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

#include <linux/kernel.h>
#include <linux/export.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>
#include <linux/task_io_accounting_ops.h>
#include <linux/blkdev.h>
#include <linux/mpage.h>
#include <linux/rmap.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
#include <trace/events/writeback.h>

/*
* Sleep at most 200ms at a time in balance_dirty_pages().
*/
#define MAX_PAUSE max(HZ/5, 1)

/*
* Estimate write bandwidth at 200ms intervals.
*/
#define BANDWIDTH_INTERVAL max(HZ/5, 1)

#define RATELIMIT_CALC_SHIFT 10

/*
* 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;

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

/*
* Start background writeback (via writeback threads) at this percentage
*/
int dirty_background_ratio = 10;

/*
* 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;

/*
* 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;

/*
* The generator of dirty data starts writeback at this percentage
*/
int vm_dirty_ratio = 20;

/*
* 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;

/*
* The interval between `kupdate'-style writebacks
*/
unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */

/*
* The longest time for which data is allowed to remain dirty
*/
unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */

/*
* Flag that makes the machine dump writes/reads and block dirtyings.
*/
int block_dump;

/*
* 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.
*/
int laptop_mode;

EXPORT_SYMBOL(laptop_mode);

/* End of sysctl-exported parameters */

unsigned long global_dirty_limit;

/*
* 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;

/*
* 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;

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

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

writeback_set_ratelimit();
}

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

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

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

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

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

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


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

ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
update_completion_period();
vm_dirty_ratio = 0;
}
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)
{
__inc_bdi_stat(bdi, BDI_WRITTEN);
__prop_inc_percpu_max(&vm_completions, &bdi->completions,
bdi->max_prop_frac);
}

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);

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

/*
* bdi_min_ratio keeps the sum of the minimum dirty shares of all
* registered backing devices, which, for obvious reasons, can not
* exceed 100%.
*/
static unsigned int bdi_min_ratio;

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

spin_lock_bh(&bdi_lock);
if (min_ratio > bdi->max_ratio) {
ret = -EINVAL;
} 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;
}
}
spin_unlock_bh(&bdi_lock);

return ret;
}

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

if (max_ratio > 100)
return -EINVAL;

spin_lock_bh(&bdi_lock);
if (bdi->min_ratio > max_ratio) {
ret = -EINVAL;
} else {
bdi->max_ratio = max_ratio;
bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
}
spin_unlock_bh(&bdi_lock);

return ret;
}
EXPORT_SYMBOL(bdi_set_max_ratio);

/*
* 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.
*/

static unsigned long highmem_dirtyable_memory(unsigned long total)
{
#ifdef CONFIG_HIGHMEM
int node;
unsigned long x = 0;

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

x += zone_page_state(z, NR_FREE_PAGES) +
zone_reclaimable_pages(z);
}
/*
* 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
}

/**
* 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)
{
unsigned long x;

x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();

if (!vm_highmem_is_dirtyable)
x -= highmem_dirtyable_memory(x);

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

static unsigned long dirty_freerun_ceiling(unsigned long thresh,
unsigned long bg_thresh)
{
return (thresh + bg_thresh) / 2;
}

static unsigned long hard_dirty_limit(unsigned long thresh)
{
return max(thresh, global_dirty_limit);
}

/*
* global_dirty_limits - background-writeback and dirty-throttling thresholds
*
* Calculate the dirty thresholds based on sysctl parameters
* - vm.dirty_background_ratio or vm.dirty_background_bytes
* - vm.dirty_ratio or vm.dirty_bytes
* The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
* real-time tasks.
*/
void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
{
unsigned long background;
unsigned long dirty;
unsigned long uninitialized_var(available_memory);
struct task_struct *tsk;

if (!vm_dirty_bytes || !dirty_background_bytes)
available_memory = determine_dirtyable_memory();

if (vm_dirty_bytes)
dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
else
dirty = (vm_dirty_ratio * available_memory) / 100;

if (dirty_background_bytes)
background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
else
background = (dirty_background_ratio * available_memory) / 100;

if (background >= dirty)
background = dirty / 2;
tsk = current;
if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
background += background / 4;
dirty += dirty / 4;
}
*pbackground = background;
*pdirty = dirty;
trace_global_dirty_state(background, dirty);
}

/**
* bdi_dirty_limit - @bdi's share of dirty throttling threshold
* @bdi: the backing_dev_info to query
* @dirty: global dirty limit in pages
*
* Returns @bdi's dirty limit in pages. The term "dirty" in the context of
* dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
*
* Note that balance_dirty_pages() will only seriously take it as a hard limit
* when sleeping max_pause per page is not enough to keep the dirty pages under
* control. For example, when the device is completely stalled due to some error
* conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
* In the other normal situations, it acts more gently by throttling the tasks
* more (rather than completely block them) when the bdi dirty pages go high.
*
* It allocates high/low dirty limits to fast/slow devices, in order to prevent
* - starving fast devices
* - piling up dirty pages (that will take long time to sync) on slow devices
*
* The bdi's share of dirty limit will be adapting to its throughput and
* bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
*/
unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
{
u64 bdi_dirty;
long numerator, denominator;

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

bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
bdi_dirty *= numerator;
do_div(bdi_dirty, denominator);

bdi_dirty += (dirty * bdi->min_ratio) / 100;
if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
bdi_dirty = dirty * bdi->max_ratio / 100;

return bdi_dirty;
}

/*
* Dirty position control.
*
* (o) global/bdi setpoints
*
* We want the dirty pages be balanced around the global/bdi setpoints.
* When the number of dirty pages is higher/lower than the setpoint, the
* dirty position control ratio (and hence task dirty ratelimit) will be
* decreased/increased to bring the dirty pages back to the setpoint.
*
* pos_ratio = 1 << RATELIMIT_CALC_SHIFT
*
* if (dirty < setpoint) scale up pos_ratio
* if (dirty > setpoint) scale down pos_ratio
*
* if (bdi_dirty < bdi_setpoint) scale up pos_ratio
* if (bdi_dirty > bdi_setpoint) scale down pos_ratio
*
* task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
*
* (o) global control line
*
* ^ pos_ratio
* |
* | |<===== global dirty control scope ======>|
* 2.0 .............*
* | .*
* | . *
* | . *
* | . *
* | . *
* | . *
* 1.0 ................................*
* | . . *
* | . . *
* | . . *
* | . . *
* | . . *
* 0 +------------.------------------.----------------------*------------->
* freerun^ setpoint^ limit^ dirty pages
*
* (o) bdi control line
*
* ^ pos_ratio
* |
* | *
* | *
* | *
* | *
* | * |<=========== span ============>|
* 1.0 .......................*
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* | . *
* 1/4 ...............................................* * * * * * * * * * * *
* | . .
* | . .
* | . .
* 0 +----------------------.-------------------------------.------------->
* bdi_setpoint^ x_intercept^
*
* The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
* be smoothly throttled down to normal if it starts high in situations like
* - start writing to a slow SD card and a fast disk at the same time. The SD
* card's bdi_dirty may rush to many times higher than bdi_setpoint.
* - the bdi dirty thresh drops quickly due to change of JBOD workload
*/
static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
unsigned long thresh,
unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty)
{
unsigned long write_bw = bdi->avg_write_bandwidth;
unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
unsigned long limit = hard_dirty_limit(thresh);
unsigned long x_intercept;
unsigned long setpoint; /* dirty pages' target balance point */
unsigned long bdi_setpoint;
unsigned long span;
long long pos_ratio; /* for scaling up/down the rate limit */
long x;

if (unlikely(dirty >= limit))
return 0;

/*
* global setpoint
*
* setpoint - dirty 3
* f(dirty) := 1.0 + (----------------)
* limit - setpoint
*
* it's a 3rd order polynomial that subjects to
*
* (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
* (2) f(setpoint) = 1.0 => the balance point
* (3) f(limit) = 0 => the hard limit
* (4) df/dx <= 0 => negative feedback control
* (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
* => fast response on large errors; small oscillation near setpoint
*/
setpoint = (freerun + limit) / 2;
x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
limit - setpoint + 1);
pos_ratio = x;
pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
pos_ratio += 1 << RATELIMIT_CALC_SHIFT;

/*
* We have computed basic pos_ratio above based on global situation. If
* the bdi is over/under its share of dirty pages, we want to scale
* pos_ratio further down/up. That is done by the following mechanism.
*/

/*
* bdi setpoint
*
* f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
*
* x_intercept - bdi_dirty
* := --------------------------
* x_intercept - bdi_setpoint
*
* The main bdi control line is a linear function that subjects to
*
* (1) f(bdi_setpoint) = 1.0
* (2) k = - 1 / (8 * write_bw) (in single bdi case)
* or equally: x_intercept = bdi_setpoint + 8 * write_bw
*
* For single bdi case, the dirty pages are observed to fluctuate
* regularly within range
* [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
* for various filesystems, where (2) can yield in a reasonable 12.5%
* fluctuation range for pos_ratio.
*
* For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
* own size, so move the slope over accordingly and choose a slope that
* yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
*/
if (unlikely(bdi_thresh > thresh))
bdi_thresh = thresh;
/*
* It's very possible that bdi_thresh is close to 0 not because the
* device is slow, but that it has remained inactive for long time.
* Honour such devices a reasonable good (hopefully IO efficient)
* threshold, so that the occasional writes won't be blocked and active
* writes can rampup the threshold quickly.
*/
bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
/*
* scale global setpoint to bdi's:
* bdi_setpoint = setpoint * bdi_thresh / thresh
*/
x = div_u64((u64)bdi_thresh << 16, thresh + 1);
bdi_setpoint = setpoint * (u64)x >> 16;
/*
* Use span=(8*write_bw) in single bdi case as indicated by
* (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
*
* bdi_thresh thresh - bdi_thresh
* span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
* thresh thresh
*/
span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
x_intercept = bdi_setpoint + span;

if (bdi_dirty < x_intercept - span / 4) {
pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
x_intercept - bdi_setpoint + 1);
} else
pos_ratio /= 4;

/*
* bdi reserve area, safeguard against dirty pool underrun and disk idle
* It may push the desired control point of global dirty pages higher
* than setpoint.
*/
x_intercept = bdi_thresh / 2;
if (bdi_dirty < x_intercept) {
if (bdi_dirty > x_intercept / 8)
pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
else
pos_ratio *= 8;
}

return pos_ratio;
}

static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
unsigned long elapsed,
unsigned long written)
{
const unsigned long period = roundup_pow_of_two(3 * HZ);
unsigned long avg = bdi->avg_write_bandwidth;
unsigned long old = bdi->write_bandwidth;
u64 bw;

/*
* bw = written * HZ / elapsed
*
* bw * elapsed + write_bandwidth * (period - elapsed)
* write_bandwidth = ---------------------------------------------------
* period
*/
bw = written - bdi->written_stamp;
bw *= HZ;
if (unlikely(elapsed > period)) {
do_div(bw, elapsed);
avg = bw;
goto out;
}
bw += (u64)bdi->write_bandwidth * (period - elapsed);
bw >>= ilog2(period);

/*
* one more level of smoothing, for filtering out sudden spikes
*/
if (avg > old && old >= (unsigned long)bw)
avg -= (avg - old) >> 3;

if (avg < old && old <= (unsigned long)bw)
avg += (old - avg) >> 3;

out:
bdi->write_bandwidth = bw;
bdi->avg_write_bandwidth = avg;
}

/*
* The global dirtyable memory and dirty threshold could be suddenly knocked
* down by a large amount (eg. on the startup of KVM in a swapless system).
* This may throw the system into deep dirty exceeded state and throttle
* heavy/light dirtiers alike. To retain good responsiveness, maintain
* global_dirty_limit for tracking slowly down to the knocked down dirty
* threshold.
*/
static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
{
unsigned long limit = global_dirty_limit;

/*
* Follow up in one step.
*/
if (limit < thresh) {
limit = thresh;
goto update;
}

/*
* Follow down slowly. Use the higher one as the target, because thresh
* may drop below dirty. This is exactly the reason to introduce
* global_dirty_limit which is guaranteed to lie above the dirty pages.
*/
thresh = max(thresh, dirty);
if (limit > thresh) {
limit -= (limit - thresh) >> 5;
goto update;
}
return;
update:
global_dirty_limit = limit;
}

static void global_update_bandwidth(unsigned long thresh,
unsigned long dirty,
unsigned long now)
{
static DEFINE_SPINLOCK(dirty_lock);
static unsigned long update_time;

/*
* check locklessly first to optimize away locking for the most time
*/
if (time_before(now, update_time + BANDWIDTH_INTERVAL))
return;

spin_lock(&dirty_lock);
if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
update_dirty_limit(thresh, dirty);
update_time = now;
}
spin_unlock(&dirty_lock);
}

/*
* Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
*
* Normal bdi tasks will be curbed at or below it in long term.
* Obviously it should be around (write_bw / N) when there are N dd tasks.
*/
static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
unsigned long thresh,
unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty,
unsigned long dirtied,
unsigned long elapsed)
{
unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
unsigned long limit = hard_dirty_limit(thresh);
unsigned long setpoint = (freerun + limit) / 2;
unsigned long write_bw = bdi->avg_write_bandwidth;
unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
unsigned long dirty_rate;
unsigned long task_ratelimit;
unsigned long balanced_dirty_ratelimit;
unsigned long pos_ratio;
unsigned long step;
unsigned long x;

/*
* The dirty rate will match the writeout rate in long term, except
* when dirty pages are truncated by userspace or re-dirtied by FS.
*/
dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;

pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
bdi_thresh, bdi_dirty);
/*
* task_ratelimit reflects each dd's dirty rate for the past 200ms.
*/
task_ratelimit = (u64)dirty_ratelimit *
pos_ratio >> RATELIMIT_CALC_SHIFT;
task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */

/*
* A linear estimation of the "balanced" throttle rate. The theory is,
* if there are N dd tasks, each throttled at task_ratelimit, the bdi's
* dirty_rate will be measured to be (N * task_ratelimit). So the below
* formula will yield the balanced rate limit (write_bw / N).
*
* Note that the expanded form is not a pure rate feedback:
* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
* but also takes pos_ratio into account:
* rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
*
* (1) is not realistic because pos_ratio also takes part in balancing
* the dirty rate. Consider the state
* pos_ratio = 0.5 (3)
* rate = 2 * (write_bw / N) (4)
* If (1) is used, it will stuck in that state! Because each dd will
* be throttled at
* task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
* yielding
* dirty_rate = N * task_ratelimit = write_bw (6)
* put (6) into (1) we get
* rate_(i+1) = rate_(i) (7)
*
* So we end up using (2) to always keep
* rate_(i+1) ~= (write_bw / N) (8)
* regardless of the value of pos_ratio. As long as (8) is satisfied,
* pos_ratio is able to drive itself to 1.0, which is not only where
* the dirty count meet the setpoint, but also where the slope of
* pos_ratio is most flat and hence task_ratelimit is least fluctuated.
*/
balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
dirty_rate | 1);

/*
* We could safely do this and return immediately:
*
* bdi->dirty_ratelimit = balanced_dirty_ratelimit;
*
* However to get a more stable dirty_ratelimit, the below elaborated
* code makes use of task_ratelimit to filter out sigular points and
* limit the step size.
*
* The below code essentially only uses the relative value of
*
* task_ratelimit - dirty_ratelimit
* = (pos_ratio - 1) * dirty_ratelimit
*
* which reflects the direction and size of dirty position error.
*/

/*
* dirty_ratelimit will follow balanced_dirty_ratelimit iff
* task_ratelimit is on the same side of dirty_ratelimit, too.
* For example, when
* - dirty_ratelimit > balanced_dirty_ratelimit
* - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
* lowering dirty_ratelimit will help meet both the position and rate
* control targets. Otherwise, don't update dirty_ratelimit if it will
* only help meet the rate target. After all, what the users ultimately
* feel and care are stable dirty rate and small position error.
*
* |task_ratelimit - dirty_ratelimit| is used to limit the step size
* and filter out the sigular points of balanced_dirty_ratelimit. Which
* keeps jumping around randomly and can even leap far away at times
* due to the small 200ms estimation period of dirty_rate (we want to
* keep that period small to reduce time lags).
*/
step = 0;
if (dirty < setpoint) {
x = min(bdi->balanced_dirty_ratelimit,
min(balanced_dirty_ratelimit, task_ratelimit));
if (dirty_ratelimit < x)
step = x - dirty_ratelimit;
} else {
x = max(bdi->balanced_dirty_ratelimit,
max(balanced_dirty_ratelimit, task_ratelimit));
if (dirty_ratelimit > x)
step = dirty_ratelimit - x;
}

/*
* Don't pursue 100% rate matching. It's impossible since the balanced
* rate itself is constantly fluctuating. So decrease the track speed
* when it gets close to the target. Helps eliminate pointless tremors.
*/
step >>= dirty_ratelimit / (2 * step + 1);
/*
* Limit the tracking speed to avoid overshooting.
*/
step = (step + 7) / 8;

if (dirty_ratelimit < balanced_dirty_ratelimit)
dirty_ratelimit += step;
else
dirty_ratelimit -= step;

bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;

trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
}

void __bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long thresh,
unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty,
unsigned long start_time)
{
unsigned long now = jiffies;
unsigned long elapsed = now - bdi->bw_time_stamp;
unsigned long dirtied;
unsigned long written;

/*
* rate-limit, only update once every 200ms.
*/
if (elapsed < BANDWIDTH_INTERVAL)
return;

dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);

/*
* Skip quiet periods when disk bandwidth is under-utilized.
* (at least 1s idle time between two flusher runs)
*/
if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
goto snapshot;

if (thresh) {
global_update_bandwidth(thresh, dirty, now);
bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
bdi_thresh, bdi_dirty,
dirtied, elapsed);
}
bdi_update_write_bandwidth(bdi, elapsed, written);

snapshot:
bdi->dirtied_stamp = dirtied;
bdi->written_stamp = written;
bdi->bw_time_stamp = now;
}

static void bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long thresh,
unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty,
unsigned long start_time)
{
if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
return;
spin_lock(&bdi->wb.list_lock);
__bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
bdi_thresh, bdi_dirty, start_time);
spin_unlock(&bdi->wb.list_lock);
}

/*
* After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
* will look to see if it needs to start dirty throttling.
*
* If dirty_poll_interval is too low, big NUMA machines will call the expensive
* global_page_state() too often. So scale it near-sqrt to the safety margin
* (the number of pages we may dirty without exceeding the dirty limits).
*/
static unsigned long dirty_poll_interval(unsigned long dirty,
unsigned long thresh)
{
if (thresh > dirty)
return 1UL << (ilog2(thresh - dirty) >> 1);

return 1;
}

static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
unsigned long bdi_dirty)
{
unsigned long bw = bdi->avg_write_bandwidth;
unsigned long hi = ilog2(bw);
unsigned long lo = ilog2(bdi->dirty_ratelimit);
unsigned long t;

/* target for 20ms max pause on 1-dd case */
t = HZ / 50;

/*
* Scale up pause time for concurrent dirtiers in order to reduce CPU
* overheads.
*
* (N * 20ms) on 2^N concurrent tasks.
*/
if (hi > lo)
t += (hi - lo) * (20 * HZ) / 1024;

/*
* Limit pause time for small memory systems. If sleeping for too long
* time, a small pool of dirty/writeback pages may go empty and disk go
* idle.
*
* 8 serves as the safety ratio.
*/
t = min(t, bdi_dirty * HZ / (8 * bw + 1));

/*
* The pause time will be settled within range (max_pause/4, max_pause).
* Apply a minimal value of 4 to get a non-zero max_pause/4.
*/
return clamp_val(t, 4, MAX_PAUSE);
}

/*
* 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 wait once crossing the (background_thresh + dirty_thresh) / 2.
* If we're over `background_thresh' then the writeback threads are woken to
* perform some writeout.
*/
static void balance_dirty_pages(struct address_space *mapping,
unsigned long pages_dirtied)
{
unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
unsigned long bdi_reclaimable;
unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
unsigned long bdi_dirty;
unsigned long freerun;
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
long pause = 0;
long uninitialized_var(max_pause);
bool dirty_exceeded = false;
unsigned long task_ratelimit;
unsigned long uninitialized_var(dirty_ratelimit);
unsigned long pos_ratio;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;

for (;;) {
/*
* 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.
*/
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);

global_dirty_limits(&background_thresh, &dirty_thresh);

/*
* Throttle it only when the background writeback cannot
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
freerun = dirty_freerun_ceiling(dirty_thresh,
background_thresh);
if (nr_dirty <= freerun)
break;

if (unlikely(!writeback_in_progress(bdi)))
bdi_start_background_writeback(bdi);

/*
* bdi_thresh is not treated as some limiting factor as
* dirty_thresh, due to reasons
* - in JBOD setup, bdi_thresh can fluctuate a lot
* - in a system with HDD and USB key, the USB key may somehow
* go into state (bdi_dirty >> bdi_thresh) either because
* bdi_dirty starts high, or because bdi_thresh drops low.
* In this case we don't want to hard throttle the USB key
* dirtiers for 100 seconds until bdi_dirty drops under
* bdi_thresh. Instead the auxiliary bdi control line in
* bdi_position_ratio() will let the dirtier task progress
* at some rate <= (write_bw / 2) for bringing down bdi_dirty.
*/
bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);

/*
* 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_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_reclaimable +
bdi_stat_sum(bdi, BDI_WRITEBACK);
} else {
bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_reclaimable +
bdi_stat(bdi, BDI_WRITEBACK);
}

dirty_exceeded = (bdi_dirty > bdi_thresh) ||
(nr_dirty > dirty_thresh);
if (dirty_exceeded && !bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;

bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
nr_dirty, bdi_thresh, bdi_dirty,
start_time);

max_pause = bdi_max_pause(bdi, bdi_dirty);

dirty_ratelimit = bdi->dirty_ratelimit;
pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
background_thresh, nr_dirty,
bdi_thresh, bdi_dirty);
task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
RATELIMIT_CALC_SHIFT;
if (unlikely(task_ratelimit == 0)) {
pause = max_pause;
goto pause;
}
pause = HZ * pages_dirtied / task_ratelimit;
if (unlikely(pause <= 0)) {
trace_balance_dirty_pages(bdi,
dirty_thresh,
background_thresh,
nr_dirty,
bdi_thresh,
bdi_dirty,
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
pause,
start_time);
pause = 1; /* avoid resetting nr_dirtied_pause below */
break;
}
pause = min(pause, max_pause);

pause:
trace_balance_dirty_pages(bdi,
dirty_thresh,
background_thresh,
nr_dirty,
bdi_thresh,
bdi_dirty,
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
pause,
start_time);
__set_current_state(TASK_KILLABLE);
io_schedule_timeout(pause);

/*
* This is typically equal to (nr_dirty < dirty_thresh) and can
* also keep "1000+ dd on a slow USB stick" under control.
*/
if (task_ratelimit)
break;

/*
* In the case of an unresponding NFS server and the NFS dirty
* pages exceeds dirty_thresh, give the other good bdi's a pipe
* to go through, so that tasks on them still remain responsive.
*
* In theory 1 page is enough to keep the comsumer-producer
* pipe going: the flusher cleans 1 page => the task dirties 1
* more page. However bdi_dirty has accounting errors. So use
* the larger and more IO friendly bdi_stat_error.
*/
if (bdi_dirty <= bdi_stat_error(bdi))
break;

if (fatal_signal_pending(current))
break;
}

if (!dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;

current->nr_dirtied = 0;
if (pause == 0) { /* in freerun area */
current->nr_dirtied_pause =
dirty_poll_interval(nr_dirty, dirty_thresh);
} else if (pause <= max_pause / 4 &&
pages_dirtied >= current->nr_dirtied_pause) {
current->nr_dirtied_pause = clamp_val(
dirty_ratelimit * (max_pause / 2) / HZ,
pages_dirtied + pages_dirtied / 8,
pages_dirtied * 4);
} else if (pause >= max_pause) {
current->nr_dirtied_pause = 1 | clamp_val(
dirty_ratelimit * (max_pause / 2) / HZ,
pages_dirtied / 4,
pages_dirtied - pages_dirtied / 8);
}

if (writeback_in_progress(bdi))
return;

/*
* 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)
return;

if (nr_reclaimable > background_thresh)
bdi_start_background_writeback(bdi);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
if (set_page_dirty(page) || page_mkwrite) {
struct address_space *mapping = page_mapping(page);

if (mapping)
balance_dirty_pages_ratelimited(mapping);
}
}

static DEFINE_PER_CPU(int, bdp_ratelimits);

/**
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
* @mapping: address_space which was dirtied
* @nr_pages_dirtied: number of pages which the caller has just dirtied
*
* 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.
*/
void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
unsigned long nr_pages_dirtied)
{
struct backing_dev_info *bdi = mapping->backing_dev_info;
int ratelimit;
int *p;

if (!bdi_cap_account_dirty(bdi))
return;

ratelimit = current->nr_dirtied_pause;
if (bdi->dirty_exceeded)
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));

current->nr_dirtied += nr_pages_dirtied;

preempt_disable();
/*
* This prevents one CPU to accumulate too many dirtied pages without
* calling into balance_dirty_pages(), which can happen when there are
* 1000+ tasks, all of them start dirtying pages at exactly the same
* time, hence all honoured too large initial task->nr_dirtied_pause.
*/
p = &__get_cpu_var(bdp_ratelimits);
if (unlikely(current->nr_dirtied >= ratelimit))
*p = 0;
else {
*p += nr_pages_dirtied;
if (unlikely(*p >= ratelimit_pages)) {
*p = 0;
ratelimit = 0;
}
}
preempt_enable();

if (unlikely(current->nr_dirtied >= ratelimit))
balance_dirty_pages(mapping, current->nr_dirtied);
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);

void throttle_vm_writeout(gfp_t gfp_mask)
{
unsigned long background_thresh;
unsigned long dirty_thresh;

        for ( ; ; ) {
global_dirty_limits(&background_thresh, &dirty_thresh);

                /*
* 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... */

                if (global_page_state(NR_UNSTABLE_NFS) +
global_page_state(NR_WRITEBACK) <= dirty_thresh)
                         break;
                congestion_wait(BLK_RW_ASYNC, HZ/10);

/*
* 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;
        }
}

/*
* sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
*/
int dirty_writeback_centisecs_handler(ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
proc_dointvec(table, write, buffer, length, ppos);
bdi_arm_supers_timer();
return 0;
}

#ifdef CONFIG_BLOCK
void laptop_mode_timer_fn(unsigned long data)
{
struct request_queue *q = (struct request_queue *)data;
int nr_pages = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);

/*
* We want to write everything out, not just down to the dirty
* threshold
*/
if (bdi_has_dirty_io(&q->backing_dev_info))
bdi_start_writeback(&q->backing_dev_info, nr_pages,
WB_REASON_LAPTOP_TIMER);
}

/*
* 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.
*/
void laptop_io_completion(struct backing_dev_info *info)
{
mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
}

/*
* 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)
{
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();
}
#endif

/*
* 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.
*/

void writeback_set_ratelimit(void)
{
unsigned long background_thresh;
unsigned long dirty_thresh;
global_dirty_limits(&background_thresh, &dirty_thresh);
ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
}

static int __cpuinit
ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
{
writeback_set_ratelimit();
return NOTIFY_DONE;
}

static struct notifier_block __cpuinitdata ratelimit_nb = {
.notifier_call = ratelimit_handler,
.next = NULL,
};

/*
* 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..
*/
void __init page_writeback_init(void)
{
int shift;

writeback_set_ratelimit();
register_cpu_notifier(&ratelimit_nb);

shift = calc_period_shift();
prop_descriptor_init(&vm_completions, shift);
}

/**
* 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)
{
#define WRITEBACK_TAG_BATCH 4096
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();
/* We check 'start' to handle wrapping when end == ~0UL */
} while (tagged >= WRITEBACK_TAG_BATCH && start);
}
EXPORT_SYMBOL(tag_pages_for_writeback);

/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
* @wbc: subtract the number of written pages from *@wbc->nr_to_write
* @writepage: function called for each page
* @data: data passed to writepage function
*
* If a page is already under I/O, write_cache_pages() skips it, even
* 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.
*
* 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).
*/
int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data)
{
int ret = 0;
int done = 0;
struct pagevec pvec;
int nr_pages;
pgoff_t uninitialized_var(writeback_index);
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
int cycled;
int range_whole = 0;
int tag;

pagevec_init(&pvec, 0);
if (wbc->range_cyclic) {
writeback_index = mapping->writeback_index; /* prev offset */
index = writeback_index;
if (index == 0)
cycled = 1;
else
cycled = 0;
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;
cycled = 1; /* ignore range_cyclic tests */
}
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
retry:
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag_pages_for_writeback(mapping, index, end);
done_index = index;
while (!done && (index <= end)) {
int i;

nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
if (nr_pages == 0)
break;

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

/*
* 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.
*/
if (page->index > end) {
/*
* can't be range_cyclic (1st pass) because
* end == -1 in that case.
*/
done = 1;
break;
}

done_index = page->index;

lock_page(page);

/*
* 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.
*/
if (unlikely(page->mapping != mapping)) {
continue_unlock:
unlock_page(page);
continue;
}

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;
}

BUG_ON(PageWriteback(page));
if (!clear_page_dirty_for_io(page))
goto continue_unlock;

trace_wbc_writepage(wbc, mapping->backing_dev_info);
ret = (*writepage)(page, wbc, data);
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_index = page->index + 1;
done = 1;
break;
}
}

/*
* We stop writing back only if we are not doing
* integrity sync. In case of integrity sync we have to
* keep going until we have written all the pages
* we tagged for writeback prior to entering this loop.
*/
if (--wbc->nr_to_write <= 0 &&
wbc->sync_mode == WB_SYNC_NONE) {
done = 1;
break;
}
}
pagevec_release(&pvec);
cond_resched();
}
if (!cycled && !done) {
/*
* range_cyclic:
* We hit the last page and there is more work to be done: wrap
* back to the start of the file
*/
cycled = 1;
index = 0;
end = writeback_index - 1;
goto retry;
}
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
mapping->writeback_index = done_index;

return ret;
}
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)
{
struct blk_plug plug;
int ret;

/* deal with chardevs and other special file */
if (!mapping->a_ops->writepage)
return 0;

blk_start_plug(&plug);
ret = write_cache_pages(mapping, wbc, __writepage, mapping);
blk_finish_plug(&plug);
return ret;
}

EXPORT_SYMBOL(generic_writepages);

int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
int ret;

if (wbc->nr_to_write <= 0)
return 0;
if (mapping->a_ops->writepages)
ret = mapping->a_ops->writepages(mapping, wbc);
else
ret = generic_writepages(mapping, wbc);
return ret;
}

/**
* write_one_page - write out a single page and optionally wait on I/O
* @page: the page to write
* @wait: if true, wait on writeout
*
* 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);

/*
* For address_spaces which do not use buffers nor write back.
*/
int __set_page_dirty_no_writeback(struct page *page)
{
if (!PageDirty(page))
return !TestSetPageDirty(page);
return 0;
}

/*
* 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_zone_page_state(page, NR_DIRTIED);
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
task_io_account_write(PAGE_CACHE_SIZE);
}
}
EXPORT_SYMBOL(account_page_dirtied);

/*
* Helper function for set_page_writeback family.
* NOTE: Unlike account_page_dirtied this does not rely on being atomic
* wrt interrupts.
*/
void account_page_writeback(struct page *page)
{
inc_zone_page_state(page, NR_WRITEBACK);
}
EXPORT_SYMBOL(account_page_writeback);

/*
* 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
* mapping by re-checking page_mapping() inside tree_lock.
*/
int __set_page_dirty_nobuffers(struct page *page)
{
if (!TestSetPageDirty(page)) {
struct address_space *mapping = page_mapping(page);
struct address_space *mapping2;

if (!mapping)
return 1;

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

/*
* 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.
*
* If the mapping doesn't provide a set_page_dirty a_op, then
* just fall through and assume that it wants buffer_heads.
*/
int set_page_dirty(struct page *page)
{
struct address_space *mapping = page_mapping(page);

if (likely(mapping)) {
int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
/*
* readahead/lru_deactivate_page could remain
* PG_readahead/PG_reclaim due to race with end_page_writeback
* About readahead, if the page is written, the flags would be
* reset. So no problem.
* About lru_deactivate_page, if the page is redirty, the flag
* will be reset. So no problem. but if the page is used by readahead
* it will confuse readahead and make it restart the size rampup
* process. But it's a trivial problem.
*/
ClearPageReclaim(page);
#ifdef CONFIG_BLOCK
if (!spd)
spd = __set_page_dirty_buffers;
#endif
return (*spd)(page);
}
if (!PageDirty(page)) {
if (!TestSetPageDirty(page))
return 1;
}
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;

lock_page(page);
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);

BUG_ON(!PageLocked(page));

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);
/*
* 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.
*/
if (TestClearPageDirty(page)) {
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
return 1;
}
return 0;
}
return TestClearPageDirty(page);
}
EXPORT_SYMBOL(clear_page_dirty_for_io);

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

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

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

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

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

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

}
EXPORT_SYMBOL(test_set_page_writeback);

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