[PATCH v3 09/13] locks: turn the blocked_list into a hashtable

From: Jeff Layton
Date: Mon Jun 17 2013 - 11:17:56 EST

Break up the blocked_list into a hashtable, using the fl_owner as a key.
This speeds up searching the hash chains, which is especially significant
for deadlock detection.

Note that the initial implementation assumes that hashing on fl_owner is
sufficient. In most cases it should be, with the notable exception being
server-side lockd, which compares ownership using a tuple of the
nlm_host and the pid sent in the lock request. So, this may degrade to a
single hash bucket when you only have a single NFS client. That will be
addressed in a later patch.

The careful observer may note that this patch leaves the file_lock_list
alone. There's much less of a case for turning the file_lock_list into a
hashtable. The only user of that list is the code that generates
/proc/locks, and it always walks the entire list.

Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Acked-by: J. Bruce Fields <bfields@xxxxxxxxxxxx>
fs/locks.c | 25 +++++++++++++++++--------
1 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 32826ed..d93b291 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -126,6 +126,7 @@
#include <linux/time.h>
#include <linux/rcupdate.h>
#include <linux/pid_namespace.h>
+#include <linux/hashtable.h>

#include <asm/uaccess.h>

@@ -160,12 +161,20 @@ int lease_break_time = 45;
static HLIST_HEAD(file_lock_list);

- * The blocked_list is used to find POSIX lock loops for deadlock detection.
- * Protected by file_lock_lock.
+ * The blocked_hash is used to find POSIX lock loops for deadlock detection.
+ * It is protected by file_lock_lock.
+ *
+ * We hash locks by lockowner in order to optimize searching for the lock a
+ * particular lockowner is waiting on.
+ *
+ * FIXME: make this value scale via some heuristic? We generally will want more
+ * buckets when we have more lockowners holding locks, but that's a little
+ * difficult to determine without knowing what the workload will look like.
-static HLIST_HEAD(blocked_list);

-/* Protects the two list heads above, and fl->fl_block list. */
+/* Protects the file_lock_list, the blocked_hash and fl->fl_block list */
static DEFINE_SPINLOCK(file_lock_lock);

static struct kmem_cache *filelock_cache __read_mostly;
@@ -499,13 +508,13 @@ locks_delete_global_locks(struct file_lock *waiter)
static inline void
locks_insert_global_blocked(struct file_lock *waiter)
- hlist_add_head(&waiter->fl_link, &blocked_list);
+ hash_add(blocked_hash, &waiter->fl_link, (unsigned long)waiter->fl_owner);

static inline void
locks_delete_global_blocked(struct file_lock *waiter)
- hlist_del_init(&waiter->fl_link);
+ hash_del(&waiter->fl_link);

/* Remove waiter from blocker's block list.
@@ -730,7 +739,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
struct file_lock *fl;

- hlist_for_each_entry(fl, &blocked_list, fl_link) {
+ hash_for_each_possible(blocked_hash, fl, fl_link, (unsigned long)block_fl->fl_owner) {
if (posix_same_owner(fl, block_fl))
return fl->fl_next;
@@ -866,7 +875,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
* New lock request. Walk all POSIX locks and look for conflicts. If
* there are any, either return error or put the request on the
- * blocker's list of waiters and the global blocked_list.
+ * blocker's list of waiters and the global blocked_hash.
if (request->fl_type != F_UNLCK) {
for_each_lock(inode, before) {

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