Btrfs: improve the delayed inode throttling
The delayed inode code batches up changes to the btree in hopes of doing
them in bulk. As the changes build up, processes kick off worker
threads and wait for them to make progress.
The current code kicks off an async work queue item for each delayed
node, which creates a lot of churn. It also uses a fixed 1 HZ waiting
period for the throttle, which allows us to build a lot of pending
work and can slow down the commit.
This changes us to watch a sequence counter as it is bumped during the
operations. We kick off fewer work items and have each work item do
more work.
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 0b278b1..14fce27 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -22,8 +22,9 @@
#include "disk-io.h"
#include "transaction.h"
-#define BTRFS_DELAYED_WRITEBACK 400
-#define BTRFS_DELAYED_BACKGROUND 100
+#define BTRFS_DELAYED_WRITEBACK 512
+#define BTRFS_DELAYED_BACKGROUND 128
+#define BTRFS_DELAYED_BATCH 16
static struct kmem_cache *delayed_node_cache;
@@ -494,6 +495,15 @@
BTRFS_DELAYED_DELETION_ITEM);
}
+static void finish_one_item(struct btrfs_delayed_root *delayed_root)
+{
+ int seq = atomic_inc_return(&delayed_root->items_seq);
+ if ((atomic_dec_return(&delayed_root->items) <
+ BTRFS_DELAYED_BACKGROUND || seq % BTRFS_DELAYED_BATCH == 0) &&
+ waitqueue_active(&delayed_root->wait))
+ wake_up(&delayed_root->wait);
+}
+
static void __btrfs_remove_delayed_item(struct btrfs_delayed_item *delayed_item)
{
struct rb_root *root;
@@ -512,10 +522,8 @@
rb_erase(&delayed_item->rb_node, root);
delayed_item->delayed_node->count--;
- if (atomic_dec_return(&delayed_root->items) <
- BTRFS_DELAYED_BACKGROUND &&
- waitqueue_active(&delayed_root->wait))
- wake_up(&delayed_root->wait);
+
+ finish_one_item(delayed_root);
}
static void btrfs_release_delayed_item(struct btrfs_delayed_item *item)
@@ -1056,10 +1064,7 @@
delayed_node->count--;
delayed_root = delayed_node->root->fs_info->delayed_root;
- if (atomic_dec_return(&delayed_root->items) <
- BTRFS_DELAYED_BACKGROUND &&
- waitqueue_active(&delayed_root->wait))
- wake_up(&delayed_root->wait);
+ finish_one_item(delayed_root);
}
}
@@ -1304,35 +1309,44 @@
btrfs_release_delayed_node(delayed_node);
}
-struct btrfs_async_delayed_node {
- struct btrfs_root *root;
- struct btrfs_delayed_node *delayed_node;
+struct btrfs_async_delayed_work {
+ struct btrfs_delayed_root *delayed_root;
+ int nr;
struct btrfs_work work;
};
-static void btrfs_async_run_delayed_node_done(struct btrfs_work *work)
+static void btrfs_async_run_delayed_root(struct btrfs_work *work)
{
- struct btrfs_async_delayed_node *async_node;
+ struct btrfs_async_delayed_work *async_work;
+ struct btrfs_delayed_root *delayed_root;
struct btrfs_trans_handle *trans;
struct btrfs_path *path;
struct btrfs_delayed_node *delayed_node = NULL;
struct btrfs_root *root;
struct btrfs_block_rsv *block_rsv;
- int need_requeue = 0;
+ int total_done = 0;
- async_node = container_of(work, struct btrfs_async_delayed_node, work);
+ async_work = container_of(work, struct btrfs_async_delayed_work, work);
+ delayed_root = async_work->delayed_root;
path = btrfs_alloc_path();
if (!path)
goto out;
- path->leave_spinning = 1;
- delayed_node = async_node->delayed_node;
+again:
+ if (atomic_read(&delayed_root->items) < BTRFS_DELAYED_BACKGROUND / 2)
+ goto free_path;
+
+ delayed_node = btrfs_first_prepared_delayed_node(delayed_root);
+ if (!delayed_node)
+ goto free_path;
+
+ path->leave_spinning = 1;
root = delayed_node->root;
trans = btrfs_join_transaction(root);
if (IS_ERR(trans))
- goto free_path;
+ goto release_path;
block_rsv = trans->block_rsv;
trans->block_rsv = &root->fs_info->delayed_block_rsv;
@@ -1363,57 +1377,47 @@
* Task1 will sleep until the transaction is commited.
*/
mutex_lock(&delayed_node->mutex);
- if (delayed_node->count)
- need_requeue = 1;
- else
- btrfs_dequeue_delayed_node(root->fs_info->delayed_root,
- delayed_node);
+ btrfs_dequeue_delayed_node(root->fs_info->delayed_root, delayed_node);
mutex_unlock(&delayed_node->mutex);
trans->block_rsv = block_rsv;
btrfs_end_transaction_dmeta(trans, root);
btrfs_btree_balance_dirty_nodelay(root);
+
+release_path:
+ btrfs_release_path(path);
+ total_done++;
+
+ btrfs_release_prepared_delayed_node(delayed_node);
+ if (async_work->nr == 0 || total_done < async_work->nr)
+ goto again;
+
free_path:
btrfs_free_path(path);
out:
- if (need_requeue)
- btrfs_requeue_work(&async_node->work);
- else {
- btrfs_release_prepared_delayed_node(delayed_node);
- kfree(async_node);
- }
+ wake_up(&delayed_root->wait);
+ kfree(async_work);
}
-static int btrfs_wq_run_delayed_node(struct btrfs_delayed_root *delayed_root,
- struct btrfs_root *root, int all)
-{
- struct btrfs_async_delayed_node *async_node;
- struct btrfs_delayed_node *curr;
- int count = 0;
-again:
- curr = btrfs_first_prepared_delayed_node(delayed_root);
- if (!curr)
+static int btrfs_wq_run_delayed_node(struct btrfs_delayed_root *delayed_root,
+ struct btrfs_root *root, int nr)
+{
+ struct btrfs_async_delayed_work *async_work;
+
+ if (atomic_read(&delayed_root->items) < BTRFS_DELAYED_BACKGROUND)
return 0;
- async_node = kmalloc(sizeof(*async_node), GFP_NOFS);
- if (!async_node) {
- btrfs_release_prepared_delayed_node(curr);
+ async_work = kmalloc(sizeof(*async_work), GFP_NOFS);
+ if (!async_work)
return -ENOMEM;
- }
- async_node->root = root;
- async_node->delayed_node = curr;
+ async_work->delayed_root = delayed_root;
+ async_work->work.func = btrfs_async_run_delayed_root;
+ async_work->work.flags = 0;
+ async_work->nr = nr;
- async_node->work.func = btrfs_async_run_delayed_node_done;
- async_node->work.flags = 0;
-
- btrfs_queue_worker(&root->fs_info->delayed_workers, &async_node->work);
- count++;
-
- if (all || count < 4)
- goto again;
-
+ btrfs_queue_worker(&root->fs_info->delayed_workers, &async_work->work);
return 0;
}
@@ -1424,30 +1428,55 @@
WARN_ON(btrfs_first_delayed_node(delayed_root));
}
+static int refs_newer(struct btrfs_delayed_root *delayed_root,
+ int seq, int count)
+{
+ int val = atomic_read(&delayed_root->items_seq);
+
+ if (val < seq || val >= seq + count)
+ return 1;
+ return 0;
+}
+
void btrfs_balance_delayed_items(struct btrfs_root *root)
{
struct btrfs_delayed_root *delayed_root;
+ int seq;
delayed_root = btrfs_get_delayed_root(root);
if (atomic_read(&delayed_root->items) < BTRFS_DELAYED_BACKGROUND)
return;
+ seq = atomic_read(&delayed_root->items_seq);
+
if (atomic_read(&delayed_root->items) >= BTRFS_DELAYED_WRITEBACK) {
int ret;
- ret = btrfs_wq_run_delayed_node(delayed_root, root, 1);
+ DEFINE_WAIT(__wait);
+
+ ret = btrfs_wq_run_delayed_node(delayed_root, root, 0);
if (ret)
return;
- wait_event_interruptible_timeout(
- delayed_root->wait,
- (atomic_read(&delayed_root->items) <
- BTRFS_DELAYED_BACKGROUND),
- HZ);
- return;
+ while (1) {
+ prepare_to_wait(&delayed_root->wait, &__wait,
+ TASK_INTERRUPTIBLE);
+
+ if (refs_newer(delayed_root, seq,
+ BTRFS_DELAYED_BATCH) ||
+ atomic_read(&delayed_root->items) <
+ BTRFS_DELAYED_BACKGROUND) {
+ break;
+ }
+ if (!signal_pending(current))
+ schedule();
+ else
+ break;
+ }
+ finish_wait(&delayed_root->wait, &__wait);
}
- btrfs_wq_run_delayed_node(delayed_root, root, 0);
+ btrfs_wq_run_delayed_node(delayed_root, root, BTRFS_DELAYED_BATCH);
}
/* Will return 0 or -ENOMEM */
diff --git a/fs/btrfs/delayed-inode.h b/fs/btrfs/delayed-inode.h
index 78b6ad0..1d5c5f7 100644
--- a/fs/btrfs/delayed-inode.h
+++ b/fs/btrfs/delayed-inode.h
@@ -43,6 +43,7 @@
*/
struct list_head prepare_list;
atomic_t items; /* for delayed items */
+ atomic_t items_seq; /* for delayed items */
int nodes; /* for delayed nodes */
wait_queue_head_t wait;
};
@@ -86,6 +87,7 @@
struct btrfs_delayed_root *delayed_root)
{
atomic_set(&delayed_root->items, 0);
+ atomic_set(&delayed_root->items_seq, 0);
delayed_root->nodes = 0;
spin_lock_init(&delayed_root->lock);
init_waitqueue_head(&delayed_root->wait);
