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page-writeback.c
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page-writeback.c
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/*
* mm/page-writeback.c
*
* Copyright (C) 2002, Linus Torvalds.
* Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <[email protected]>
*
* Contains functions related to writing back dirty pages at the
* address_space level.
*
* 10Apr2002 Andrew Morton
* 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>
#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)
/*
* 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.
* It should be somewhat larger than dirtied pages to ensure that reasonably
* large amounts of I/O are submitted.
*/
static inline long sync_writeback_pages(unsigned long dirtied)
{
if (dirtied < ratelimit_pages)
dirtied = ratelimit_pages;
return dirtied + dirtied / 2;
}
/* 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;
static struct prop_descriptor vm_dirties;
/*
* 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);
prop_change_shift(&vm_dirties, shift);
}
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);
void task_dirty_inc(struct task_struct *tsk)
{
prop_inc_single(&vm_dirties, &tsk->dirties);
}
/*
* 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);
}
static inline void task_dirties_fraction(struct task_struct *tsk,
long *numerator, long *denominator)
{
prop_fraction_single(&vm_dirties, &tsk->dirties,
numerator, denominator);
}
/*
* task_dirty_limit - scale down dirty throttling threshold for one task
*
* task specific dirty limit:
*
* dirty -= (dirty/8) * p_{t}
*
* To protect light/slow dirtying tasks from heavier/fast ones, we start
* throttling individual tasks before reaching the bdi dirty limit.
* Relatively low thresholds will be allocated to heavy dirtiers. So when
* dirty pages grow large, heavy dirtiers will be throttled first, which will
* effectively curb the growth of dirty pages. Light dirtiers with high enough
* dirty threshold may never get throttled.
*/
#define TASK_LIMIT_FRACTION 8
static unsigned long task_dirty_limit(struct task_struct *tsk,
unsigned long bdi_dirty)
{
long numerator, denominator;
unsigned long dirty = bdi_dirty;
u64 inv = dirty / TASK_LIMIT_FRACTION;
task_dirties_fraction(tsk, &numerator, &denominator);
inv *= numerator;
do_div(inv, denominator);
dirty -= inv;
return max(dirty, bdi_dirty/2);
}
/* Minimum limit for any task */
static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
{
return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
}
/*
* 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 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.
* And the "limit" in the name is not seriously taken as hard limit in
* balance_dirty_pages().
*
* 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;
}
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);
}
void __bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long 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 written;
/*
* rate-limit, only update once every 200ms.
*/
if (elapsed < BANDWIDTH_INTERVAL)
return;
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_write_bandwidth(bdi, elapsed, written);
snapshot:
bdi->written_stamp = written;
bdi->bw_time_stamp = now;
}
static void bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long 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, dirty, bdi_thresh, bdi_dirty,
start_time);
spin_unlock(&bdi->wb.list_lock);
}
/*
* 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'.
* 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 write_chunk)
{
unsigned long nr_reclaimable, bdi_nr_reclaimable;
unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
unsigned long bdi_dirty;
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
unsigned long task_bdi_thresh;
unsigned long min_task_bdi_thresh;
unsigned long pages_written = 0;
unsigned long pause = 1;
bool dirty_exceeded = false;
bool clear_dirty_exceeded = true;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;
for (;;) {
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.
*/
if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
break;
bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
task_bdi_thresh = task_dirty_limit(current, bdi_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 (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_nr_reclaimable +
bdi_stat_sum(bdi, BDI_WRITEBACK);
} else {
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_nr_reclaimable +
bdi_stat(bdi, BDI_WRITEBACK);
}
/*
* The bdi thresh is somehow "soft" limit derived from the
* global "hard" limit. The former helps to prevent heavy IO
* bdi or process from holding back light ones; The latter is
* the last resort safeguard.
*/
dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
(nr_dirty > dirty_thresh);
clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
(nr_dirty <= dirty_thresh);
if (!dirty_exceeded)
break;
if (!bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
bdi_thresh, bdi_dirty, start_time);
/* 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.
* Only move pages to writeback if this bdi is over its
* threshold otherwise wait until the disk writes catch
* up.
*/
trace_balance_dirty_start(bdi);
if (bdi_nr_reclaimable > task_bdi_thresh) {
pages_written += writeback_inodes_wb(&bdi->wb,
write_chunk);
trace_balance_dirty_written(bdi, pages_written);
if (pages_written >= write_chunk)
break; /* We've done our duty */
}
__set_current_state(TASK_UNINTERRUPTIBLE);
io_schedule_timeout(pause);
trace_balance_dirty_wait(bdi);
dirty_thresh = hard_dirty_limit(dirty_thresh);
/*
* max-pause area. If dirty exceeded but still within this
* area, no need to sleep for more than 200ms: (a) 8 pages per
* 200ms is typically more than enough to curb heavy dirtiers;
* (b) the pause time limit makes the dirtiers more responsive.
*/
if (nr_dirty < dirty_thresh &&
bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 &&
time_after(jiffies, start_time + MAX_PAUSE))
break;
/*
* 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;
}
/* Clear dirty_exceeded flag only when no task can exceed the limit */
if (clear_dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;
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 && pages_written) ||
(!laptop_mode && (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(unsigned long, bdp_ratelimits) = 0;
/**
* 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;
unsigned long ratelimit;
unsigned long *p;
if (!bdi_cap_account_dirty(bdi))
return;
ratelimit = ratelimit_pages;
if (mapping->backing_dev_info->dirty_exceeded)
ratelimit = 8;
/*
* Check the rate limiting. Also, we do not want to throttle real-time
* tasks in balance_dirty_pages(). Period.
*/
preempt_disable();
p = &__get_cpu_var(bdp_ratelimits);
*p += nr_pages_dirtied;
if (unlikely(*p >= ratelimit)) {
ratelimit = sync_writeback_pages(*p);
*p = 0;
preempt_enable();
balance_dirty_pages(mapping, ratelimit);
return;
}
preempt_enable();
}
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);
}
/*
* 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 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.
*/
void writeback_set_ratelimit(void)
{
ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
}
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);
prop_descriptor_init(&vm_dirties, shift);
}