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/*
* Copyright (C) 2008 Oracle. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#include <linux/sched.h>
#include <linux/gfp.h>
#include <linux/pagemap.h>
#include <linux/spinlock.h>
#include <linux/page-flags.h>
#include <asm/bug.h>
#include "ctree.h"
#include "extent_io.h"
#include "locking.h"
/*
* locks the per buffer mutex in an extent buffer. This uses adaptive locks
* and the spin is not tuned very extensively. The spinning does make a big
* difference in almost every workload, but spinning for the right amount of
* time needs some help.
*
* In general, we want to spin as long as the lock holder is doing btree searches,
* and we should give up if they are in more expensive code.
*/
int btrfs_tree_lock(struct extent_buffer *eb)
{
int i;
if (mutex_trylock(&eb->mutex))
return 0;
for (i = 0; i < 512; i++) {
cpu_relax();
if (mutex_trylock(&eb->mutex))
return 0;
}
cpu_relax();
mutex_lock_nested(&eb->mutex, BTRFS_MAX_LEVEL - btrfs_header_level(eb));
return 0;
}
int btrfs_try_tree_lock(struct extent_buffer *eb)
{
return mutex_trylock(&eb->mutex);
}
int btrfs_tree_unlock(struct extent_buffer *eb)
{
mutex_unlock(&eb->mutex);
return 0;
}
int btrfs_tree_locked(struct extent_buffer *eb)
{
return mutex_is_locked(&eb->mutex);
}
/*
* btrfs_search_slot uses this to decide if it should drop its locks
* before doing something expensive like allocating free blocks for cow.
*/
int btrfs_path_lock_waiting(struct btrfs_path *path, int level)
{
int i;
struct extent_buffer *eb;
for (i = level; i <= level + 1 && i < BTRFS_MAX_LEVEL; i++) {
eb = path->nodes[i];
if (!eb)
break;
smp_mb();
if (!list_empty(&eb->mutex.wait_list))
return 1;
}
return 0;
}
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