Cleanup - Let nfsd4_lookup_stateid() take a cstate argument
>   NFSd: Cache the client that was looked up in lookup_clientid()
>   NFSd: Convert nfsd4_process_open1() to work with lookup_clientid()
>   NFSd: Always use lookup_clientid() in nfsd4_process_open1
>   NFSd: Move the open owner hash table into struct nfs4_client
>   NFSd: Convert nfs4_check_open_reclaim() to work with lookup_clientid()
>   NFSd: Ensure struct nfs4_client is unhashed before we try to destroy
>     it
>   NFSd: Ensure that the laundromat unhashes the client before releasing
>     locks
>   NFSd: Don't require client_lock in free_client
>   NFSd: Move create_client() call outside the lock
>   NFSd: Protect unconfirmed client creation using client_lock
>   NFSd: Protect nfsd4_destroy_clientid using client_lock
>   NFSd: Ensure lookup_clientid() takes client_lock
>   NFSd: Add assertions to document the nfs4_client/session locking
>   NFSd: Remove nfs4_lock_state(): nfs4_preprocess_stateid_op()
>   NFSd: Remove nfs4_lock_state(): nfsd4_test_stateid/nfsd4_free_stateid
>   NFSd: Remove nfs4_lock_state(): nfsd4_release_lockowner
>   NFSd: Remove nfs4_lock_state(): nfsd4_lock/locku/lockt()
>   NFSd: Remove nfs4_lock_state(): nfsd4_open_downgrade + nfsd4_close
>   NFSd: Remove nfs4_lock_state(): nfsd4_delegreturn()
>   NFSd: Remove nfs4_lock_state(): nfsd4_open and nfsd4_open_confirm
>   NFSd: Remove nfs4_lock_state(): exchange_id, create/destroy_session()
>   NFSd: Remove nfs4_lock_state(): setclientid, setclientid_confirm,
>     renew
>   NFSd: Remove nfs4_lock_state(): reclaim_complete()
> 
>  .../filesystems/nfs/nfsd4-state-objects.txt        |  110 +
>  fs/locks.c                                         |   26 +
>  fs/nfsd/fault_inject.c                             |  129 +-
>  fs/nfsd/netns.h                                    |    5 -
>  fs/nfsd/nfs4callback.c                             |   18 +-
>  fs/nfsd/nfs4proc.c                                 |   16 +-
>  fs/nfsd/nfs4state.c                                | 2569 ++++++++++++++------
>  fs/nfsd/nfs4xdr.c                                  |   17 +-
>  fs/nfsd/state.h                                    |   86 +-
>  fs/nfsd/xdr4.h                                     |    8 +-
>  include/linux/fs.h                                 |    6 +
>  include/linux/lockdep.h                            |    6 +
>  12 files changed, 2052 insertions(+), 944 deletions(-)
>  create mode 100644 Documentation/filesystems/nfs/nfsd4-state-objects.txt
> 

Oh, I should also mention that this set is also available in my
nfsd-devel branch at:

    git://git.samba.org/jlayton/linux.git

I'll continue to push changes to the set to that branch as review comes
in.

Thanks!
-- 
Jeff Layton <jlayton@primarydata.com>