path: root/fs/fs-writeback.c

/*
 * fs/fs-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * Contains all the functions related to writing back and waiting
 * upon dirty inodes against superblocks, and writing back dirty
 * pages against inodes.  ie: data writeback.  Writeout of the
 * inode itself is not handled here.
 *
 * 10Apr2002	Andrew Morton
 *		Split out of fs/inode.c
 *		Additions for address_space-based writeback
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
#include "internal.h"

#define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)

/*
 * We don't actually have pdflush, but this one is exported though /proc...
 */
int nr_pdflush_threads;

/*
 * Passed into wb_writeback(), essentially a subset of writeback_control
 */
struct wb_writeback_args {
	long nr_pages;
	struct super_block *sb;
	enum writeback_sync_modes sync_mode;
	int for_kupdate;
	int range_cyclic;
};

/*
 * Work items for the bdi_writeback threads
 */
struct bdi_work {
	struct list_head list;		/* pending work list */
	struct rcu_head rcu_head;	/* for RCU free/clear of work */

	unsigned long seen;		/* threads that have seen this work */
	atomic_t pending;		/* number of threads still to do work */

	struct wb_writeback_args args;	/* writeback arguments */

	unsigned long state;		/* flag bits, see WS_* */
};

enum {
	WS_USED_B = 0,
	WS_ONSTACK_B,
};

#define WS_USED (1 << WS_USED_B)
#define WS_ONSTACK (1 << WS_ONSTACK_B)

static inline bool bdi_work_on_stack(struct bdi_work *work)
{
	return test_bit(WS_ONSTACK_B, &work->state);
}

static inline void bdi_work_init(struct bdi_work *work,
				 struct wb_writeback_args *args)
{
	INIT_RCU_HEAD(&work->rcu_head);
	work->args = *args;
	work->state = WS_USED;
}

/**
 * writeback_in_progress - determine whether there is writeback in progress
 * @bdi: the device's backing_dev_info structure.
 *
 * Determine whether there is writeback waiting to be handled against a
 * backing device.
 */
int writeback_in_progress(struct backing_dev_info *bdi)
{
	return !list_empty(&bdi->work_list);
}

static void bdi_work_clear(struct bdi_work *work)
{
	clear_bit(WS_USED_B, &work->state);
	smp_mb__after_clear_bit();
	wake_up_bit(&work->state, WS_USED_B);
}

static void bdi_work_free(struct rcu_head *head)
{
	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);

	if (!bdi_work_on_stack(work))
		kfree(work);
	else
		bdi_work_clear(work);
}

static void wb_work_complete(struct bdi_work *work)
{
	const enum writeback_sync_modes sync_mode = work->args.sync_mode;

	/*
	 * For allocated work, we can clear the done/seen bit right here.
	 * For on-stack work, we need to postpone both the clear and free
	 * to after the RCU grace period, since the stack could be invalidated
	 * as soon as bdi_work_clear() has done the wakeup.
	 */
	if (!bdi_work_on_stack(work))
		bdi_work_clear(work);
	if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
		call_rcu(&work->rcu_head, bdi_work_free);
}

static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
{
	/*
	 * The caller has retrieved the work arguments from this work,
	 * drop our reference. If this is the last ref, delete and free it
	 */
	if (atomic_dec_and_test(&work->pending)) {