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Message-ID: <20130613150247.GB20666@fieldses.org>
Date: Thu, 13 Jun 2013 11:02:47 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: Jeff Layton <jlayton@...hat.com>
Cc: viro@...iv.linux.org.uk, matthew@....cx, dhowells@...hat.com,
sage@...tank.com, smfrench@...il.com, swhiteho@...hat.com,
Trond.Myklebust@...app.com, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, linux-afs@...ts.infradead.org,
ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
samba-technical@...ts.samba.org, cluster-devel@...hat.com,
linux-nfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
piastryyy@...il.com
Subject: Re: [PATCH v2 12/14] locks: give the blocked_hash its own spinlock
On Tue, Jun 11, 2013 at 07:09:06AM -0400, Jeff Layton wrote:
> There's no reason we have to protect the blocked_hash and file_lock_list
> with the same spinlock. With the tests I have, breaking it in two gives
> a barely measurable performance benefit, but it seems reasonable to make
> this locking as granular as possible.
Out of curiosity... In the typical case when adding/removing a lock,
aren't both lists being modified in rapid succession?
I wonder if it would be better to instead stick with one lock and take
care to acquire it only once to cover both manipulations.
--b.
>
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> ---
> Documentation/filesystems/Locking | 16 ++++++++--------
> fs/locks.c | 25 +++++++++++++------------
> 2 files changed, 21 insertions(+), 20 deletions(-)
>
> diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
> index ee351ac..8d8d040 100644
> --- a/Documentation/filesystems/Locking
> +++ b/Documentation/filesystems/Locking
> @@ -359,20 +359,20 @@ prototypes:
>
> locking rules:
>
> - inode->i_lock file_lock_lock may block
> -lm_compare_owner: yes maybe no
> -lm_owner_key yes yes no
> -lm_notify: yes no no
> -lm_grant: no no no
> -lm_break: yes no no
> -lm_change yes no no
> + inode->i_lock blocked_hash_lock may block
> +lm_compare_owner: yes maybe no
> +lm_owner_key yes yes no
> +lm_notify: yes no no
> +lm_grant: no no no
> +lm_break: yes no no
> +lm_change yes no no
>
> ->lm_compare_owner and ->lm_owner_key are generally called with
> *an* inode->i_lock held. It may not be the i_lock of the inode
> associated with either file_lock argument! This is the case with deadlock
> detection, since the code has to chase down the owners of locks that may
> be entirely unrelated to the one on which the lock is being acquired.
> -For deadlock detection however, the file_lock_lock is also held. The
> +For deadlock detection however, the blocked_hash_lock is also held. The
> fact that these locks are held ensures that the file_locks do not
> disappear out from under you while doing the comparison or generating an
> owner key.
> diff --git a/fs/locks.c b/fs/locks.c
> index 11e7784..8124fc1 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -162,12 +162,11 @@ int lease_break_time = 45;
> */
> #define BLOCKED_HASH_BITS 7
>
> +static DEFINE_SPINLOCK(blocked_hash_lock);
> static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);
>
> -static HLIST_HEAD(file_lock_list);
> -
> -/* Protects the file_lock_list and the blocked_hash */
> static DEFINE_SPINLOCK(file_lock_lock);
> +static HLIST_HEAD(file_lock_list);
>
> static struct kmem_cache *filelock_cache __read_mostly;
>
> @@ -505,9 +504,9 @@ __locks_delete_global_blocked(struct file_lock *waiter)
> static inline void
> locks_delete_global_blocked(struct file_lock *waiter)
> {
> - spin_lock(&file_lock_lock);
> + spin_lock(&blocked_hash_lock);
> __locks_delete_global_blocked(waiter);
> - spin_unlock(&file_lock_lock);
> + spin_unlock(&blocked_hash_lock);
> }
>
> static inline void
> @@ -581,14 +580,14 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
>
> /*
> * Wake up processes blocked waiting for blocker. In the FL_POSIX case, we must
> - * also take the global file_lock_lock and dequeue it from the global blocked
> - * list as we wake the processes.
> + * also take the global blocked_hash_lock and dequeue it from the global
> + * blocked list as we wake the processes.
> *
> * Must be called with the inode->i_lock of the blocker held!
> */
> static void locks_wake_up_posix_blocks(struct file_lock *blocker)
> {
> - spin_lock(&file_lock_lock);
> + spin_lock(&blocked_hash_lock);
> while (!list_empty(&blocker->fl_block)) {
> struct file_lock *waiter;
>
> @@ -601,7 +600,7 @@ static void locks_wake_up_posix_blocks(struct file_lock *blocker)
> else
> wake_up(&waiter->fl_wait);
> }
> - spin_unlock(&file_lock_lock);
> + spin_unlock(&blocked_hash_lock);
> }
> /* Insert file lock fl into an inode's lock list at the position indicated
> * by pos. At the same time add the lock to the global file lock list.
> @@ -754,7 +753,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
> return NULL;
> }
>
> -/* Must be called with the file_lock_lock held! */
> +/* Must be called with the blocked_hash_lock held! */
> static int posix_locks_deadlock(struct file_lock *caller_fl,
> struct file_lock *block_fl)
> {
> @@ -898,13 +897,13 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
> if (!(request->fl_flags & FL_SLEEP))
> goto out;
> error = -EDEADLK;
> - spin_lock(&file_lock_lock);
> + spin_lock(&blocked_hash_lock);
> if (likely(!posix_locks_deadlock(request, fl))) {
> error = FILE_LOCK_DEFERRED;
> locks_insert_block(fl, request);
> locks_insert_global_blocked(request);
> }
> - spin_unlock(&file_lock_lock);
> + spin_unlock(&blocked_hash_lock);
> goto out;
> }
> }
> @@ -2309,10 +2308,12 @@ static int locks_show(struct seq_file *f, void *v)
>
> lock_get_status(f, fl, *((loff_t *)f->private), "");
>
> + spin_lock(&blocked_hash_lock);
> hash_for_each(blocked_hash, bkt, bfl, fl_link) {
> if (bfl->fl_next == fl)
> lock_get_status(f, bfl, *((loff_t *)f->private), " ->");
> }
> + spin_unlock(&blocked_hash_lock);
>
> return 0;
> }
> --
> 1.7.1
>
--
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