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d352ac6814
This improves the comments at the top of many functions. It didn't dive into the guts of functions because I was trying to avoid merging problems with the new allocator and back reference work. extent-tree.c and volumes.c were both skipped, and there is definitely more work todo in cleaning and commenting the code. Signed-off-by: Chris Mason <chris.mason@oracle.com>
88 lines
2.3 KiB
C
88 lines
2.3 KiB
C
/*
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* Copyright (C) 2008 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#include <linux/sched.h>
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#include <linux/gfp.h>
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#include <linux/pagemap.h>
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#include <linux/spinlock.h>
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#include <linux/page-flags.h>
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#include <asm/bug.h>
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#include "ctree.h"
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#include "extent_io.h"
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#include "locking.h"
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/*
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* locks the per buffer mutex in an extent buffer. This uses adaptive locks
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* and the spin is not tuned very extensively. The spinning does make a big
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* difference in almost every workload, but spinning for the right amount of
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* time needs some help.
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*
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* In general, we want to spin as long as the lock holder is doing btree searches,
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* and we should give up if they are in more expensive code.
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*/
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int btrfs_tree_lock(struct extent_buffer *eb)
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{
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int i;
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if (mutex_trylock(&eb->mutex))
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return 0;
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for (i = 0; i < 512; i++) {
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cpu_relax();
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if (mutex_trylock(&eb->mutex))
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return 0;
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}
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cpu_relax();
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mutex_lock_nested(&eb->mutex, BTRFS_MAX_LEVEL - btrfs_header_level(eb));
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return 0;
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}
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int btrfs_try_tree_lock(struct extent_buffer *eb)
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{
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return mutex_trylock(&eb->mutex);
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}
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int btrfs_tree_unlock(struct extent_buffer *eb)
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{
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mutex_unlock(&eb->mutex);
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return 0;
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}
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int btrfs_tree_locked(struct extent_buffer *eb)
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{
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return mutex_is_locked(&eb->mutex);
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}
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/*
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* btrfs_search_slot uses this to decide if it should drop its locks
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* before doing something expensive like allocating free blocks for cow.
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*/
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int btrfs_path_lock_waiting(struct btrfs_path *path, int level)
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{
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int i;
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struct extent_buffer *eb;
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for (i = level; i <= level + 1 && i < BTRFS_MAX_LEVEL; i++) {
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eb = path->nodes[i];
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if (!eb)
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break;
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smp_mb();
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if (!list_empty(&eb->mutex.wait_list))
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return 1;
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}
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return 0;
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}
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