page-writeback.c 38.4 KB
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/*
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 * mm/page-writeback.c
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 *
 * Copyright (C) 2002, Linus Torvalds.
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 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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 *
 * Contains functions related to writing back dirty pages at the
 * address_space level.
 *
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 * 10Apr2002	Andrew Morton
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 *		Initial version
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/init.h>
#include <linux/backing-dev.h>
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#include <linux/task_io_accounting_ops.h>
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#include <linux/blkdev.h>
#include <linux/mpage.h>
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#include <linux/rmap.h>
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#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
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#include <linux/buffer_head.h>
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#include <linux/pagevec.h>
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#include <trace/events/writeback.h>
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/*
 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
 * will look to see if it needs to force writeback or throttling.
 */
static long ratelimit_pages = 32;

/*
 * When balance_dirty_pages decides that the caller needs to perform some
 * non-background writeback, this is how many pages it will attempt to write.
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 * It should be somewhat larger than dirtied pages to ensure that reasonably
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 * large amounts of I/O are submitted.
 */
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static inline long sync_writeback_pages(unsigned long dirtied)
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{
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	if (dirtied < ratelimit_pages)
		dirtied = ratelimit_pages;

	return dirtied + dirtied / 2;
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}

/* The following parameters are exported via /proc/sys/vm */

/*
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 * Start background writeback (via writeback threads) at this percentage
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 */
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int dirty_background_ratio = 10;
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/*
 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
 * dirty_background_ratio * the amount of dirtyable memory
 */
unsigned long dirty_background_bytes;

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/*
 * free highmem will not be subtracted from the total free memory
 * for calculating free ratios if vm_highmem_is_dirtyable is true
 */
int vm_highmem_is_dirtyable;

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/*
 * The generator of dirty data starts writeback at this percentage
 */
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int vm_dirty_ratio = 20;
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/*
 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
 * vm_dirty_ratio * the amount of dirtyable memory
 */
unsigned long vm_dirty_bytes;

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/*
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 * The interval between `kupdate'-style writebacks
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 */
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unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
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/*
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 * The longest time for which data is allowed to remain dirty
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 */
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unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
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/*
 * Flag that makes the machine dump writes/reads and block dirtyings.
 */
int block_dump;

/*
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 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 * a full sync is triggered after this time elapses without any disk activity.
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 */
int laptop_mode;

EXPORT_SYMBOL(laptop_mode);

/* End of sysctl-exported parameters */


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/*
 * Scale the writeback cache size proportional to the relative writeout speeds.
 *
 * We do this by keeping a floating proportion between BDIs, based on page
 * writeback completions [end_page_writeback()]. Those devices that write out
 * pages fastest will get the larger share, while the slower will get a smaller
 * share.
 *
 * We use page writeout completions because we are interested in getting rid of
 * dirty pages. Having them written out is the primary goal.
 *
 * We introduce a concept of time, a period over which we measure these events,
 * because demand can/will vary over time. The length of this period itself is
 * measured in page writeback completions.
 *
 */
static struct prop_descriptor vm_completions;
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static struct prop_descriptor vm_dirties;
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/*
 * couple the period to the dirty_ratio:
 *
 *   period/2 ~ roundup_pow_of_two(dirty limit)
 */
static int calc_period_shift(void)
{
	unsigned long dirty_total;

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	if (vm_dirty_bytes)
		dirty_total = vm_dirty_bytes / PAGE_SIZE;
	else
		dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
				100;
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	return 2 + ilog2(dirty_total - 1);
}

/*
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 * update the period when the dirty threshold changes.
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 */
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static void update_completion_period(void)
{
	int shift = calc_period_shift();
	prop_change_shift(&vm_completions, shift);
	prop_change_shift(&vm_dirties, shift);
}

int dirty_background_ratio_handler(struct ctl_table *table, int write,
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		void __user *buffer, size_t *lenp,
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		loff_t *ppos)
{
	int ret;

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	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
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	if (ret == 0 && write)
		dirty_background_bytes = 0;
	return ret;
}

int dirty_background_bytes_handler(struct ctl_table *table, int write,
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		void __user *buffer, size_t *lenp,
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		loff_t *ppos)
{
	int ret;

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	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
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	if (ret == 0 && write)
		dirty_background_ratio = 0;
	return ret;
}

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int dirty_ratio_handler(struct ctl_table *table, int write,
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		void __user *buffer, size_t *lenp,
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		loff_t *ppos)
{
	int old_ratio = vm_dirty_ratio;
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	int ret;

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	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
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	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
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		update_completion_period();
		vm_dirty_bytes = 0;
	}
	return ret;
}


int dirty_bytes_handler(struct ctl_table *table, int write,
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		void __user *buffer, size_t *lenp,
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		loff_t *ppos)
{
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	unsigned long old_bytes = vm_dirty_bytes;
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	int ret;

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	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
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	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
		update_completion_period();
		vm_dirty_ratio = 0;
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	}
	return ret;
}

/*
 * Increment the BDI's writeout completion count and the global writeout
 * completion count. Called from test_clear_page_writeback().
 */
static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
{
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	__prop_inc_percpu_max(&vm_completions, &bdi->completions,
			      bdi->max_prop_frac);
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}

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void bdi_writeout_inc(struct backing_dev_info *bdi)
{
	unsigned long flags;

	local_irq_save(flags);
	__bdi_writeout_inc(bdi);
	local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(bdi_writeout_inc);

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void task_dirty_inc(struct task_struct *tsk)
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{
	prop_inc_single(&vm_dirties, &tsk->dirties);
}

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/*
 * Obtain an accurate fraction of the BDI's portion.
 */
static void bdi_writeout_fraction(struct backing_dev_info *bdi,
		long *numerator, long *denominator)
{
	if (bdi_cap_writeback_dirty(bdi)) {
		prop_fraction_percpu(&vm_completions, &bdi->completions,
				numerator, denominator);
	} else {
		*numerator = 0;
		*denominator = 1;
	}
}

/*
 * Clip the earned share of dirty pages to that which is actually available.
 * This avoids exceeding the total dirty_limit when the floating averages
 * fluctuate too quickly.
 */
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static void clip_bdi_dirty_limit(struct backing_dev_info *bdi,
		unsigned long dirty, unsigned long *pbdi_dirty)
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{
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	unsigned long avail_dirty;
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	avail_dirty = global_page_state(NR_FILE_DIRTY) +
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		 global_page_state(NR_WRITEBACK) +
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		 global_page_state(NR_UNSTABLE_NFS) +
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		 global_page_state(NR_WRITEBACK_TEMP);
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	if (avail_dirty < dirty)
		avail_dirty = dirty - avail_dirty;
	else
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		avail_dirty = 0;

	avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
		bdi_stat(bdi, BDI_WRITEBACK);

	*pbdi_dirty = min(*pbdi_dirty, avail_dirty);
}

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static inline void task_dirties_fraction(struct task_struct *tsk,
		long *numerator, long *denominator)
{
	prop_fraction_single(&vm_dirties, &tsk->dirties,
				numerator, denominator);
}

/*
 * scale the dirty limit
 *
 * task specific dirty limit:
 *
 *   dirty -= (dirty/8) * p_{t}
 */
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static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty)
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{
	long numerator, denominator;
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	unsigned long dirty = *pdirty;
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	u64 inv = dirty >> 3;

	task_dirties_fraction(tsk, &numerator, &denominator);
	inv *= numerator;
	do_div(inv, denominator);

	dirty -= inv;
	if (dirty < *pdirty/2)
		dirty = *pdirty/2;

	*pdirty = dirty;
}

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/*
 *
 */
static unsigned int bdi_min_ratio;

int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
{
	int ret = 0;

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	spin_lock_bh(&bdi_lock);
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	if (min_ratio > bdi->max_ratio) {
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		ret = -EINVAL;
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	} else {
		min_ratio -= bdi->min_ratio;
		if (bdi_min_ratio + min_ratio < 100) {
			bdi_min_ratio += min_ratio;
			bdi->min_ratio += min_ratio;
		} else {
			ret = -EINVAL;
		}
	}
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	spin_unlock_bh(&bdi_lock);
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	return ret;
}

int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
{
	int ret = 0;

	if (max_ratio > 100)
		return -EINVAL;

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	spin_lock_bh(&bdi_lock);
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	if (bdi->min_ratio > max_ratio) {
		ret = -EINVAL;
	} else {
		bdi->max_ratio = max_ratio;
		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
	}
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	spin_unlock_bh(&bdi_lock);
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	return ret;
}
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EXPORT_SYMBOL(bdi_set_max_ratio);
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/*
 * Work out the current dirty-memory clamping and background writeout
 * thresholds.
 *
 * The main aim here is to lower them aggressively if there is a lot of mapped
 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 * pages.  It is better to clamp down on writers than to start swapping, and
 * performing lots of scanning.
 *
 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 *
 * We don't permit the clamping level to fall below 5% - that is getting rather
 * excessive.
 *
 * We make sure that the background writeout level is below the adjusted
 * clamping level.
 */
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static unsigned long highmem_dirtyable_memory(unsigned long total)
{
#ifdef CONFIG_HIGHMEM
	int node;
	unsigned long x = 0;

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	for_each_node_state(node, N_HIGH_MEMORY) {
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		struct zone *z =
			&NODE_DATA(node)->node_zones[ZONE_HIGHMEM];

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		x += zone_page_state(z, NR_FREE_PAGES) +
		     zone_reclaimable_pages(z);
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	}
	/*
	 * Make sure that the number of highmem pages is never larger
	 * than the number of the total dirtyable memory. This can only
	 * occur in very strange VM situations but we want to make sure
	 * that this does not occur.
	 */
	return min(x, total);
#else
	return 0;
#endif
}

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/**
 * determine_dirtyable_memory - amount of memory that may be used
 *
 * Returns the numebr of pages that can currently be freed and used
 * by the kernel for direct mappings.
 */
unsigned long determine_dirtyable_memory(void)
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{
	unsigned long x;

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	x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
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	if (!vm_highmem_is_dirtyable)
		x -= highmem_dirtyable_memory(x);

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	return x + 1;	/* Ensure that we never return 0 */
}

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void
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get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
		 unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
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{
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	unsigned long background;
	unsigned long dirty;
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	unsigned long available_memory = determine_dirtyable_memory();
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	struct task_struct *tsk;

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	if (vm_dirty_bytes)
		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
	else {
		int dirty_ratio;

		dirty_ratio = vm_dirty_ratio;
		if (dirty_ratio < 5)
			dirty_ratio = 5;
		dirty = (dirty_ratio * available_memory) / 100;
	}
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	if (dirty_background_bytes)
		background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
	else
		background = (dirty_background_ratio * available_memory) / 100;
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	if (background >= dirty)
		background = dirty / 2;
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	tsk = current;
	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
		background += background / 4;
		dirty += dirty / 4;
	}
	*pbackground = background;
	*pdirty = dirty;
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	if (bdi) {
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		u64 bdi_dirty;
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		long numerator, denominator;

		/*
		 * Calculate this BDI's share of the dirty ratio.
		 */
		bdi_writeout_fraction(bdi, &numerator, &denominator);

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		bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
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		bdi_dirty *= numerator;
		do_div(bdi_dirty, denominator);
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		bdi_dirty += (dirty * bdi->min_ratio) / 100;
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		if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
			bdi_dirty = dirty * bdi->max_ratio / 100;
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		*pbdi_dirty = bdi_dirty;
		clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
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		task_dirty_limit(current, pbdi_dirty);
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	}
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}

/*
 * balance_dirty_pages() must be called by processes which are generating dirty
 * data.  It looks at the number of dirty pages in the machine and will force
 * the caller to perform writeback if the system is over `vm_dirty_ratio'.
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 * If we're over `background_thresh' then the writeback threads are woken to
 * perform some writeout.
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 */
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static void balance_dirty_pages(struct address_space *mapping,
				unsigned long write_chunk)
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{
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	long nr_reclaimable, bdi_nr_reclaimable;
	long nr_writeback, bdi_nr_writeback;
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	unsigned long background_thresh;
	unsigned long dirty_thresh;
	unsigned long bdi_thresh;
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	unsigned long pages_written = 0;
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	unsigned long pause = 1;
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	struct backing_dev_info *bdi = mapping->backing_dev_info;

	for (;;) {
		struct writeback_control wbc = {
			.sync_mode	= WB_SYNC_NONE,
			.older_than_this = NULL,
			.nr_to_write	= write_chunk,
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			.range_cyclic	= 1,
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		};

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		get_dirty_limits(&background_thresh, &dirty_thresh,
				&bdi_thresh, bdi);
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		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
					global_page_state(NR_UNSTABLE_NFS);
		nr_writeback = global_page_state(NR_WRITEBACK);

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		bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
		bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
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		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;
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		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the bdi limits are ramping up.
		 */
		if (nr_reclaimable + nr_writeback <
				(background_thresh + dirty_thresh) / 2)
			break;

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		if (!bdi->dirty_exceeded)
			bdi->dirty_exceeded = 1;
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		/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
		 * Unstable writes are a feature of certain networked
		 * filesystems (i.e. NFS) in which data may have been
		 * written to the server's write cache, but has not yet
		 * been flushed to permanent storage.
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		 * Only move pages to writeback if this bdi is over its
		 * threshold otherwise wait until the disk writes catch
		 * up.
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		 */
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		trace_wbc_balance_dirty_start(&wbc, bdi);
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		if (bdi_nr_reclaimable > bdi_thresh) {
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			writeback_inodes_wb(&bdi->wb, &wbc);
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			pages_written += write_chunk - wbc.nr_to_write;
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			get_dirty_limits(&background_thresh, &dirty_thresh,
				       &bdi_thresh, bdi);
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			trace_wbc_balance_dirty_written(&wbc, bdi);
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		}

		/*
		 * In order to avoid the stacked BDI deadlock we need
		 * to ensure we accurately count the 'dirty' pages when
		 * the threshold is low.
		 *
		 * Otherwise it would be possible to get thresh+n pages
		 * reported dirty, even though there are thresh-m pages
		 * actually dirty; with m+n sitting in the percpu
		 * deltas.
		 */
		if (bdi_thresh < 2*bdi_stat_error(bdi)) {
			bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
		} else if (bdi_nr_reclaimable) {
			bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
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		}
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		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;
		if (pages_written >= write_chunk)
			break;		/* We've done our duty */

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		trace_wbc_balance_dirty_wait(&wbc, bdi);
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		__set_current_state(TASK_INTERRUPTIBLE);
		io_schedule_timeout(pause);
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		/*
		 * Increase the delay for each loop, up to our previous
		 * default of taking a 100ms nap.
		 */
		pause <<= 1;
		if (pause > HZ / 10)
			pause = HZ / 10;
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	}

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	if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
			bdi->dirty_exceeded)
		bdi->dirty_exceeded = 0;
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	if (writeback_in_progress(bdi))
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		return;
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	/*
	 * In laptop mode, we wait until hitting the higher threshold before
	 * starting background writeout, and then write out all the way down
	 * to the lower threshold.  So slow writers cause minimal disk activity.
	 *
	 * In normal mode, we start background writeout at the lower
	 * background_thresh, to keep the amount of dirty memory low.
	 */
	if ((laptop_mode && pages_written) ||
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	    (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
			       + global_page_state(NR_UNSTABLE_NFS))
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					  > background_thresh)))
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		bdi_start_background_writeback(bdi);
L
Linus Torvalds 已提交
604 605
}

606
void set_page_dirty_balance(struct page *page, int page_mkwrite)
P
Peter Zijlstra 已提交
607
{
608
	if (set_page_dirty(page) || page_mkwrite) {
P
Peter Zijlstra 已提交
609 610 611 612 613 614 615
		struct address_space *mapping = page_mapping(page);

		if (mapping)
			balance_dirty_pages_ratelimited(mapping);
	}
}

616 617
static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;

L
Linus Torvalds 已提交
618
/**
619
 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
620
 * @mapping: address_space which was dirtied
621
 * @nr_pages_dirtied: number of pages which the caller has just dirtied
L
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622 623 624 625 626 627 628 629 630 631
 *
 * Processes which are dirtying memory should call in here once for each page
 * which was newly dirtied.  The function will periodically check the system's
 * dirty state and will initiate writeback if needed.
 *
 * On really big machines, get_writeback_state is expensive, so try to avoid
 * calling it too often (ratelimiting).  But once we're over the dirty memory
 * limit we decrease the ratelimiting by a lot, to prevent individual processes
 * from overshooting the limit by (ratelimit_pages) each.
 */
632 633
void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
					unsigned long nr_pages_dirtied)
L
Linus Torvalds 已提交
634
{
635 636
	unsigned long ratelimit;
	unsigned long *p;
L
Linus Torvalds 已提交
637 638

	ratelimit = ratelimit_pages;
P
Peter Zijlstra 已提交
639
	if (mapping->backing_dev_info->dirty_exceeded)
L
Linus Torvalds 已提交
640 641 642 643 644 645
		ratelimit = 8;

	/*
	 * Check the rate limiting. Also, we do not want to throttle real-time
	 * tasks in balance_dirty_pages(). Period.
	 */
646
	preempt_disable();
647
	p =  &__get_cpu_var(bdp_ratelimits);
648 649
	*p += nr_pages_dirtied;
	if (unlikely(*p >= ratelimit)) {
650
		ratelimit = sync_writeback_pages(*p);
651 652
		*p = 0;
		preempt_enable();
653
		balance_dirty_pages(mapping, ratelimit);
L
Linus Torvalds 已提交
654 655
		return;
	}
656
	preempt_enable();
L
Linus Torvalds 已提交
657
}
658
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
L
Linus Torvalds 已提交
659

660
void throttle_vm_writeout(gfp_t gfp_mask)
L
Linus Torvalds 已提交
661
{
662 663
	unsigned long background_thresh;
	unsigned long dirty_thresh;
L
Linus Torvalds 已提交
664 665

        for ( ; ; ) {
P
Peter Zijlstra 已提交
666
		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
L
Linus Torvalds 已提交
667 668 669 670 671 672 673

                /*
                 * Boost the allowable dirty threshold a bit for page
                 * allocators so they don't get DoS'ed by heavy writers
                 */
                dirty_thresh += dirty_thresh / 10;      /* wheeee... */

674 675 676
                if (global_page_state(NR_UNSTABLE_NFS) +
			global_page_state(NR_WRITEBACK) <= dirty_thresh)
                        	break;
677
                congestion_wait(BLK_RW_ASYNC, HZ/10);
678 679 680 681 682 683 684 685

		/*
		 * The caller might hold locks which can prevent IO completion
		 * or progress in the filesystem.  So we cannot just sit here
		 * waiting for IO to complete.
		 */
		if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
			break;
L
Linus Torvalds 已提交
686 687 688 689 690 691 692
        }
}

/*
 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 */
int dirty_writeback_centisecs_handler(ctl_table *table, int write,
693
	void __user *buffer, size_t *length, loff_t *ppos)
L
Linus Torvalds 已提交
694
{
695
	proc_dointvec(table, write, buffer, length, ppos);
696
	bdi_arm_supers_timer();
L
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697 698 699
	return 0;
}

700
#ifdef CONFIG_BLOCK
701
void laptop_mode_timer_fn(unsigned long data)
L
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702
{
703 704 705
	struct request_queue *q = (struct request_queue *)data;
	int nr_pages = global_page_state(NR_FILE_DIRTY) +
		global_page_state(NR_UNSTABLE_NFS);
L
Linus Torvalds 已提交
706

707 708 709 710 711
	/*
	 * We want to write everything out, not just down to the dirty
	 * threshold
	 */
	if (bdi_has_dirty_io(&q->backing_dev_info))
712
		bdi_start_writeback(&q->backing_dev_info, nr_pages);
L
Linus Torvalds 已提交
713 714 715 716 717 718 719
}

/*
 * We've spun up the disk and we're in laptop mode: schedule writeback
 * of all dirty data a few seconds from now.  If the flush is already scheduled
 * then push it back - the user is still using the disk.
 */
720
void laptop_io_completion(struct backing_dev_info *info)
L
Linus Torvalds 已提交
721
{
722
	mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
L
Linus Torvalds 已提交
723 724 725 726 727 728 729 730 731
}

/*
 * We're in laptop mode and we've just synced. The sync's writes will have
 * caused another writeback to be scheduled by laptop_io_completion.
 * Nothing needs to be written back anymore, so we unschedule the writeback.
 */
void laptop_sync_completion(void)
{
732 733 734 735 736 737 738 739
	struct backing_dev_info *bdi;

	rcu_read_lock();

	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
		del_timer(&bdi->laptop_mode_wb_timer);

	rcu_read_unlock();
L
Linus Torvalds 已提交
740
}
741
#endif
L
Linus Torvalds 已提交
742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759

/*
 * If ratelimit_pages is too high then we can get into dirty-data overload
 * if a large number of processes all perform writes at the same time.
 * If it is too low then SMP machines will call the (expensive)
 * get_writeback_state too often.
 *
 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 * thresholds before writeback cuts in.
 *
 * But the limit should not be set too high.  Because it also controls the
 * amount of memory which the balance_dirty_pages() caller has to write back.
 * If this is too large then the caller will block on the IO queue all the
 * time.  So limit it to four megabytes - the balance_dirty_pages() caller
 * will write six megabyte chunks, max.
 */

760
void writeback_set_ratelimit(void)
L
Linus Torvalds 已提交
761
{
762
	ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
L
Linus Torvalds 已提交
763 764 765 766 767 768
	if (ratelimit_pages < 16)
		ratelimit_pages = 16;
	if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
		ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
}

769
static int __cpuinit
L
Linus Torvalds 已提交
770 771
ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
{
772
	writeback_set_ratelimit();
773
	return NOTIFY_DONE;
L
Linus Torvalds 已提交
774 775
}

776
static struct notifier_block __cpuinitdata ratelimit_nb = {
L
Linus Torvalds 已提交
777 778 779 780 781
	.notifier_call	= ratelimit_handler,
	.next		= NULL,
};

/*
782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797
 * Called early on to tune the page writeback dirty limits.
 *
 * We used to scale dirty pages according to how total memory
 * related to pages that could be allocated for buffers (by
 * comparing nr_free_buffer_pages() to vm_total_pages.
 *
 * However, that was when we used "dirty_ratio" to scale with
 * all memory, and we don't do that any more. "dirty_ratio"
 * is now applied to total non-HIGHPAGE memory (by subtracting
 * totalhigh_pages from vm_total_pages), and as such we can't
 * get into the old insane situation any more where we had
 * large amounts of dirty pages compared to a small amount of
 * non-HIGHMEM memory.
 *
 * But we might still want to scale the dirty_ratio by how
 * much memory the box has..
L
Linus Torvalds 已提交
798 799 800
 */
void __init page_writeback_init(void)
{
P
Peter Zijlstra 已提交
801 802
	int shift;

803
	writeback_set_ratelimit();
L
Linus Torvalds 已提交
804
	register_cpu_notifier(&ratelimit_nb);
P
Peter Zijlstra 已提交
805 806 807

	shift = calc_period_shift();
	prop_descriptor_init(&vm_completions, shift);
P
Peter Zijlstra 已提交
808
	prop_descriptor_init(&vm_dirties, shift);
L
Linus Torvalds 已提交
809 810
}

811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830
/**
 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
 * @mapping: address space structure to write
 * @start: starting page index
 * @end: ending page index (inclusive)
 *
 * This function scans the page range from @start to @end (inclusive) and tags
 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
 * that write_cache_pages (or whoever calls this function) will then use
 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
 * used to avoid livelocking of writeback by a process steadily creating new
 * dirty pages in the file (thus it is important for this function to be quick
 * so that it can tag pages faster than a dirtying process can create them).
 */
/*
 * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
 */
void tag_pages_for_writeback(struct address_space *mapping,
			     pgoff_t start, pgoff_t end)
{
R
Randy Dunlap 已提交
831
#define WRITEBACK_TAG_BATCH 4096
832 833 834 835 836 837 838 839 840 841 842 843 844 845
	unsigned long tagged;

	do {
		spin_lock_irq(&mapping->tree_lock);
		tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
				&start, end, WRITEBACK_TAG_BATCH,
				PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
		spin_unlock_irq(&mapping->tree_lock);
		WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
		cond_resched();
	} while (tagged >= WRITEBACK_TAG_BATCH);
}
EXPORT_SYMBOL(tag_pages_for_writeback);

846
/**
847
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
848 849
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
850 851
 * @writepage: function called for each page
 * @data: data passed to writepage function
852
 *
853
 * If a page is already under I/O, write_cache_pages() skips it, even
854 855 856 857 858 859
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
860 861 862 863 864 865 866
 *
 * To avoid livelocks (when other process dirties new pages), we first tag
 * pages which should be written back with TOWRITE tag and only then start
 * writing them. For data-integrity sync we have to be careful so that we do
 * not miss some pages (e.g., because some other process has cleared TOWRITE
 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
 * by the process clearing the DIRTY tag (and submitting the page for IO).
867
 */
868 869 870
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
871 872 873 874 875
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
N
Nick Piggin 已提交
876
	pgoff_t uninitialized_var(writeback_index);
877 878
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
879
	pgoff_t done_index;
N
Nick Piggin 已提交
880
	int cycled;
881
	int range_whole = 0;
882
	int tag;
883 884 885

	pagevec_init(&pvec, 0);
	if (wbc->range_cyclic) {
N
Nick Piggin 已提交
886 887 888 889 890 891
		writeback_index = mapping->writeback_index; /* prev offset */
		index = writeback_index;
		if (index == 0)
			cycled = 1;
		else
			cycled = 0;
892 893 894 895 896 897
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
N
Nick Piggin 已提交
898
		cycled = 1; /* ignore range_cyclic tests */
899
	}
900 901 902 903
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;
904
retry:
905 906
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);
907
	done_index = index;
N
Nick Piggin 已提交
908 909 910
	while (!done && (index <= end)) {
		int i;

911
		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
N
Nick Piggin 已提交
912 913 914
			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if (nr_pages == 0)
			break;
915 916 917 918 919

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			/*
920 921 922 923 924
			 * At this point, the page may be truncated or
			 * invalidated (changing page->mapping to NULL), or
			 * even swizzled back from swapper_space to tmpfs file
			 * mapping. However, page->index will not change
			 * because we have a reference on the page.
925
			 */
926 927 928 929 930 931 932 933 934 935 936
			if (page->index > end) {
				/*
				 * can't be range_cyclic (1st pass) because
				 * end == -1 in that case.
				 */
				done = 1;
				break;
			}

			done_index = page->index + 1;

937 938
			lock_page(page);

N
Nick Piggin 已提交
939 940 941 942 943 944 945 946
			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data interity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
947
			if (unlikely(page->mapping != mapping)) {
N
Nick Piggin 已提交
948
continue_unlock:
949 950 951 952
				unlock_page(page);
				continue;
			}

953 954 955 956 957 958 959 960 961 962 963
			if (!PageDirty(page)) {
				/* someone wrote it for us */
				goto continue_unlock;
			}

			if (PageWriteback(page)) {
				if (wbc->sync_mode != WB_SYNC_NONE)
					wait_on_page_writeback(page);
				else
					goto continue_unlock;
			}
964

965 966
			BUG_ON(PageWriteback(page));
			if (!clear_page_dirty_for_io(page))
N
Nick Piggin 已提交
967
				goto continue_unlock;
968

969
			trace_wbc_writepage(wbc, mapping->backing_dev_info);
970
			ret = (*writepage)(page, wbc, data);
971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987
			if (unlikely(ret)) {
				if (ret == AOP_WRITEPAGE_ACTIVATE) {
					unlock_page(page);
					ret = 0;
				} else {
					/*
					 * done_index is set past this page,
					 * so media errors will not choke
					 * background writeout for the entire
					 * file. This has consequences for
					 * range_cyclic semantics (ie. it may
					 * not be suitable for data integrity
					 * writeout).
					 */
					done = 1;
					break;
				}
988
			}
989

990 991
			if (wbc->nr_to_write > 0) {
				if (--wbc->nr_to_write == 0 &&
F
Federico Cuello 已提交
992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005
				    wbc->sync_mode == WB_SYNC_NONE) {
					/*
					 * We stop writing back only if we are
					 * not doing integrity sync. In case of
					 * integrity sync we have to keep going
					 * because someone may be concurrently
					 * dirtying pages, and we might have
					 * synced a lot of newly appeared dirty
					 * pages, but have not synced all of the
					 * old dirty pages.
					 */
					done = 1;
					break;
				}
1006
			}
1007 1008 1009 1010
		}
		pagevec_release(&pvec);
		cond_resched();
	}
1011
	if (!cycled && !done) {
1012
		/*
N
Nick Piggin 已提交
1013
		 * range_cyclic:
1014 1015 1016
		 * We hit the last page and there is more work to be done: wrap
		 * back to the start of the file
		 */
N
Nick Piggin 已提交
1017
		cycled = 1;
1018
		index = 0;
N
Nick Piggin 已提交
1019
		end = writeback_index - 1;
1020 1021
		goto retry;
	}
1022 1023
	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
		mapping->writeback_index = done_index;
1024

1025 1026
	return ret;
}
1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058
EXPORT_SYMBOL(write_cache_pages);

/*
 * Function used by generic_writepages to call the real writepage
 * function and set the mapping flags on error
 */
static int __writepage(struct page *page, struct writeback_control *wbc,
		       void *data)
{
	struct address_space *mapping = data;
	int ret = mapping->a_ops->writepage(page, wbc);
	mapping_set_error(mapping, ret);
	return ret;
}

/**
 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 *
 * This is a library function, which implements the writepages()
 * address_space_operation.
 */
int generic_writepages(struct address_space *mapping,
		       struct writeback_control *wbc)
{
	/* deal with chardevs and other special file */
	if (!mapping->a_ops->writepage)
		return 0;

	return write_cache_pages(mapping, wbc, __writepage, mapping);
}
1059 1060 1061

EXPORT_SYMBOL(generic_writepages);

L
Linus Torvalds 已提交
1062 1063
int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
1064 1065
	int ret;

L
Linus Torvalds 已提交
1066 1067 1068
	if (wbc->nr_to_write <= 0)
		return 0;
	if (mapping->a_ops->writepages)
1069
		ret = mapping->a_ops->writepages(mapping, wbc);
1070 1071 1072
	else
		ret = generic_writepages(mapping, wbc);
	return ret;
L
Linus Torvalds 已提交
1073 1074 1075 1076
}

/**
 * write_one_page - write out a single page and optionally wait on I/O
1077 1078
 * @page: the page to write
 * @wait: if true, wait on writeout
L
Linus Torvalds 已提交
1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113
 *
 * The page must be locked by the caller and will be unlocked upon return.
 *
 * write_one_page() returns a negative error code if I/O failed.
 */
int write_one_page(struct page *page, int wait)
{
	struct address_space *mapping = page->mapping;
	int ret = 0;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_ALL,
		.nr_to_write = 1,
	};

	BUG_ON(!PageLocked(page));

	if (wait)
		wait_on_page_writeback(page);

	if (clear_page_dirty_for_io(page)) {
		page_cache_get(page);
		ret = mapping->a_ops->writepage(page, &wbc);
		if (ret == 0 && wait) {
			wait_on_page_writeback(page);
			if (PageError(page))
				ret = -EIO;
		}
		page_cache_release(page);
	} else {
		unlock_page(page);
	}
	return ret;
}
EXPORT_SYMBOL(write_one_page);

1114 1115 1116 1117 1118 1119 1120 1121 1122 1123
/*
 * For address_spaces which do not use buffers nor write back.
 */
int __set_page_dirty_no_writeback(struct page *page)
{
	if (!PageDirty(page))
		SetPageDirty(page);
	return 0;
}

1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137
/*
 * Helper function for set_page_dirty family.
 * NOTE: This relies on being atomic wrt interrupts.
 */
void account_page_dirtied(struct page *page, struct address_space *mapping)
{
	if (mapping_cap_account_dirty(mapping)) {
		__inc_zone_page_state(page, NR_FILE_DIRTY);
		__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
		task_dirty_inc(current);
		task_io_account_write(PAGE_CACHE_SIZE);
	}
}

L
Linus Torvalds 已提交
1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150
/*
 * For address_spaces which do not use buffers.  Just tag the page as dirty in
 * its radix tree.
 *
 * This is also used when a single buffer is being dirtied: we want to set the
 * page dirty in that case, but not all the buffers.  This is a "bottom-up"
 * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
 *
 * Most callers have locked the page, which pins the address_space in memory.
 * But zap_pte_range() does not lock the page, however in that case the
 * mapping is pinned by the vma's ->vm_file reference.
 *
 * We take care to handle the case where the page was truncated from the
S
Simon Arlott 已提交
1151
 * mapping by re-checking page_mapping() inside tree_lock.
L
Linus Torvalds 已提交
1152 1153 1154 1155 1156 1157 1158
 */
int __set_page_dirty_nobuffers(struct page *page)
{
	if (!TestSetPageDirty(page)) {
		struct address_space *mapping = page_mapping(page);
		struct address_space *mapping2;

1159 1160 1161
		if (!mapping)
			return 1;

N
Nick Piggin 已提交
1162
		spin_lock_irq(&mapping->tree_lock);
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		mapping2 = page_mapping(page);
		if (mapping2) { /* Race with truncate? */
			BUG_ON(mapping2 != mapping);
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			WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
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			account_page_dirtied(page, mapping);
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			radix_tree_tag_set(&mapping->page_tree,
				page_index(page), PAGECACHE_TAG_DIRTY);
		}
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		spin_unlock_irq(&mapping->tree_lock);
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		if (mapping->host) {
			/* !PageAnon && !swapper_space */
			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
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		}
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		return 1;
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	}
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	return 0;
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}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);

/*
 * When a writepage implementation decides that it doesn't want to write this
 * page for some reason, it should redirty the locked page via
 * redirty_page_for_writepage() and it should then unlock the page and return 0
 */
int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
{
	wbc->pages_skipped++;
	return __set_page_dirty_nobuffers(page);
}
EXPORT_SYMBOL(redirty_page_for_writepage);

/*
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 * Dirty a page.
 *
 * For pages with a mapping this should be done under the page lock
 * for the benefit of asynchronous memory errors who prefer a consistent
 * dirty state. This rule can be broken in some special cases,
 * but should be better not to.
 *
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 * If the mapping doesn't provide a set_page_dirty a_op, then
 * just fall through and assume that it wants buffer_heads.
 */
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int set_page_dirty(struct page *page)
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{
	struct address_space *mapping = page_mapping(page);

	if (likely(mapping)) {
		int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
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#ifdef CONFIG_BLOCK
		if (!spd)
			spd = __set_page_dirty_buffers;
#endif
		return (*spd)(page);
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	}
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	if (!PageDirty(page)) {
		if (!TestSetPageDirty(page))
			return 1;
	}
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	return 0;
}
EXPORT_SYMBOL(set_page_dirty);

/*
 * set_page_dirty() is racy if the caller has no reference against
 * page->mapping->host, and if the page is unlocked.  This is because another
 * CPU could truncate the page off the mapping and then free the mapping.
 *
 * Usually, the page _is_ locked, or the caller is a user-space process which
 * holds a reference on the inode by having an open file.
 *
 * In other cases, the page should be locked before running set_page_dirty().
 */
int set_page_dirty_lock(struct page *page)
{
	int ret;

1239
	lock_page_nosync(page);
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	ret = set_page_dirty(page);
	unlock_page(page);
	return ret;
}
EXPORT_SYMBOL(set_page_dirty_lock);

/*
 * Clear a page's dirty flag, while caring for dirty memory accounting.
 * Returns true if the page was previously dirty.
 *
 * This is for preparing to put the page under writeout.  We leave the page
 * tagged as dirty in the radix tree so that a concurrent write-for-sync
 * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
 * implementation will run either set_page_writeback() or set_page_dirty(),
 * at which stage we bring the page's dirty flag and radix-tree dirty tag
 * back into sync.
 *
 * This incoherency between the page's dirty flag and radix-tree tag is
 * unfortunate, but it only exists while the page is locked.
 */
int clear_page_dirty_for_io(struct page *page)
{
	struct address_space *mapping = page_mapping(page);

1264 1265
	BUG_ON(!PageLocked(page));

1266
	ClearPageReclaim(page);
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	if (mapping && mapping_cap_account_dirty(mapping)) {
		/*
		 * Yes, Virginia, this is indeed insane.
		 *
		 * We use this sequence to make sure that
		 *  (a) we account for dirty stats properly
		 *  (b) we tell the low-level filesystem to
		 *      mark the whole page dirty if it was
		 *      dirty in a pagetable. Only to then
		 *  (c) clean the page again and return 1 to
		 *      cause the writeback.
		 *
		 * This way we avoid all nasty races with the
		 * dirty bit in multiple places and clearing
		 * them concurrently from different threads.
		 *
		 * Note! Normally the "set_page_dirty(page)"
		 * has no effect on the actual dirty bit - since
		 * that will already usually be set. But we
		 * need the side effects, and it can help us
		 * avoid races.
		 *
		 * We basically use the page "master dirty bit"
		 * as a serialization point for all the different
		 * threads doing their things.
		 */
		if (page_mkclean(page))
			set_page_dirty(page);
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		/*
		 * We carefully synchronise fault handlers against
		 * installing a dirty pte and marking the page dirty
		 * at this point. We do this by having them hold the
		 * page lock at some point after installing their
		 * pte, but before marking the page dirty.
		 * Pages are always locked coming in here, so we get
		 * the desired exclusion. See mm/memory.c:do_wp_page()
		 * for more comments.
		 */
1305
		if (TestClearPageDirty(page)) {
1306
			dec_zone_page_state(page, NR_FILE_DIRTY);
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			dec_bdi_stat(mapping->backing_dev_info,
					BDI_RECLAIMABLE);
1309
			return 1;
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		}
1311
		return 0;
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	}
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	return TestClearPageDirty(page);
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}
1315
EXPORT_SYMBOL(clear_page_dirty_for_io);
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int test_clear_page_writeback(struct page *page)
{
	struct address_space *mapping = page_mapping(page);
	int ret;

	if (mapping) {
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		struct backing_dev_info *bdi = mapping->backing_dev_info;
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		unsigned long flags;

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		spin_lock_irqsave(&mapping->tree_lock, flags);
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		ret = TestClearPageWriteback(page);
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		if (ret) {
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			radix_tree_tag_clear(&mapping->page_tree,
						page_index(page),
						PAGECACHE_TAG_WRITEBACK);
1332
			if (bdi_cap_account_writeback(bdi)) {
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				__dec_bdi_stat(bdi, BDI_WRITEBACK);
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				__bdi_writeout_inc(bdi);
			}
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		}
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		spin_unlock_irqrestore(&mapping->tree_lock, flags);
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	} else {
		ret = TestClearPageWriteback(page);
	}
1341 1342
	if (ret)
		dec_zone_page_state(page, NR_WRITEBACK);
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	return ret;
}

int test_set_page_writeback(struct page *page)
{
	struct address_space *mapping = page_mapping(page);
	int ret;

	if (mapping) {
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		struct backing_dev_info *bdi = mapping->backing_dev_info;
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		unsigned long flags;

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		spin_lock_irqsave(&mapping->tree_lock, flags);
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		ret = TestSetPageWriteback(page);
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		if (!ret) {
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			radix_tree_tag_set(&mapping->page_tree,
						page_index(page),
						PAGECACHE_TAG_WRITEBACK);
1361
			if (bdi_cap_account_writeback(bdi))
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				__inc_bdi_stat(bdi, BDI_WRITEBACK);
		}
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		if (!PageDirty(page))
			radix_tree_tag_clear(&mapping->page_tree,
						page_index(page),
						PAGECACHE_TAG_DIRTY);
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		radix_tree_tag_clear(&mapping->page_tree,
				     page_index(page),
				     PAGECACHE_TAG_TOWRITE);
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		spin_unlock_irqrestore(&mapping->tree_lock, flags);
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	} else {
		ret = TestSetPageWriteback(page);
	}
1375 1376
	if (!ret)
		inc_zone_page_state(page, NR_WRITEBACK);
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	return ret;

}
EXPORT_SYMBOL(test_set_page_writeback);

/*
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 * Return true if any of the pages in the mapping are marked with the
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 * passed tag.
 */
int mapping_tagged(struct address_space *mapping, int tag)
{
	int ret;
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	rcu_read_lock();
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	ret = radix_tree_tagged(&mapping->page_tree, tag);
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	rcu_read_unlock();
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	return ret;
}
EXPORT_SYMBOL(mapping_tagged);