--- /dev/null
+/*
+ * 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> /* __set_page_dirty_buffers */
+#include <linux/pagevec.h>
+#include <linux/timer.h>
+#include <linux/sched/rt.h>
+#include <linux/mm_inline.h>
+#include <trace/events/writeback.h>
+
+#include "internal.h"
+
+/*
+ * Sleep at most 200ms at a time in balance_dirty_pages().
+ */
+#define MAX_PAUSE max(HZ/5, 1)
+
+/*
+ * Try to keep balance_dirty_pages() call intervals higher than this many pages
+ * by raising pause time to max_pause when falls below it.
+ */
+#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
+
+/*
+ * 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 */
+
+EXPORT_SYMBOL_GPL(dirty_writeback_interval);
+
+/*
+ * 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 fprop_global writeout_completions;
+
+static void writeout_period(unsigned long t);
+/* Timer for aging of writeout_completions */
+static struct timer_list writeout_period_timer =
+ TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
+static unsigned long writeout_period_time = 0;
+
+/*
+ * Length of period for aging writeout fractions of bdis. This is an
+ * arbitrarily chosen number. The longer the period, the slower fractions will
+ * reflect changes in current writeout rate.
+ */
+#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
+
+/*
+ * In a memory zone, there is a certain amount of pages we consider
+ * available for the page cache, which is essentially the number of
+ * free and reclaimable pages, minus some zone reserves to protect
+ * lowmem and the ability to uphold the zone's watermarks without
+ * requiring writeback.
+ *
+ * This number of dirtyable pages is the base value of which the
+ * user-configurable dirty ratio is the effictive number of pages that
+ * are allowed to be actually dirtied. Per individual zone, or
+ * globally by using the sum of dirtyable pages over all zones.
+ *
+ * Because the user is allowed to specify the dirty limit globally as
+ * absolute number of bytes, calculating the per-zone dirty limit can
+ * require translating the configured limit into a percentage of
+ * global dirtyable memory first.
+ */
+
+/**
+ * zone_dirtyable_memory - number of dirtyable pages in a zone
+ * @zone: the zone
+ *
+ * Returns the zone's number of pages potentially available for dirty
+ * page cache. This is the base value for the per-zone dirty limits.
+ */
+static unsigned long zone_dirtyable_memory(struct zone *zone)
+{
+ unsigned long nr_pages;
+
+ nr_pages = zone_page_state(zone, NR_FREE_PAGES);
+ nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
+
+ nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
+ nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
+
+ return nr_pages;
+}
+
+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_dirtyable_memory(z);
+ }
+ /*
+ * Unreclaimable memory (kernel memory or anonymous memory
+ * without swap) can bring down the dirtyable pages below
+ * the zone's dirty balance reserve and the above calculation
+ * will underflow. However we still want to add in nodes
+ * which are below threshold (negative values) to get a more
+ * accurate calculation but make sure that the total never
+ * underflows.
+ */
+ if ((long)x < 0)
+ x = 0;
+
+ /*
+ * 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
+}
+
+/**
+ * global_dirtyable_memory - number of globally dirtyable pages
+ *
+ * Returns the global number of pages potentially available for dirty
+ * page cache. This is the base value for the global dirty limits.
+ */
+static unsigned long global_dirtyable_memory(void)
+{
+ unsigned long x;
+
+ x = global_page_state(NR_FREE_PAGES);
+ x -= min(x, dirty_balance_reserve);
+
+ x += global_page_state(NR_INACTIVE_FILE);
+ x += global_page_state(NR_ACTIVE_FILE);
+
+ if (!vm_highmem_is_dirtyable)
+ x -= highmem_dirtyable_memory(x);
+
+ return x + 1; /* Ensure that we never return 0 */
+}
+
+/*
+ * 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)
+{
+ const unsigned long available_memory = global_dirtyable_memory();
+ unsigned long background;
+ unsigned long dirty;
+ struct task_struct *tsk;
+
+ 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);
+}
+
+/**
+ * zone_dirty_limit - maximum number of dirty pages allowed in a zone
+ * @zone: the zone
+ *
+ * Returns the maximum number of dirty pages allowed in a zone, based
+ * on the zone's dirtyable memory.
+ */
+static unsigned long zone_dirty_limit(struct zone *zone)
+{
+ unsigned long zone_memory = zone_dirtyable_memory(zone);
+ struct task_struct *tsk = current;
+ unsigned long dirty;
+
+ if (vm_dirty_bytes)
+ dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
+ zone_memory / global_dirtyable_memory();
+ else
+ dirty = vm_dirty_ratio * zone_memory / 100;
+
+ if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
+ dirty += dirty / 4;
+
+ return dirty;
+}
+
+/**
+ * zone_dirty_ok - tells whether a zone is within its dirty limits
+ * @zone: the zone to check
+ *
+ * Returns %true when the dirty pages in @zone are within the zone's
+ * dirty limit, %false if the limit is exceeded.
+ */
+bool zone_dirty_ok(struct zone *zone)
+{
+ unsigned long limit = zone_dirty_limit(zone);
+
+ return zone_page_state(zone, NR_FILE_DIRTY) +
+ zone_page_state(zone, NR_UNSTABLE_NFS) +
+ zone_page_state(zone, NR_WRITEBACK) <= limit;
+}
+
+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) {
+ writeback_set_ratelimit();
+ 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) {
+ writeback_set_ratelimit();
+ vm_dirty_ratio = 0;
+ }
+ return ret;
+}
+
+static unsigned long wp_next_time(unsigned long cur_time)
+{
+ cur_time += VM_COMPLETIONS_PERIOD_LEN;
+ /* 0 has a special meaning... */
+ if (!cur_time)
+ return 1;
+ return cur_time;
+}
+
+/*
+ * 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);
+ __fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
+ bdi->max_prop_frac);
+ /* First event after period switching was turned off? */
+ if (!unlikely(writeout_period_time)) {
+ /*
+ * We can race with other __bdi_writeout_inc calls here but
+ * it does not cause any harm since the resulting time when
+ * timer will fire and what is in writeout_period_time will be
+ * roughly the same.
+ */
+ writeout_period_time = wp_next_time(jiffies);
+ mod_timer(&writeout_period_timer, writeout_period_time);
+ }
+}
+
+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)
+{
+ fprop_fraction_percpu(&writeout_completions, &bdi->completions,
+ numerator, denominator);
+}
+
+/*
+ * On idle system, we can be called long after we scheduled because we use
+ * deferred timers so count with missed periods.
+ */
+static void writeout_period(unsigned long t)
+{
+ int miss_periods = (jiffies - writeout_period_time) /
+ VM_COMPLETIONS_PERIOD_LEN;
+
+ if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
+ writeout_period_time = wp_next_time(writeout_period_time +
+ miss_periods * VM_COMPLETIONS_PERIOD_LEN);
+ mod_timer(&writeout_period_timer, writeout_period_time);
+ } else {
+ /*
+ * Aging has zeroed all fractions. Stop wasting CPU on period
+ * updates.
+ */
+ writeout_period_time = 0;
+ }
+}
+
+/*
+ * 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 = (FPROP_FRAC_BASE * max_ratio) / 100;
+ }
+ spin_unlock_bh(&bdi_lock);
+
+ return ret;
+}
+EXPORT_SYMBOL(bdi_set_max_ratio);
+
+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);
+}
+
+/**
+ * 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;
+}
+
+/*
+ * 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
+ */
+static long long pos_ratio_polynom(unsigned long setpoint,
+ unsigned long dirty,
+ unsigned long limit)
+{
+ long long pos_ratio;
+ long x;
+
+ x = div64_s64(((s64)setpoint - (s64)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;
+
+ return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
+}
+
+/*
+ * 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
+ *
+ * See comment for pos_ratio_polynom().
+ */
+ setpoint = (freerun + limit) / 2;
+ pos_ratio = pos_ratio_polynom(setpoint, dirty, limit);
+
+ /*
+ * The strictlimit feature is a tool preventing mistrusted filesystems
+ * from growing a large number of dirty pages before throttling. For
+ * such filesystems balance_dirty_pages always checks bdi counters
+ * against bdi limits. Even if global "nr_dirty" is under "freerun".
+ * This is especially important for fuse which sets bdi->max_ratio to
+ * 1% by default. Without strictlimit feature, fuse writeback may
+ * consume arbitrary amount of RAM because it is accounted in
+ * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
+ *
+ * Here, in bdi_position_ratio(), we calculate pos_ratio based on
+ * two values: bdi_dirty and bdi_thresh. Let's consider an example:
+ * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
+ * limits are set by default to 10% and 20% (background and throttle).
+ * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
+ * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
+ * about ~6K pages (as the average of background and throttle bdi
+ * limits). The 3rd order polynomial will provide positive feedback if
+ * bdi_dirty is under bdi_setpoint and vice versa.
+ *
+ * Note, that we cannot use global counters in these calculations
+ * because we want to throttle process writing to a strictlimit BDI
+ * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
+ * in the example above).
+ */
+ if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
+ long long bdi_pos_ratio;
+ unsigned long bdi_bg_thresh;
+
+ if (bdi_dirty < 8)
+ return min_t(long long, pos_ratio * 2,
+ 2 << RATELIMIT_CALC_SHIFT);
+
+ if (bdi_dirty >= bdi_thresh)
+ return 0;
+
+ bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
+ bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
+ bdi_bg_thresh);
+
+ if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
+ return 0;
+
+ bdi_pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
+ bdi_thresh);
+
+ /*
+ * Typically, for strictlimit case, bdi_setpoint << setpoint
+ * and pos_ratio >> bdi_pos_ratio. In the other words global
+ * state ("dirty") is not limiting factor and we have to
+ * make decision based on bdi counters. But there is an
+ * important case when global pos_ratio should get precedence:
+ * global limits are exceeded (e.g. due to activities on other
+ * BDIs) while given strictlimit BDI is below limit.
+ *
+ * "pos_ratio * bdi_pos_ratio" would work for the case above,
+ * but it would look too non-natural for the case of all
+ * activity in the system coming from a single strictlimit BDI
+ * with bdi->max_ratio == 100%.
+ *
+ * Note that min() below somewhat changes the dynamics of the
+ * control system. Normally, pos_ratio value can be well over 3
+ * (when globally we are at freerun and bdi is well below bdi
+ * setpoint). Now the maximum pos_ratio in the same situation
+ * is 2. We might want to tweak this if we observe the control
+ * system is too slow to adapt.
+ */
+ return min(pos_ratio, bdi_pos_ratio);
+ }
+
+ /*
+ * 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 = div64_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
+ *
+ * @written may have decreased due to account_page_redirty().
+ * Avoid underflowing @bw calculation.
+ */
+ bw = written - min(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 = INITIAL_JIFFIES;
+
+ /*
+ * 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);
+ /*
+ * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
+ */
+ if (unlikely(balanced_dirty_ratelimit > write_bw))
+ balanced_dirty_ratelimit = write_bw;
+
+ /*
+ * 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 singular 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 singular 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;
+
+ /*
+ * For strictlimit case, calculations above were based on bdi counters
+ * and limits (starting from pos_ratio = bdi_position_ratio() and up to
+ * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
+ * Hence, to calculate "step" properly, we have to use bdi_dirty as
+ * "dirty" and bdi_setpoint as "setpoint".
+ *
+ * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
+ * it's possible that bdi_thresh is close to zero due to inactivity
+ * of backing device (see the implementation of bdi_dirty_limit()).
+ */
+ if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
+ dirty = bdi_dirty;
+ if (bdi_dirty < 8)
+ setpoint = bdi_dirty + 1;
+ else
+ setpoint = (bdi_thresh +
+ bdi_dirty_limit(bdi, bg_thresh)) / 2;
+ }
+
+ if (dirty < setpoint) {
+ x = min3(bdi->balanced_dirty_ratelimit,
+ balanced_dirty_ratelimit, task_ratelimit);
+ if (dirty_ratelimit < x)
+ step = x - dirty_ratelimit;
+ } else {
+ x = max3(bdi->balanced_dirty_ratelimit,
+ 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()
+ * 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 t;
+
+ /*
+ * 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 = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
+ t++;
+
+ return min_t(unsigned long, t, MAX_PAUSE);
+}
+
+static long bdi_min_pause(struct backing_dev_info *bdi,
+ long max_pause,
+ unsigned long task_ratelimit,
+ unsigned long dirty_ratelimit,
+ int *nr_dirtied_pause)
+{
+ long hi = ilog2(bdi->avg_write_bandwidth);
+ long lo = ilog2(bdi->dirty_ratelimit);
+ long t; /* target pause */
+ long pause; /* estimated next pause */
+ int pages; /* target nr_dirtied_pause */
+
+ /* target for 10ms pause on 1-dd case */
+ t = max(1, HZ / 100);
+
+ /*
+ * Scale up pause time for concurrent dirtiers in order to reduce CPU
+ * overheads.
+ *
+ * (N * 10ms) on 2^N concurrent tasks.
+ */
+ if (hi > lo)
+ t += (hi - lo) * (10 * HZ) / 1024;
+
+ /*
+ * This is a bit convoluted. We try to base the next nr_dirtied_pause
+ * on the much more stable dirty_ratelimit. However the next pause time
+ * will be computed based on task_ratelimit and the two rate limits may
+ * depart considerably at some time. Especially if task_ratelimit goes
+ * below dirty_ratelimit/2 and the target pause is max_pause, the next
+ * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
+ * result task_ratelimit won't be executed faithfully, which could
+ * eventually bring down dirty_ratelimit.
+ *
+ * We apply two rules to fix it up:
+ * 1) try to estimate the next pause time and if necessary, use a lower
+ * nr_dirtied_pause so as not to exceed max_pause. When this happens,
+ * nr_dirtied_pause will be "dancing" with task_ratelimit.
+ * 2) limit the target pause time to max_pause/2, so that the normal
+ * small fluctuations of task_ratelimit won't trigger rule (1) and
+ * nr_dirtied_pause will remain as stable as dirty_ratelimit.
+ */
+ t = min(t, 1 + max_pause / 2);
+ pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+
+ /*
+ * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
+ * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
+ * When the 16 consecutive reads are often interrupted by some dirty
+ * throttling pause during the async writes, cfq will go into idles
+ * (deadline is fine). So push nr_dirtied_pause as high as possible
+ * until reaches DIRTY_POLL_THRESH=32 pages.
+ */
+ if (pages < DIRTY_POLL_THRESH) {
+ t = max_pause;
+ pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+ if (pages > DIRTY_POLL_THRESH) {
+ pages = DIRTY_POLL_THRESH;
+ t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
+ }
+ }
+
+ pause = HZ * pages / (task_ratelimit + 1);
+ if (pause > max_pause) {
+ t = max_pause;
+ pages = task_ratelimit * t / roundup_pow_of_two(HZ);
+ }
+
+ *nr_dirtied_pause = pages;
+ /*
+ * The minimal pause time will normally be half the target pause time.
+ */
+ return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
+}
+
+static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
+ unsigned long dirty_thresh,
+ unsigned long background_thresh,
+ unsigned long *bdi_dirty,
+ unsigned long *bdi_thresh,
+ unsigned long *bdi_bg_thresh)
+{
+ unsigned long bdi_reclaimable;
+
+ /*
+ * 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);
+
+ if (bdi_bg_thresh)
+ *bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh *
+ background_thresh,
+ dirty_thresh) : 0;
+
+ /*
+ * 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);
+ }
+}
+
+/*
+ * 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 nr_dirty; /* = file_dirty + writeback + unstable_nfs */
+ unsigned long background_thresh;
+ unsigned long dirty_thresh;
+ long period;
+ long pause;
+ long max_pause;
+ long min_pause;
+ int nr_dirtied_pause;
+ bool dirty_exceeded = false;
+ unsigned long task_ratelimit;
+ unsigned long dirty_ratelimit;
+ unsigned long pos_ratio;
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
+ unsigned long start_time = jiffies;
+
+ for (;;) {
+ unsigned long now = jiffies;
+ unsigned long uninitialized_var(bdi_thresh);
+ unsigned long thresh;
+ unsigned long uninitialized_var(bdi_dirty);
+ unsigned long dirty;
+ unsigned long bg_thresh;
+
+ /*
+ * 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);
+
+ if (unlikely(strictlimit)) {
+ bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
+ &bdi_dirty, &bdi_thresh, &bg_thresh);
+
+ dirty = bdi_dirty;
+ thresh = bdi_thresh;
+ } else {
+ dirty = nr_dirty;
+ thresh = dirty_thresh;
+ bg_thresh = background_thresh;
+ }
+
+ /*
+ * Throttle it only when the background writeback cannot
+ * catch-up. This avoids (excessively) small writeouts
+ * when the bdi limits are ramping up in case of !strictlimit.
+ *
+ * In strictlimit case make decision based on the bdi counters
+ * and limits. Small writeouts when the bdi limits are ramping
+ * up are the price we consciously pay for strictlimit-ing.
+ */
+ if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh)) {
+ current->dirty_paused_when = now;
+ current->nr_dirtied = 0;
+ current->nr_dirtied_pause =
+ dirty_poll_interval(dirty, thresh);
+ break;
+ }
+
+ if (unlikely(!writeback_in_progress(bdi)))
+ bdi_start_background_writeback(bdi);
+
+ if (!strictlimit)
+ bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
+ &bdi_dirty, &bdi_thresh, NULL);
+
+ dirty_exceeded = (bdi_dirty > bdi_thresh) &&
+ ((nr_dirty > dirty_thresh) || strictlimit);
+ 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);
+
+ 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;
+ max_pause = bdi_max_pause(bdi, bdi_dirty);
+ min_pause = bdi_min_pause(bdi, max_pause,
+ task_ratelimit, dirty_ratelimit,
+ &nr_dirtied_pause);
+
+ if (unlikely(task_ratelimit == 0)) {
+ period = max_pause;
+ pause = max_pause;
+ goto pause;
+ }
+ period = HZ * pages_dirtied / task_ratelimit;
+ pause = period;
+ if (current->dirty_paused_when)
+ pause -= now - current->dirty_paused_when;
+ /*
+ * For less than 1s think time (ext3/4 may block the dirtier
+ * for up to 800ms from time to time on 1-HDD; so does xfs,
+ * however at much less frequency), try to compensate it in
+ * future periods by updating the virtual time; otherwise just
+ * do a reset, as it may be a light dirtier.
+ */
+ if (pause < min_pause) {
+ trace_balance_dirty_pages(bdi,
+ dirty_thresh,
+ background_thresh,
+ nr_dirty,
+ bdi_thresh,
+ bdi_dirty,
+ dirty_ratelimit,
+ task_ratelimit,
+ pages_dirtied,
+ period,
+ min(pause, 0L),
+ start_time);
+ if (pause < -HZ) {
+ current->dirty_paused_when = now;
+ current->nr_dirtied = 0;
+ } else if (period) {
+ current->dirty_paused_when += period;
+ current->nr_dirtied = 0;
+ } else if (current->nr_dirtied_pause <= pages_dirtied)
+ current->nr_dirtied_pause += pages_dirtied;
+ break;
+ }
+ if (unlikely(pause > max_pause)) {
+ /* for occasional dropped task_ratelimit */
+ now += min(pause - max_pause, max_pause);
+ 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,
+ period,
+ pause,
+ start_time);
+ __set_current_state(TASK_KILLABLE);
+ io_schedule_timeout(pause);
+
+ current->dirty_paused_when = now + pause;
+ current->nr_dirtied = 0;
+ current->nr_dirtied_pause = nr_dirtied_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;
+
+ 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);
+}
+
+static DEFINE_PER_CPU(int, bdp_ratelimits);
+
+/*
+ * Normal tasks are throttled by
+ * loop {
+ * dirty tsk->nr_dirtied_pause pages;
+ * take a snap in balance_dirty_pages();
+ * }
+ * However there is a worst case. If every task exit immediately when dirtied
+ * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
+ * called to throttle the page dirties. The solution is to save the not yet
+ * throttled page dirties in dirty_throttle_leaks on task exit and charge them
+ * randomly into the running tasks. This works well for the above worst case,
+ * as the new task will pick up and accumulate the old task's leaked dirty
+ * count and eventually get throttled.
+ */
+DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
+
+/**
+ * balance_dirty_pages_ratelimited - balance dirty memory state
+ * @mapping: address_space which was 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(struct address_space *mapping)
+{
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ 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));
+
+ 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 = this_cpu_ptr(&bdp_ratelimits);
+ if (unlikely(current->nr_dirtied >= ratelimit))
+ *p = 0;
+ else if (unlikely(*p >= ratelimit_pages)) {
+ *p = 0;
+ ratelimit = 0;
+ }
+ /*
+ * Pick up the dirtied pages by the exited tasks. This avoids lots of
+ * short-lived tasks (eg. gcc invocations in a kernel build) escaping
+ * the dirty throttling and livelock other long-run dirtiers.
+ */
+ p = this_cpu_ptr(&dirty_throttle_leaks);
+ if (*p > 0 && current->nr_dirtied < ratelimit) {
+ unsigned long nr_pages_dirtied;
+ nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
+ *p -= nr_pages_dirtied;
+ current->nr_dirtied += nr_pages_dirtied;
+ }
+ preempt_enable();
+
+ if (unlikely(current->nr_dirtied >= ratelimit))
+ balance_dirty_pages(mapping, current->nr_dirtied);
+}
+EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
+
+void throttle_vm_writeout(gfp_t gfp_mask)
+{
+ unsigned long background_thresh;
+ unsigned long dirty_thresh;
+
+ for ( ; ; ) {
+ global_dirty_limits(&background_thresh, &dirty_thresh);
+ dirty_thresh = hard_dirty_limit(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(struct ctl_table *table, int write,
+ void __user *buffer, size_t *length, loff_t *ppos)
+{
+ proc_dointvec(table, write, buffer, length, ppos);
+ 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);
+ global_dirty_limit = dirty_thresh;
+ ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
+ if (ratelimit_pages < 16)
+ ratelimit_pages = 16;
+}
+
+static int
+ratelimit_handler(struct notifier_block *self, unsigned long action,
+ void *hcpu)
+{
+
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_ONLINE:
+ case CPU_DEAD:
+ writeback_set_ratelimit();
+ return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+
+static struct notifier_block 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)
+{
+ writeback_set_ratelimit();
+ register_cpu_notifier(&ratelimit_nb);
+
+ fprop_global_init(&writeout_completions, GFP_KERNEL);
+}
+
+/**
+ * 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, inode_to_bdi(mapping->host));
+ 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)
+{
+ trace_writeback_dirty_page(page, mapping);
+
+ if (mapping_cap_account_dirty(mapping)) {
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+
+ __inc_zone_page_state(page, NR_FILE_DIRTY);
+ __inc_zone_page_state(page, NR_DIRTIED);
+ __inc_bdi_stat(bdi, BDI_RECLAIMABLE);
+ __inc_bdi_stat(bdi, BDI_DIRTIED);
+ task_io_account_write(PAGE_CACHE_SIZE);
+ current->nr_dirtied++;
+ this_cpu_inc(bdp_ratelimits);
+ }
+}
+EXPORT_SYMBOL(account_page_dirtied);
+
+/*
+ * Helper function for deaccounting dirty page without writeback.
+ *
+ * Doing this should *normally* only ever be done when a page
+ * is truncated, and is not actually mapped anywhere at all. However,
+ * fs/buffer.c does this when it notices that somebody has cleaned
+ * out all the buffers on a page without actually doing it through
+ * the VM. Can you say "ext3 is horribly ugly"? Thought you could.
+ */
+void account_page_cleaned(struct page *page, struct address_space *mapping)
+{
+ if (mapping_cap_account_dirty(mapping)) {
+ dec_zone_page_state(page, NR_FILE_DIRTY);
+ dec_bdi_stat(inode_to_bdi(mapping->host), BDI_RECLAIMABLE);
+ task_io_account_cancelled_write(PAGE_CACHE_SIZE);
+ }
+}
+EXPORT_SYMBOL(account_page_cleaned);
+
+/*
+ * 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.
+ *
+ * The caller must ensure this doesn't race with truncation. Most will simply
+ * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
+ * the pte lock held, which also locks out truncation.
+ */
+int __set_page_dirty_nobuffers(struct page *page)
+{
+ if (!TestSetPageDirty(page)) {
+ struct address_space *mapping = page_mapping(page);
+ unsigned long flags;
+
+ if (!mapping)
+ return 1;
+
+ spin_lock_irqsave(&mapping->tree_lock, flags);
+ BUG_ON(page_mapping(page) != 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_irqrestore(&mapping->tree_lock, flags);
+ if (mapping->host) {
+ /* !PageAnon && !swapper_space */
+ __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+ }
+ return 1;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(__set_page_dirty_nobuffers);
+
+/*
+ * Call this whenever redirtying a page, to de-account the dirty counters
+ * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
+ * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
+ * systematic errors in balanced_dirty_ratelimit and the dirty pages position
+ * control.
+ */
+void account_page_redirty(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ if (mapping && mapping_cap_account_dirty(mapping)) {
+ current->nr_dirtied--;
+ dec_zone_page_state(page, NR_DIRTIED);
+ dec_bdi_stat(inode_to_bdi(mapping->host), BDI_DIRTIED);
+ }
+}
+EXPORT_SYMBOL(account_page_redirty);
+
+/*
+ * 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)
+{
+ int ret;
+
+ wbc->pages_skipped++;
+ ret = __set_page_dirty_nobuffers(page);
+ account_page_redirty(page);
+ return ret;
+}
+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.
+ */
+ if (PageReclaim(page))
+ 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 while dirtying the page, and pages are
+ * always locked coming in here, so we get the desired
+ * exclusion.
+ */
+ if (TestClearPageDirty(page)) {
+ dec_zone_page_state(page, NR_FILE_DIRTY);
+ dec_bdi_stat(inode_to_bdi(mapping->host),
+ 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);
+ struct mem_cgroup *memcg;
+ int ret;
+
+ memcg = mem_cgroup_begin_page_stat(page);
+ if (mapping) {
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ 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) {
+ mem_cgroup_dec_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK);
+ dec_zone_page_state(page, NR_WRITEBACK);
+ inc_zone_page_state(page, NR_WRITTEN);
+ }
+ mem_cgroup_end_page_stat(memcg);
+ return ret;
+}
+
+int __test_set_page_writeback(struct page *page, bool keep_write)
+{
+ struct address_space *mapping = page_mapping(page);
+ struct mem_cgroup *memcg;
+ int ret;
+
+ memcg = mem_cgroup_begin_page_stat(page);
+ if (mapping) {
+ struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ 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);
+ if (!keep_write)
+ 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) {
+ mem_cgroup_inc_page_stat(memcg, MEM_CGROUP_STAT_WRITEBACK);
+ inc_zone_page_state(page, NR_WRITEBACK);
+ }
+ mem_cgroup_end_page_stat(memcg);
+ 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);
+
+/**
+ * wait_for_stable_page() - wait for writeback to finish, if necessary.
+ * @page: The page to wait on.
+ *
+ * This function determines if the given page is related to a backing device
+ * that requires page contents to be held stable during writeback. If so, then
+ * it will wait for any pending writeback to complete.
+ */
+void wait_for_stable_page(struct page *page)
+{
+ if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
+ wait_on_page_writeback(page);
+}
+EXPORT_SYMBOL_GPL(wait_for_stable_page);
Code Review / kvmfornfv.git / blobdiff