Commit 48f74186 authored by Jeff Layton's avatar Jeff Layton Committed by Al Viro
Browse files

locks: turn the blocked_list into a hashtable 



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: default avatarJeff Layton <jlayton@redhat.com>
Acked-by: default avatarJ. Bruce Fields <bfields@fieldses.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 139ca04e

fs/locks.c

+17 −8
Original line number Diff line number Diff line
@@ -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>
@@ -160,13 +161,21 @@ 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);

#define BLOCKED_HASH_BITS	7

static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);



/*

 * This lock protects the blocked_list, and the file_lock_list. Generally, if

 * This lock protects the blocked_hash and the file_lock_list. Generally, if

 * you're accessing one of those lists, you want to be holding this lock.

 *

 * In addition, it also protects the fl->fl_block list, and the fl->fl_next
@@ -515,13 +524,13 @@ locks_delete_global_locks(struct file_lock *fl) 
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.
@@ -748,7 +757,7 @@ 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;

	}
@@ -884,7 +893,7 @@ 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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