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/slab.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_work {
	long nr_pages;
	struct super_block *sb;
	enum writeback_sync_modes sync_mode;
	unsigned int for_kupdate:1;
	unsigned int range_cyclic:1;
	unsigned int for_background:1;

	struct list_head list;		/* pending work list */
	struct completion *done;	/* set if the caller waits */
};

/**
 * 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_queue_work(struct backing_dev_info *bdi,
		struct wb_writeback_work *work)
{
	spin_lock(&bdi->wb_lock);
	list_add_tail(&work->list, &bdi->work_list);
	spin_unlock(&bdi->wb_lock);

	/*
	 * If the default thread isn't there, make sure we add it. When
	 * it gets created and wakes up, we'll run this work.
	 */
	if (unlikely(list_empty_careful(&bdi->wb_list)))
		wake_up_process(default_backing_dev_info.wb.task);
	else {
		struct bdi_writeback *wb = &bdi->wb;

		if (wb->task)
			wake_up_process(wb->task);
	}
}

static void
__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
		bool range_cyclic, bool for_background)
{
	struct wb_writeback_work *work;

	/*
	 * This is WB_SYNC_NONE writeback, so if allocation fails just
	 * wakeup the thread for old dirty data writeback
	 */
	work = kzalloc(sizeof(*work), GFP_ATOMIC);
	if (!work) {
		if (bdi->wb.task)
			wake_up_process(bdi->wb.task);
		return;
	}

	work->sync_mode	= WB_SYNC_NONE;
	work->nr_pages	= nr_pages;
	work->range_cyclic = range_cyclic;
	work->for_background = for_background;

	bdi_queue_work(bdi, work);
}

/**
 * bdi_start_writeback - start writeback
 * @bdi: the backing device to write from
 * @nr_pages: the number of pages to write
 *
 * Description:
 *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
 *   started when this function returns, we make no guarentees on
 *   completion. Caller need not hold sb s_umount semaphore.
 *
 */
void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
{
	__bdi_start_writeback(bdi, nr_pages, true, false);
}

/**
 * bdi_start_background_writeback - start background writeback
 * @bdi: the backing device to write from
 *
 * Description:
 *   This does WB_SYNC_NONE background writeback. The IO is only
 *   started when this function returns, we make no guarentees on
 *   completion. Caller need not hold sb s_umount semaphore.
 */
void bdi_start_background_writeback(struct backing_dev_info *bdi)
{
	__bdi_start_writeback(bdi, LONG_MAX, true, true);
}

/*
 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 * furthest end of its superblock's dirty-inode list.
 *
 * Before stamping the inode's ->dirtied_when, we check to see whether it is
 * already the most-recently-dirtied inode on the b_dirty list.  If that is
 * the case then the inode must have been redirtied while it was being written
 * out and we don't reset its dirtied_when.
 */
static void redirty_tail(struct inode *inode)
{
	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

	if (!list_empty(&wb->b_dirty)) {
		struct inode