b4ce94de9b
Most of the btrfs metadata operations can be protected by a spinlock, but some operations still need to schedule. So far, btrfs has been using a mutex along with a trylock loop, most of the time it is able to avoid going for the full mutex, so the trylock loop is a big performance gain. This commit is step one for getting rid of the blocking locks entirely. btrfs_tree_lock takes a spinlock, and the code explicitly switches to a blocking lock when it starts an operation that can schedule. We'll be able get rid of the blocking locks in smaller pieces over time. Tracing allows us to find the most common cause of blocking, so we can start with the hot spots first. The basic idea is: btrfs_tree_lock() returns with the spin lock held btrfs_set_lock_blocking() sets the EXTENT_BUFFER_BLOCKING bit in the extent buffer flags, and then drops the spin lock. The buffer is still considered locked by all of the btrfs code. If btrfs_tree_lock gets the spinlock but finds the blocking bit set, it drops the spin lock and waits on a wait queue for the blocking bit to go away. Much of the code that needs to set the blocking bit finishes without actually blocking a good percentage of the time. So, an adaptive spin is still used against the blocking bit to avoid very high context switch rates. btrfs_clear_lock_blocking() clears the blocking bit and returns with the spinlock held again. btrfs_tree_unlock() can be called on either blocking or spinning locks, it does the right thing based on the blocking bit. ctree.c has a helper function to set/clear all the locked buffers in a path as blocking. Signed-off-by: Chris Mason <chris.mason@oracle.com>
149 lines
3.6 KiB
C
149 lines
3.6 KiB
C
/*
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* Copyright (C) 2007 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 "ctree.h"
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#include "disk-io.h"
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#include "print-tree.h"
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#include "transaction.h"
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#include "locking.h"
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/* defrag all the leaves in a given btree. If cache_only == 1, don't read
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* things from disk, otherwise read all the leaves and try to get key order to
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* better reflect disk order
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*/
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int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
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struct btrfs_root *root, int cache_only)
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{
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struct btrfs_path *path = NULL;
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struct btrfs_key key;
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int ret = 0;
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int wret;
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int level;
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int orig_level;
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int is_extent = 0;
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int next_key_ret = 0;
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u64 last_ret = 0;
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u64 min_trans = 0;
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if (cache_only)
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goto out;
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if (root->fs_info->extent_root == root) {
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/*
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* there's recursion here right now in the tree locking,
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* we can't defrag the extent root without deadlock
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*/
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goto out;
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}
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if (root->ref_cows == 0 && !is_extent)
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goto out;
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if (btrfs_test_opt(root, SSD))
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goto out;
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path = btrfs_alloc_path();
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if (!path)
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return -ENOMEM;
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level = btrfs_header_level(root->node);
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orig_level = level;
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if (level == 0)
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goto out;
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if (root->defrag_progress.objectid == 0) {
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struct extent_buffer *root_node;
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u32 nritems;
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root_node = btrfs_lock_root_node(root);
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btrfs_set_lock_blocking(root_node);
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nritems = btrfs_header_nritems(root_node);
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root->defrag_max.objectid = 0;
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/* from above we know this is not a leaf */
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btrfs_node_key_to_cpu(root_node, &root->defrag_max,
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nritems - 1);
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btrfs_tree_unlock(root_node);
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free_extent_buffer(root_node);
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memset(&key, 0, sizeof(key));
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} else {
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memcpy(&key, &root->defrag_progress, sizeof(key));
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}
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path->keep_locks = 1;
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if (cache_only)
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min_trans = root->defrag_trans_start;
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ret = btrfs_search_forward(root, &key, NULL, path,
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cache_only, min_trans);
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if (ret < 0)
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goto out;
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if (ret > 0) {
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ret = 0;
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goto out;
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}
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btrfs_release_path(root, path);
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wret = btrfs_search_slot(trans, root, &key, path, 0, 1);
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if (wret < 0) {
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ret = wret;
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goto out;
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}
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if (!path->nodes[1]) {
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ret = 0;
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goto out;
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}
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path->slots[1] = btrfs_header_nritems(path->nodes[1]);
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next_key_ret = btrfs_find_next_key(root, path, &key, 1, cache_only,
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min_trans);
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ret = btrfs_realloc_node(trans, root,
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path->nodes[1], 0,
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cache_only, &last_ret,
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&root->defrag_progress);
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WARN_ON(ret && ret != -EAGAIN);
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if (next_key_ret == 0) {
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memcpy(&root->defrag_progress, &key, sizeof(key));
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ret = -EAGAIN;
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}
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btrfs_release_path(root, path);
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if (is_extent)
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btrfs_extent_post_op(trans, root);
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out:
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if (path)
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btrfs_free_path(path);
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if (ret == -EAGAIN) {
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if (root->defrag_max.objectid > root->defrag_progress.objectid)
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goto done;
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if (root->defrag_max.type > root->defrag_progress.type)
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goto done;
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if (root->defrag_max.offset > root->defrag_progress.offset)
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goto done;
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ret = 0;
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}
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done:
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if (ret != -EAGAIN) {
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memset(&root->defrag_progress, 0,
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sizeof(root->defrag_progress));
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root->defrag_trans_start = trans->transid;
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}
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return ret;
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}
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