writeback: eliminate work item allocation in bd_start_writeback() (85009b4f) · Commits · 戴 / test

fs/fs-writeback.c

+34 −37

Original line number	Diff line number	Diff line
		@@ -53,7 +53,6 @@ struct wb_writeback_work {
		unsigned int for_background:1;
		unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
		unsigned int auto_free:1; /* free on completion */
		unsigned int start_all:1; /* nr_pages == 0 (all) writeback */
		enum wb_reason reason; /* why was writeback initiated? */

		struct list_head list; /* pending work list */
		@@ -947,8 +946,6 @@ static unsigned long get_nr_dirty_pages(void)

		static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
		{
		struct wb_writeback_work *work;

		if (!wb_has_dirty_io(wb))
		return;

		@@ -958,35 +955,14 @@ static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
		* high frequency, causing pointless allocations of tons of
		* work items and keeping the flusher threads busy retrieving
		* that work. Ensure that we only allow one of them pending and
		* inflight at the time. It doesn't matter if we race a little
		* bit on this, so use the faster separate test/set bit variants.
		* inflight at the time.
		*/
		if (test_bit(WB_start_all, &wb->state))
		if (test_bit(WB_start_all, &wb->state) \|\|
		test_and_set_bit(WB_start_all, &wb->state))
		return;

		set_bit(WB_start_all, &wb->state);

		/*
		* This is WB_SYNC_NONE writeback, so if allocation fails just
		* wakeup the thread for old dirty data writeback
		*/
		work = kzalloc(sizeof(*work),
		GFP_NOWAIT \| __GFP_NOMEMALLOC \| __GFP_NOWARN);
		if (!work) {
		clear_bit(WB_start_all, &wb->state);
		trace_writeback_nowork(wb);
		wb->start_all_reason = reason;
		wb_wakeup(wb);
		return;
		}

		work->sync_mode = WB_SYNC_NONE;
		work->nr_pages = wb_split_bdi_pages(wb, get_nr_dirty_pages());
		work->range_cyclic = 1;
		work->reason = reason;
		work->auto_free = 1;
		work->start_all = 1;

		wb_queue_work(wb, work);
		}

		/**
		@@ -1838,14 +1814,6 @@ static struct wb_writeback_work get_next_work_item(struct bdi_writeback wb)
		list_del_init(&work->list);
		}
		spin_unlock_bh(&wb->work_lock);

		/*
		* Once we start processing a work item that had !nr_pages,
		* clear the wb state bit for that so we can allow more.
		*/
		if (work && work->start_all)
		clear_bit(WB_start_all, &wb->state);

		return work;
		}

		@@ -1901,6 +1869,30 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
		return 0;
		}

		static long wb_check_start_all(struct bdi_writeback *wb)
		{
		long nr_pages;

		if (!test_bit(WB_start_all, &wb->state))
		return 0;

		nr_pages = get_nr_dirty_pages();
		if (nr_pages) {
		struct wb_writeback_work work = {
		.nr_pages = wb_split_bdi_pages(wb, nr_pages),
		.sync_mode = WB_SYNC_NONE,
		.range_cyclic = 1,
		.reason = wb->start_all_reason,
		};

		nr_pages = wb_writeback(wb, &work);
		}

		clear_bit(WB_start_all, &wb->state);
		return nr_pages;
		}


		/*
		* Retrieve work items and do the writeback they describe
		*/
		@@ -1916,6 +1908,11 @@ static long wb_do_writeback(struct bdi_writeback *wb)
		finish_writeback_work(wb, work);
		}

		/*
		* Check for a flush-everything request
		*/
		wrote += wb_check_start_all(wb);

		/*
		* Check for periodic writeback, kupdated() style
		*/

include/linux/backing-dev-defs.h

+23 −0

Original line number	Diff line number	Diff line
		@@ -44,6 +44,28 @@ enum wb_stat_item {

		#define WB_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))

		/*
		* why some writeback work was initiated
		*/
		enum wb_reason {
		WB_REASON_BACKGROUND,
		WB_REASON_VMSCAN,
		WB_REASON_SYNC,
		WB_REASON_PERIODIC,
		WB_REASON_LAPTOP_TIMER,
		WB_REASON_FREE_MORE_MEM,
		WB_REASON_FS_FREE_SPACE,
		/*
		* There is no bdi forker thread any more and works are done
		* by emergency worker, however, this is TPs userland visible
		* and we'll be exposing exactly the same information,
		* so it has a mismatch name.
		*/
		WB_REASON_FORKER_THREAD,

		WB_REASON_MAX,
		};

		/*
		* For cgroup writeback, multiple wb's may map to the same blkcg. Those
		* wb's can operate mostly independently but should share the congested
		@@ -116,6 +138,7 @@ struct bdi_writeback {

		struct fprop_local_percpu completions;
		int dirty_exceeded;
		enum wb_reason start_all_reason;

		spinlock_t work_lock; /* protects work_list & dwork scheduling */
		struct list_head work_list;

include/linux/writeback.h

+0 −22

Original line number	Diff line number	Diff line
		@@ -41,28 +41,6 @@ enum writeback_sync_modes {
		WB_SYNC_ALL, /* Wait on every mapping */
		};

		/*
		* why some writeback work was initiated
		*/
		enum wb_reason {
		WB_REASON_BACKGROUND,
		WB_REASON_VMSCAN,
		WB_REASON_SYNC,
		WB_REASON_PERIODIC,
		WB_REASON_LAPTOP_TIMER,
		WB_REASON_FREE_MORE_MEM,
		WB_REASON_FS_FREE_SPACE,
		/*
		* There is no bdi forker thread any more and works are done
		* by emergency worker, however, this is TPs userland visible
		* and we'll be exposing exactly the same information,
		* so it has a mismatch name.
		*/
		WB_REASON_FORKER_THREAD,

		WB_REASON_MAX,
		};

		/*
		* A control structure which tells the writeback code what to do. These are
		* always on the stack, and hence need no locking. They are always initialised

include/trace/events/writeback.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -286,7 +286,6 @@ DEFINE_EVENT(writeback_class, name, \
		TP_PROTO(struct bdi_writeback *wb), \
		TP_ARGS(wb))

		DEFINE_WRITEBACK_EVENT(writeback_nowork);
		DEFINE_WRITEBACK_EVENT(writeback_wake_background);

		TRACE_EVENT(writeback_bdi_register,

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