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BACKGROUND ========== When multiple work items are queued to a workqueue, their execution order doesn't match the queueing order. They may get executed in any order and simultaneously. When fully serialized execution - one by one in the queueing order - is needed, an ordered workqueue should be used which can be created with alloc_ordered_workqueue(). However, alloc_ordered_workqueue() was a later addition. Before it, an ordered workqueue could be obtained by creating an UNBOUND workqueue with @max_active==1. This originally was an implementation side-effect which was broken by4c16bd327c("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered"). Because there were users that depended on the ordered execution,5c0338c687("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") made workqueue allocation path to implicitly promote UNBOUND workqueues w/ @max_active==1 to ordered workqueues. While this has worked okay, overloading the UNBOUND allocation interface this way creates other issues. It's difficult to tell whether a given workqueue actually needs to be ordered and users that legitimately want a min concurrency level wq unexpectedly gets an ordered one instead. With planned UNBOUND workqueue updates to improve execution locality and more prevalence of chiplet designs which can benefit from such improvements, this isn't a state we wanna be in forever. This patch series audits all call sites that create an UNBOUND workqueue w/ @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. BTRFS ===== * fs_info->scrub_workers initialized in scrub_workers_get() was setting @max_active to 1 when @is_dev_replace is set and it seems that the workqueue actually needs to be ordered if @is_dev_replace. Update the code so that alloc_ordered_workqueue() is used if @is_dev_replace. * fs_info->discard_ctl.discard_workers initialized in btrfs_init_workqueues() was directly using alloc_workqueue() w/ @max_active==1. Converted to alloc_ordered_workqueue(). * fs_info->fixup_workers and fs_info->qgroup_rescan_workers initialized in btrfs_queue_work() use the btrfs's workqueue wrapper, btrfs_workqueue, which are allocated with btrfs_alloc_workqueue(). btrfs_workqueue implements automatic @max_active adjustment which is disabled when the specified max limit is below a certain threshold, so calling btrfs_alloc_workqueue() with @limit_active==1 yields an ordered workqueue whose @max_active won't be changed as the auto-tuning is disabled. This is rather brittle in that nothing clearly indicates that the two workqueues should be ordered or btrfs_alloc_workqueue() must disable auto-tuning when @limit_active==1. This patch factors out the common btrfs_workqueue init code into btrfs_init_workqueue() and add explicit btrfs_alloc_ordered_workqueue(). The two workqueues are converted to use the new ordered allocation interface. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: David Sterba <dsterba@suse.com>
49 lines
1.5 KiB
C
49 lines
1.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2007 Oracle. All rights reserved.
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* Copyright (C) 2014 Fujitsu. All rights reserved.
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*/
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#ifndef BTRFS_ASYNC_THREAD_H
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#define BTRFS_ASYNC_THREAD_H
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#include <linux/workqueue.h>
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struct btrfs_fs_info;
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struct btrfs_workqueue;
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struct btrfs_work;
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typedef void (*btrfs_func_t)(struct btrfs_work *arg);
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struct btrfs_work {
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btrfs_func_t func;
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btrfs_func_t ordered_func;
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btrfs_func_t ordered_free;
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/* Don't touch things below */
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struct work_struct normal_work;
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struct list_head ordered_list;
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struct btrfs_workqueue *wq;
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unsigned long flags;
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};
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struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
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const char *name,
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unsigned int flags,
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int limit_active,
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int thresh);
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struct btrfs_workqueue *btrfs_alloc_ordered_workqueue(
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struct btrfs_fs_info *fs_info, const char *name,
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unsigned int flags);
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void btrfs_init_work(struct btrfs_work *work, btrfs_func_t func,
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btrfs_func_t ordered_func, btrfs_func_t ordered_free);
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void btrfs_queue_work(struct btrfs_workqueue *wq,
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struct btrfs_work *work);
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void btrfs_destroy_workqueue(struct btrfs_workqueue *wq);
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void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max);
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struct btrfs_fs_info * __pure btrfs_work_owner(const struct btrfs_work *work);
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struct btrfs_fs_info * __pure btrfs_workqueue_owner(const struct btrfs_workqueue *wq);
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bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq);
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void btrfs_flush_workqueue(struct btrfs_workqueue *wq);
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#endif
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