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locks: turn the blocked_list into a hashtable

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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@redhat.com>
Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jeff Layton 2013-06-21 08:58:18 -04:00 committed by Al Viro
parent 139ca04ee5
commit 48f7418654
1 changed files with 17 additions and 8 deletions
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25
fs/locks.c
View file

@ -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) {