On wed, 6 Mar 2013 09:53:28 -0500, Chris Mason wrote:
> On Tue, Mar 05, 2013 at 07:45:34PM -0700, Miao Xie wrote:
>>
>> We re-queue the node just when there are some delayed items in the current node.
>> But if the node still has delayed items after we deal with it, that is to say
>> someone is accessing the node. So it is better to release it and deal with it
>> later. In this way, we can amass more items and deal with them in batches.
>
> Thanks, I've made this change.
>
>>
>>> + } else {
>>> + btrfs_release_prepared_delayed_node(delayed_node);
>>> + if (async_work->nr == 0 || total_done < async_work->nr)
>>> + goto again;
>>
>> If joining transaction fails, we should end the async handle. And for case
>> ->nr == 0 (it means there are too many items, we need flush all), we can
>> set ->blocked of the current transaction, in this way, the users can not
>> insert any delayed item for a while, and will wait until the current
>> transation is committed
>
> This one I've left out for now, the old code didn't block and I'd prefer
> that we test that change independently.
>
> V2 below, it also has the break Liu Bo mentioned.
>
> From: Chris Mason <chris.mason@xxxxxxxxxxxx>
> Date: Mon, 4 Mar 2013 17:13:31 -0500
> Subject: [PATCH] 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@xxxxxxxxxxxx>
> ---
> fs/btrfs/delayed-inode.c | 152 ++++++++++++++++++++++++++++-------------------
> fs/btrfs/delayed-inode.h | 2 +
> 2 files changed, 94 insertions(+), 60 deletions(-)
>
> diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
> index 0b278b1..46f354a 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 @@ static int __btrfs_add_delayed_deletion_item(struct btrfs_delayed_node *node,
> 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 @@ static void __btrfs_remove_delayed_item(struct btrfs_delayed_item *delayed_item)
>
> 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 @@ static void btrfs_release_delayed_inode(struct btrfs_delayed_node *delayed_node)
> 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 @@ void btrfs_remove_delayed_node(struct inode *inode)
> 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 +1377,50 @@ static void btrfs_async_run_delayed_node_done(struct btrfs_work *work)
> * 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);
The code in this mutex can be removed, this implementation won't trigger
the problem that the comment mentions.
Thanks
Miao
>
> 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_root *root, int nr)
> {
> - struct btrfs_async_delayed_node *async_node;
> - struct btrfs_delayed_node *curr;
> - int count = 0;
> + struct btrfs_async_delayed_work *async_work;
>
> -again:
> - curr = btrfs_first_prepared_delayed_node(delayed_root);
> - if (!curr)
> + 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_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;
> + async_work->delayed_root = delayed_root;
> + async_work->work.func = btrfs_async_run_delayed_root;
> + async_work->work.flags = 0;
> + if (nr)
> + async_work->nr = 0;
> + else
> + async_work->nr = nr;
>
> + btrfs_queue_worker(&root->fs_info->delayed_workers, &async_work->work);
> return 0;
> }
>
> @@ -1424,30 +1431,55 @@ void btrfs_assert_delayed_root_empty(struct btrfs_root *root)
> 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;
> + DEFINE_WAIT(__wait);
> +
> ret = btrfs_wq_run_delayed_node(delayed_root, root, 1);
> 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 btrfs_delayed_root {
> */
> 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 @@ static inline void btrfs_init_delayed_root(
> 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);
>
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