| /* |
| * 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 <trace/events/writeback.h> |
| |
| /* |
| * Sleep at most 200ms at a time in balance_dirty_pages(). |
| */ |
| #define MAX_PAUSE max(HZ/5, 1) |
| |
| /* |
| * Estimate write bandwidth at 200ms intervals. |
| */ |
| #define BANDWIDTH_INTERVAL max(HZ/5, 1) |
| |
| #define RATELIMIT_CALC_SHIFT 10 |
| |
| /* |
| * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited |
| * will look to see if it needs to force writeback or throttling. |
| */ |
| static long ratelimit_pages = 32; |
| |
| /* The following parameters are exported via /proc/sys/vm */ |
| |
| /* |
| * Start background writeback (via writeback threads) at this percentage |
| */ |
| int dirty_background_ratio = 10; |
| |
| /* |
| * dirty_background_bytes starts at 0 (disabled) so that it is a function of |
| * dirty_background_ratio * the amount of dirtyable memory |
| */ |
| unsigned long dirty_background_bytes; |
| |
| /* |
| * free highmem will not be subtracted from the total free memory |
| * for calculating free ratios if vm_highmem_is_dirtyable is true |
| */ |
| int vm_highmem_is_dirtyable; |
| |
| /* |
| * The generator of dirty data starts writeback at this percentage |
| */ |
| int vm_dirty_ratio = 20; |
| |
| /* |
| * vm_dirty_bytes starts at 0 (disabled) so that it is a function of |
| * vm_dirty_ratio * the amount of dirtyable memory |
| */ |
| unsigned long vm_dirty_bytes; |
| |
| /* |
| * The interval between `kupdate'-style writebacks |
| */ |
| unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */ |
| |
| /* |
| * The longest time for which data is allowed to remain dirty |
| */ |
| unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */ |
| |
| /* |
| * Flag that makes the machine dump writes/reads and block dirtyings. |
| */ |
| int block_dump; |
| |
| /* |
| * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies: |
| * a full sync is triggered after this time elapses without any disk activity. |
| */ |
| int laptop_mode; |
| |
| EXPORT_SYMBOL(laptop_mode); |
| |
| /* End of sysctl-exported parameters */ |
| |
| unsigned long global_dirty_limit; |
| |
| /* |
| * Scale the writeback cache size proportional to the relative writeout speeds. |
| * |
| * We do this by keeping a floating proportion between BDIs, based on page |
| * writeback completions [end_page_writeback()]. Those devices that write out |
| * pages fastest will get the larger share, while the slower will get a smaller |
| * share. |
| * |
| * We use page writeout completions because we are interested in getting rid of |
| * dirty pages. Having them written out is the primary goal. |
| * |
| * We introduce a concept of time, a period over which we measure these events, |
| * because demand can/will vary over time. The length of this period itself is |
| * measured in page writeback completions. |
| * |
| */ |
| static struct prop_descriptor vm_completions; |
| |
| /* |
| * 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) - z->dirty_balance_reserve; |
| } |
| /* |
| * 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. |
| */ |
| unsigned long global_dirtyable_memory(void) |
| { |
| unsigned long x; |
| |
| x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() - |
| dirty_balance_reserve; |
| |
| 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) |
| { |
| 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 = global_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); |
| } |
| |
| /* |
| * 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 * global_dirtyable_memory()) / |
| 100; |
| return 2 + ilog2(dirty_total - 1); |
| } |
| |
| /* |
| * update the period when the dirty threshold changes. |
| */ |
| static void update_completion_period(void) |
| { |
| int shift = calc_period_shift(); |
| prop_change_shift(&vm_completions, shift); |
| |
| writeback_set_ratelimit(); |
| } |
| |
| int dirty_background_ratio_handler(struct ctl_table *table, int write, |
| void __user *buffer, size_t *lenp, |
| loff_t *ppos) |
| { |
| int ret; |
| |
| ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
| if (ret == 0 && write) |
| dirty_background_bytes = 0; |
| return ret; |
| } |
| |
| int dirty_background_bytes_handler(struct ctl_table *table, int write, |
| void __user *buffer, size_t *lenp, |
| loff_t *ppos) |
| { |
| int ret; |
| |
| ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
| if (ret == 0 && write) |
| dirty_background_ratio = 0; |
| return ret; |
| } |
| |
| int dirty_ratio_handler(struct ctl_table *table, int write, |
| void __user *buffer, size_t *lenp, |
| loff_t *ppos) |
| { |
| int old_ratio = vm_dirty_ratio; |
| int ret; |
| |
| ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); |
| if (ret == 0 && write && vm_dirty_ratio != old_ratio) { |
| update_completion_period(); |
| vm_dirty_bytes = 0; |
| } |
| return ret; |
| } |
| |
| int dirty_bytes_handler(struct ctl_table *table, int write, |
| void __user *buffer, size_t *lenp, |
| loff_t *ppos) |
| { |
| unsigned long old_bytes = vm_dirty_bytes; |
| int ret; |
| |
| ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos); |
| if (ret == 0 && write && vm_dirty_bytes != old_bytes) { |
| update_completion_period(); |
| vm_dirty_ratio = 0; |
| } |
| return ret; |
| } |
| |
| /* |
| * Increment the BDI's writeout completion count and the global writeout |
| * completion count. Called from test_clear_page_writeback(). |
| */ |
| static inline void __bdi_writeout_inc(struct backing_dev_info *bdi) |
| { |
| __inc_bdi_stat(bdi, BDI_WRITTEN); |
| __prop_inc_percpu_max(&vm_completions, &bdi->completions, |
| bdi->max_prop_frac); |
| } |
| |
| void bdi_writeout_inc(struct backing_dev_info *bdi) |
| { |
| unsigned long flags; |
| |
| local_irq_save(flags); |
| __bdi_writeout_inc(bdi); |
| local_irq_restore(flags); |
| } |
| EXPORT_SYMBOL_GPL(bdi_writeout_inc); |
| |
| /* |
| * Obtain an accurate fraction of the BDI's portion. |
| */ |
| static void bdi_writeout_fraction(struct backing_dev_info *bdi, |
| long *numerator, long *denominator) |
| { |
| prop_fraction_percpu(&vm_completions, &bdi->completions, |
| numerator, denominator); |
| } |
| |
| /* |
| * bdi_min_ratio keeps the sum of the minimum dirty shares of all |
| * registered backing devices, which, for obvious reasons, can not |
| * exceed 100%. |
| */ |
| static unsigned int bdi_min_ratio; |
| |
| int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) |
| { |
| int ret = 0; |
| |
| spin_lock_bh(&bdi_lock); |
| if (min_ratio > bdi->max_ratio) { |
| ret = -EINVAL; |
| } else { |
| min_ratio -= bdi->min_ratio; |
| if (bdi_min_ratio + min_ratio < 100) { |
| bdi_min_ratio += min_ratio; |
| bdi->min_ratio += min_ratio; |
| } else { |
| ret = -EINVAL; |
| } |
| } |
| spin_unlock_bh(&bdi_lock); |
| |
| return ret; |
| } |
| |
| int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) |
| { |
| int ret = 0; |
| |
| if (max_ratio > 100) |
| return -EINVAL; |
| |
| spin_lock_bh(&bdi_lock); |
| if (bdi->min_ratio > max_ratio) { |
| ret = -EINVAL; |
| } else { |
| bdi->max_ratio = max_ratio; |
| bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100; |
| } |
| spin_unlock_bh(&bdi_lock); |
| |
| return ret; |
| } |
| EXPORT_SYMBOL(bdi_set_max_ratio); |
| |
| 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; |
| } |
| |
| /* |
| * Dirty position control. |
| * |
| * (o) global/bdi setpoints |
| * |
| * We want the dirty pages be balanced around the global/bdi setpoints. |
| * When the number of dirty pages is higher/lower than the setpoint, the |
| * dirty position control ratio (and hence task dirty ratelimit) will be |
| * decreased/increased to bring the dirty pages back to the setpoint. |
| * |
| * pos_ratio = 1 << RATELIMIT_CALC_SHIFT |
| * |
| * if (dirty < setpoint) scale up pos_ratio |
| * if (dirty > setpoint) scale down pos_ratio |
| * |
| * if (bdi_dirty < bdi_setpoint) scale up pos_ratio |
| * if (bdi_dirty > bdi_setpoint) scale down pos_ratio |
| * |
| * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT |
| * |
| * (o) global control line |
| * |
| * ^ pos_ratio |
| * | |
| * | |<===== global dirty control scope ======>| |
| * 2.0 .............* |
| * | .* |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * 1.0 ................................* |
| * | . . * |
| * | . . * |
| * | . . * |
| * | . . * |
| * | . . * |
| * 0 +------------.------------------.----------------------*-------------> |
| * freerun^ setpoint^ limit^ dirty pages |
| * |
| * (o) bdi control line |
| * |
| * ^ pos_ratio |
| * | |
| * | * |
| * | * |
| * | * |
| * | * |
| * | * |<=========== span ============>| |
| * 1.0 .......................* |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * | . * |
| * 1/4 ...............................................* * * * * * * * * * * * |
| * | . . |
| * | . . |
| * | . . |
| * 0 +----------------------.-------------------------------.-------------> |
| * bdi_setpoint^ x_intercept^ |
| * |
| * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can |
| * be smoothly throttled down to normal if it starts high in situations like |
| * - start writing to a slow SD card and a fast disk at the same time. The SD |
| * card's bdi_dirty may rush to many times higher than bdi_setpoint. |
| * - the bdi dirty thresh drops quickly due to change of JBOD workload |
| */ |
| static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, |
| unsigned long thresh, |
| unsigned long bg_thresh, |
| unsigned long dirty, |
| unsigned long bdi_thresh, |
| unsigned long bdi_dirty) |
| { |
| unsigned long write_bw = bdi->avg_write_bandwidth; |
| unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
| unsigned long limit = hard_dirty_limit(thresh); |
| unsigned long x_intercept; |
| unsigned long setpoint; /* dirty pages' target balance point */ |
| unsigned long bdi_setpoint; |
| unsigned long span; |
| long long pos_ratio; /* for scaling up/down the rate limit */ |
| long x; |
| |
| if (unlikely(dirty >= limit)) |
| return 0; |
| |
| /* |
| * global setpoint |
| * |
| * setpoint - dirty 3 |
| * f(dirty) := 1.0 + (----------------) |
| * limit - setpoint |
| * |
| * it's a 3rd order polynomial that subjects to |
| * |
| * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast |
| * (2) f(setpoint) = 1.0 => the balance point |
| * (3) f(limit) = 0 => the hard limit |
| * (4) df/dx <= 0 => negative feedback control |
| * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) |
| * => fast response on large errors; small oscillation near setpoint |
| */ |
| setpoint = (freerun + limit) / 2; |
| x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT, |
| limit - setpoint + 1); |
| pos_ratio = x; |
| pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
| pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; |
| pos_ratio += 1 << RATELIMIT_CALC_SHIFT; |
| |
| /* |
| * We have computed basic pos_ratio above based on global situation. If |
| * the bdi is over/under its share of dirty pages, we want to scale |
| * pos_ratio further down/up. That is done by the following mechanism. |
| */ |
| |
| /* |
| * bdi setpoint |
| * |
| * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint) |
| * |
| * x_intercept - bdi_dirty |
| * := -------------------------- |
| * x_intercept - bdi_setpoint |
| * |
| * The main bdi control line is a linear function that subjects to |
| * |
| * (1) f(bdi_setpoint) = 1.0 |
| * (2) k = - 1 / (8 * write_bw) (in single bdi case) |
| * or equally: x_intercept = bdi_setpoint + 8 * write_bw |
| * |
| * For single bdi case, the dirty pages are observed to fluctuate |
| * regularly within range |
| * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2] |
| * for various filesystems, where (2) can yield in a reasonable 12.5% |
| * fluctuation range for pos_ratio. |
| * |
| * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its |
| * own size, so move the slope over accordingly and choose a slope that |
| * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh. |
| */ |
| if (unlikely(bdi_thresh > thresh)) |
| bdi_thresh = thresh; |
| /* |
| * It's very possible that bdi_thresh is close to 0 not because the |
| * device is slow, but that it has remained inactive for long time. |
| * Honour such devices a reasonable good (hopefully IO efficient) |
| * threshold, so that the occasional writes won't be blocked and active |
| * writes can rampup the threshold quickly. |
| */ |
| bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); |
| /* |
| * scale global setpoint to bdi's: |
| * bdi_setpoint = setpoint * bdi_thresh / thresh |
| */ |
| x = div_u64((u64)bdi_thresh << 16, thresh + 1); |
| bdi_setpoint = setpoint * (u64)x >> 16; |
| /* |
| * Use span=(8*write_bw) in single bdi case as indicated by |
| * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case. |
| * |
| * bdi_thresh thresh - bdi_thresh |
| * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh |
| * thresh thresh |
| */ |
| span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16; |
| x_intercept = bdi_setpoint + span; |
| |
| if (bdi_dirty < x_intercept - span / 4) { |
| pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), |
| x_intercept - bdi_setpoint + 1); |
| } else |
| pos_ratio /= 4; |
| |
| /* |
| * bdi reserve area, safeguard against dirty pool underrun and disk idle |
| * It may push the desired control point of global dirty pages higher |
| * than setpoint. |
| */ |
| x_intercept = bdi_thresh / 2; |
| if (bdi_dirty < x_intercept) { |
| if (bdi_dirty > x_intercept / 8) |
| pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty); |
| else |
| pos_ratio *= 8; |
| } |
| |
| return pos_ratio; |
| } |
| |
| static void bdi_update_write_bandwidth(struct backing_dev_info *bdi, |
| unsigned long elapsed, |
| unsigned long written) |
| { |
| const unsigned long period = roundup_pow_of_two(3 * HZ); |
| unsigned long avg = bdi->avg_write_bandwidth; |
| unsigned long old = bdi->write_bandwidth; |
| u64 bw; |
| |
| /* |
| * bw = written * HZ / elapsed |
| * |
| * bw * elapsed + write_bandwidth * (period - elapsed) |
| * write_bandwidth = --------------------------------------------------- |
| * period |
| */ |
| bw = written - bdi->written_stamp; |
| bw *= HZ; |
| if (unlikely(elapsed > period)) { |
| do_div(bw, elapsed); |
| avg = bw; |
| goto out; |
| } |
| bw += (u64)bdi->write_bandwidth * (period - elapsed); |
| bw >>= ilog2(period); |
| |
| /* |
| * one more level of smoothing, for filtering out sudden spikes |
| */ |
| if (avg > old && old >= (unsigned long)bw) |
| avg -= (avg - old) >> 3; |
| |
| if (avg < old && old <= (unsigned long)bw) |
| avg += (old - avg) >> 3; |
| |
| out: |
| bdi->write_bandwidth = bw; |
| bdi->avg_write_bandwidth = avg; |
| } |
| |
| /* |
| * The global dirtyable memory and dirty threshold could be suddenly knocked |
| * down by a large amount (eg. on the startup of KVM in a swapless system). |
| * This may throw the system into deep dirty exceeded state and throttle |
| * heavy/light dirtiers alike. To retain good responsiveness, maintain |
| * global_dirty_limit for tracking slowly down to the knocked down dirty |
| * threshold. |
| */ |
| static void update_dirty_limit(unsigned long thresh, unsigned long dirty) |
| { |
| unsigned long limit = global_dirty_limit; |
| |
| /* |
| * Follow up in one step. |
| */ |
| if (limit < thresh) { |
| limit = thresh; |
| goto update; |
| } |
| |
| /* |
| * Follow down slowly. Use the higher one as the target, because thresh |
| * may drop below dirty. This is exactly the reason to introduce |
| * global_dirty_limit which is guaranteed to lie above the dirty pages. |
| */ |
| thresh = max(thresh, dirty); |
| if (limit > thresh) { |
| limit -= (limit - thresh) >> 5; |
| goto update; |
| } |
| return; |
| update: |
| global_dirty_limit = limit; |
| } |
| |
| static void global_update_bandwidth(unsigned long thresh, |
| unsigned long dirty, |
| unsigned long now) |
| { |
| static DEFINE_SPINLOCK(dirty_lock); |
| static unsigned long update_time; |
| |
| /* |
| * check locklessly first to optimize away locking for the most time |
| */ |
| if (time_before(now, update_time + BANDWIDTH_INTERVAL)) |
| return; |
| |
| spin_lock(&dirty_lock); |
| if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) { |
| update_dirty_limit(thresh, dirty); |
| update_time = now; |
| } |
| spin_unlock(&dirty_lock); |
| } |
| |
| /* |
| * Maintain bdi->dirty_ratelimit, the base dirty throttle rate. |
| * |
| * Normal bdi tasks will be curbed at or below it in long term. |
| * Obviously it should be around (write_bw / N) when there are N dd tasks. |
| */ |
| static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi, |
| unsigned long thresh, |
| unsigned long bg_thresh, |
| unsigned long dirty, |
| unsigned long bdi_thresh, |
| unsigned long bdi_dirty, |
| unsigned long dirtied, |
| unsigned long elapsed) |
| { |
| unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh); |
| unsigned long limit = hard_dirty_limit(thresh); |
| unsigned long setpoint = (freerun + limit) / 2; |
| unsigned long write_bw = bdi->avg_write_bandwidth; |
| unsigned long dirty_ratelimit = bdi->dirty_ratelimit; |
| unsigned long dirty_rate; |
| unsigned long task_ratelimit; |
| unsigned long balanced_dirty_ratelimit; |
| unsigned long pos_ratio; |
| unsigned long step; |
| unsigned long x; |
| |
| /* |
| * The dirty rate will match the writeout rate in long term, except |
| * when dirty pages are truncated by userspace or re-dirtied by FS. |
| */ |
| dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed; |
| |
| pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty, |
| bdi_thresh, bdi_dirty); |
| /* |
| * task_ratelimit reflects each dd's dirty rate for the past 200ms. |
| */ |
| task_ratelimit = (u64)dirty_ratelimit * |
| pos_ratio >> RATELIMIT_CALC_SHIFT; |
| task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */ |
| |
| /* |
| * A linear estimation of the "balanced" throttle rate. The theory is, |
| * if there are N dd tasks, each throttled at task_ratelimit, the bdi's |
| * dirty_rate will be measured to be (N * task_ratelimit). So the below |
| * formula will yield the balanced rate limit (write_bw / N). |
| * |
| * Note that the expanded form is not a pure rate feedback: |
| * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1) |
| * but also takes pos_ratio into account: |
| * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2) |
| * |
| * (1) is not realistic because pos_ratio also takes part in balancing |
| * the dirty rate. Consider the state |
| * pos_ratio = 0.5 (3) |
| * rate = 2 * (write_bw / N) (4) |
| * If (1) is used, it will stuck in that state! Because each dd will |
| * be throttled at |
| * task_ratelimit = pos_ratio * rate = (write_bw / N) (5) |
| * yielding |
| * dirty_rate = N * task_ratelimit = write_bw (6) |
| * put (6) into (1) we get |
| * rate_(i+1) = rate_(i) (7) |
| * |
| * So we end up using (2) to always keep |
| * rate_(i+1) ~= (write_bw / N) (8) |
| * regardless of the value of pos_ratio. As long as (8) is satisfied, |
| * pos_ratio is able to drive itself to 1.0, which is not only where |
| * the dirty count meet the setpoint, but also where the slope of |
| * pos_ratio is most flat and hence task_ratelimit is least fluctuated. |
| */ |
| balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw, |
| dirty_rate | 1); |
| |
| /* |
| * We could safely do this and return immediately: |
| * |
| * bdi->dirty_ratelimit = balanced_dirty_ratelimit; |
| * |
| * However to get a more stable dirty_ratelimit, the below elaborated |
| * code makes use of task_ratelimit to filter out sigular points and |
| * limit the step size. |
| * |
| * The below code essentially only uses the relative value of |
| * |
| * task_ratelimit - dirty_ratelimit |
| * = (pos_ratio - 1) * dirty_ratelimit |
| * |
| * which reflects the direction and size of dirty position error. |
| */ |
| |
| /* |
| * dirty_ratelimit will follow balanced_dirty_ratelimit iff |
| * task_ratelimit is on the same side of dirty_ratelimit, too. |
| * For example, when |
| * - dirty_ratelimit > balanced_dirty_ratelimit |
| * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint) |
| * lowering dirty_ratelimit will help meet both the position and rate |
| * control targets. Otherwise, don't update dirty_ratelimit if it will |
| * only help meet the rate target. After all, what the users ultimately |
| * feel and care are stable dirty rate and small position error. |
| * |
| * |task_ratelimit - dirty_ratelimit| is used to limit the step size |
| * and filter out the sigular points of balanced_dirty_ratelimit. Which |
| * keeps jumping around randomly and can even leap far away at times |
| * due to the small 200ms estimation period of dirty_rate (we want to |
| * keep that period small to reduce time lags). |
| */ |
| step = 0; |
| if (dirty < setpoint) { |
| x = min(bdi->balanced_dirty_ratelimit, |
| min(balanced_dirty_ratelimit, task_ratelimit)); |
| if (dirty_ratelimit < x) |
| step = x - dirty_ratelimit; |
| } else { |
| x = max(bdi->balanced_dirty_ratelimit, |
| max(balanced_dirty_ratelimit, task_ratelimit)); |
| if (dirty_ratelimit > x) |
| step = dirty_ratelimit - x; |
| } |
| |
| /* |
| * Don't pursue 100% rate matching. It's impossible since the balanced |
| * rate itself is constantly fluctuating. So decrease the track speed |
| * when it gets close to the target. Helps eliminate pointless tremors. |
| */ |
| step >>= dirty_ratelimit / (2 * step + 1); |
| /* |
| * Limit the tracking speed to avoid overshooting. |
| */ |
| step = (step + 7) / 8; |
| |
| if (dirty_ratelimit < balanced_dirty_ratelimit) |
| dirty_ratelimit += step; |
| else |
| dirty_ratelimit -= step; |
| |
| bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL); |
| bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit; |
| |
| trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit); |
| } |
| |
| void __bdi_update_bandwidth(struct backing_dev_info *bdi, |
| unsigned long thresh, |
| unsigned long bg_thresh, |
| unsigned long dirty, |
| unsigned long bdi_thresh, |
| unsigned long bdi_dirty, |
| unsigned long start_time) |
| { |
| unsigned long now = jiffies; |
| unsigned long elapsed = now - bdi->bw_time_stamp; |
| unsigned long dirtied; |
| unsigned long written; |
| |
| /* |
| * rate-limit, only update once every 200ms. |
| */ |
| if (elapsed < BANDWIDTH_INTERVAL) |
| return; |
| |
| dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]); |
| written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]); |
| |
| /* |
| * Skip quiet periods when disk bandwidth is under-utilized. |
| * (at least 1s idle time between two flusher runs) |
| */ |
| if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time)) |
| goto snapshot; |
| |
| if (thresh) { |
| global_update_bandwidth(thresh, dirty, now); |
| bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty, |
| bdi_thresh, bdi_dirty, |
| dirtied, elapsed); |
| } |
| bdi_update_write_bandwidth(bdi, elapsed, written); |
| |
| snapshot: |
| bdi->dirtied_stamp = dirtied; |
| bdi->written_stamp = written; |
| bdi->bw_time_stamp = now; |
| } |
| |
| static void bdi_update_bandwidth(struct backing_dev_info *bdi, |
| unsigned long thresh, |
| unsigned long bg_thresh, |
| unsigned long dirty, |
| unsigned long bdi_thresh, |
| unsigned long bdi_dirty, |
| unsigned long start_time) |
| { |
| if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL)) |
| return; |
| spin_lock(&bdi->wb.list_lock); |
| __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty, |
| bdi_thresh, bdi_dirty, start_time); |
| spin_unlock(&bdi->wb.list_lock); |
| } |
| |
| /* |
| * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr() |
| * will look to see if it needs to start dirty throttling. |
| * |
| * If dirty_poll_interval is too low, big NUMA machines will call the expensive |
| * global_page_state() too often. So scale it near-sqrt to the safety margin |
| * (the number of pages we may dirty without exceeding the dirty limits). |
| */ |
| static unsigned long dirty_poll_interval(unsigned long dirty, |
| unsigned long thresh) |
| { |
| if (thresh > dirty) |
| return 1UL << (ilog2(thresh - dirty) >> 1); |
| |
| return 1; |
| } |
| |
| static unsigned long bdi_max_pause(struct backing_dev_info *bdi, |
| unsigned long bdi_dirty) |
| { |
| unsigned long bw = bdi->avg_write_bandwidth; |
| unsigned long hi = ilog2(bw); |
| unsigned long lo = ilog2(bdi->dirty_ratelimit); |
| unsigned long t; |
| |
| /* target for 20ms max pause on 1-dd case */ |
| t = HZ / 50; |
| |
| /* |
| * Scale up pause time for concurrent dirtiers in order to reduce CPU |
| * overheads. |
| * |
| * (N * 20ms) on 2^N concurrent tasks. |
| */ |
| if (hi > lo) |
| t += (hi - lo) * (20 * HZ) / 1024; |
| |
| /* |
| * Limit pause time for small memory systems. If sleeping for too long |
| * time, a small pool of dirty/writeback pages may go empty and disk go |
| * idle. |
| * |
| * 8 serves as the safety ratio. |
| */ |
| t = min(t, bdi_dirty * HZ / (8 * bw + 1)); |
| |
| /* |
| * The pause time will be settled within range (max_pause/4, max_pause). |
| * Apply a minimal value of 4 to get a non-zero max_pause/4. |
| */ |
| return clamp_val(t, 4, MAX_PAUSE); |
| } |
| |
| /* |
| * balance_dirty_pages() must be called by processes which are generating dirty |
| * data. It looks at the number of dirty pages in the machine and will force |
| * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2. |
| * If we're over `background_thresh' then the writeback threads are woken to |
| * perform some writeout. |
| */ |
| static void balance_dirty_pages(struct address_space *mapping, |
| unsigned long pages_dirtied) |
| { |
| unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */ |
| unsigned long bdi_reclaimable; |
| unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */ |
| unsigned long bdi_dirty; |
| unsigned long freerun; |
| unsigned long background_thresh; |
| unsigned long dirty_thresh; |
| unsigned long bdi_thresh; |
| long pause = 0; |
| long uninitialized_var(max_pause); |
| bool dirty_exceeded = false; |
| unsigned long task_ratelimit; |
| unsigned long uninitialized_var(dirty_ratelimit); |
| unsigned long pos_ratio; |
| struct backing_dev_info *bdi = mapping->backing_dev_info; |
| unsigned long start_time = jiffies; |
| |
| for (;;) { |
| /* |
| * Unstable writes are a feature of certain networked |
| * filesystems (i.e. NFS) in which data may have been |
| * written to the server's write cache, but has not yet |
| * been flushed to permanent storage. |
| */ |
| nr_reclaimable = global_page_state(NR_FILE_DIRTY) + |
| global_page_state(NR_UNSTABLE_NFS); |
| nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK); |
| |
| global_dirty_limits(&background_thresh, &dirty_thresh); |
| |
| /* |
| * Throttle it only when the background writeback cannot |
| * catch-up. This avoids (excessively) small writeouts |
| * when the bdi limits are ramping up. |
| */ |
| freerun = dirty_freerun_ceiling(dirty_thresh, |
| background_thresh); |
| if (nr_dirty <= freerun) |
| break; |
| |
| if (unlikely(!writeback_in_progress(bdi))) |
| bdi_start_background_writeback(bdi); |
| |
| /* |
| * bdi_thresh is not treated as some limiting factor as |
| * dirty_thresh, due to reasons |
| * - in JBOD setup, bdi_thresh can fluctuate a lot |
| * - in a system with HDD and USB key, the USB key may somehow |
| * go into state (bdi_dirty >> bdi_thresh) either because |
| * bdi_dirty starts high, or because bdi_thresh drops low. |
| * In this case we don't want to hard throttle the USB key |
| * dirtiers for 100 seconds until bdi_dirty drops under |
| * bdi_thresh. Instead the auxiliary bdi control line in |
| * bdi_position_ratio() will let the dirtier task progress |
| * at some rate <= (write_bw / 2) for bringing down bdi_dirty. |
| */ |
| bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); |
| |
| /* |
| * In order to avoid the stacked BDI deadlock we need |
| * to ensure we accurately count the 'dirty' pages when |
| * the threshold is low. |
| * |
| * Otherwise it would be possible to get thresh+n pages |
| * reported dirty, even though there are thresh-m pages |
| * actually dirty; with m+n sitting in the percpu |
| * deltas. |
| */ |
| if (bdi_thresh < 2 * bdi_stat_error(bdi)) { |
| bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE); |
| bdi_dirty = bdi_reclaimable + |
| bdi_stat_sum(bdi, BDI_WRITEBACK); |
| } else { |
| bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE); |
| bdi_dirty = bdi_reclaimable + |
| bdi_stat(bdi, BDI_WRITEBACK); |
| } |
| |
| dirty_exceeded = (bdi_dirty > bdi_thresh) || |
| (nr_dirty > dirty_thresh); |
| if (dirty_exceeded && !bdi->dirty_exceeded) |
| bdi->dirty_exceeded = 1; |
| |
| bdi_update_bandwidth(bdi, dirty_thresh, background_thresh, |
| nr_dirty, bdi_thresh, bdi_dirty, |
| start_time); |
| |
| max_pause = bdi_max_pause(bdi, bdi_dirty); |
| |
| dirty_ratelimit = bdi->dirty_ratelimit; |
| pos_ratio = bdi_position_ratio(bdi, dirty_thresh, |
| background_thresh, nr_dirty, |
| bdi_thresh, bdi_dirty); |
| task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >> |
| RATELIMIT_CALC_SHIFT; |
| if (unlikely(task_ratelimit == 0)) { |
| pause = max_pause; |
| goto pause; |
| } |
| pause = HZ * pages_dirtied / task_ratelimit; |
| if (unlikely(pause <= 0)) { |
| trace_balance_dirty_pages(bdi, |
| dirty_thresh, |
| background_thresh, |
| nr_dirty, |
| bdi_thresh, |
| bdi_dirty, |
| dirty_ratelimit, |
| task_ratelimit, |
| pages_dirtied, |
| pause, |
| start_time); |
| pause = 1; /* avoid resetting nr_dirtied_pause below */ |
| break; |
| } |
| pause = min(pause, max_pause); |
| |
| pause: |
| trace_balance_dirty_pages(bdi, |
| dirty_thresh, |
| background_thresh, |
| nr_dirty, |
| bdi_thresh, |
| bdi_dirty, |
| dirty_ratelimit, |
| task_ratelimit, |
| pages_dirtied, |
| pause, |
| start_time); |
| __set_current_state(TASK_KILLABLE); |
| io_schedule_timeout(pause); |
| |
| /* |
| * This is typically equal to (nr_dirty < dirty_thresh) and can |
| * also keep "1000+ dd on a slow USB stick" under control. |
| */ |
| if (task_ratelimit) |
| break; |
| |
| /* |
| * In the case of an unresponding NFS server and the NFS dirty |
| * pages exceeds dirty_thresh, give the other good bdi's a pipe |
| * to go through, so that tasks on them still remain responsive. |
| * |
| * In theory 1 page is enough to keep the comsumer-producer |
| * pipe going: the flusher cleans 1 page => the task dirties 1 |
| * more page. However bdi_dirty has accounting errors. So use |
| * the larger and more IO friendly bdi_stat_error. |
| */ |
| if (bdi_dirty <= bdi_stat_error(bdi)) |
| break; |
| |
| if (fatal_signal_pending(current)) |
| break; |
| } |
| |
| if (!dirty_exceeded && bdi->dirty_exceeded) |
| bdi->dirty_exceeded = 0; |
| |
| current->nr_dirtied = 0; |
| if (pause == 0) { /* in freerun area */ |
| current->nr_dirtied_pause = |
| dirty_poll_interval(nr_dirty, dirty_thresh); |
| } else if (pause <= max_pause / 4 && |
| pages_dirtied >= current->nr_dirtied_pause) { |
| current->nr_dirtied_pause = clamp_val( |
| dirty_ratelimit * (max_pause / 2) / HZ, |
| pages_dirtied + pages_dirtied / 8, |
| pages_dirtied * 4); |
| } else if (pause >= max_pause) { |
| current->nr_dirtied_pause = 1 | clamp_val( |
| dirty_ratelimit * (max_pause / 2) / HZ, |
| pages_dirtied / 4, |
| pages_dirtied - pages_dirtied / 8); |
| } |
| |
| if (writeback_in_progress(bdi)) |
| return; |
| |
| /* |
| * In laptop mode, we wait until hitting the higher threshold before |
| * starting background writeout, and then write out all the way down |
| * to the lower threshold. So slow writers cause minimal disk activity. |
| * |
| * In normal mode, we start background writeout at the lower |
| * background_thresh, to keep the amount of dirty memory low. |
| */ |
| if (laptop_mode) |
| return; |
| |
| if (nr_reclaimable > background_thresh) |
| bdi_start_background_writeback(bdi); |
| } |
| |
| void set_page_dirty_balance(struct page *page, int page_mkwrite) |
| { |
| if (set_page_dirty(page) || page_mkwrite) { |
| struct address_space *mapping = page_mapping(page); |
| |
| if (mapping) |
| balance_dirty_pages_ratelimited(mapping); |
| } |
| } |
| |
| static DEFINE_PER_CPU(int, bdp_ratelimits); |
| |
| /** |
| * balance_dirty_pages_ratelimited_nr - balance dirty memory state |
| * @mapping: address_space which was dirtied |
| * @nr_pages_dirtied: number of pages which the caller has just dirtied |
| * |
| * Processes which are dirtying memory should call in here once for each page |
| * which was newly dirtied. The function will periodically check the system's |
| * dirty state and will initiate writeback if needed. |
| * |
| * On really big machines, get_writeback_state is expensive, so try to avoid |
| * calling it too often (ratelimiting). But once we're over the dirty memory |
| * limit we decrease the ratelimiting by a lot, to prevent individual processes |
| * from overshooting the limit by (ratelimit_pages) each. |
| */ |
| void balance_dirty_pages_ratelimited_nr(struct address_space *mapping, |
| unsigned long nr_pages_dirtied) |
| { |
| struct backing_dev_info *bdi = mapping->backing_dev_info; |
| int ratelimit; |
| int *p; |
| |
| if (!bdi_cap_account_dirty(bdi)) |
| return; |
| |
| ratelimit = current->nr_dirtied_pause; |
| if (bdi->dirty_exceeded) |
| ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10)); |
| |
| current->nr_dirtied += nr_pages_dirtied; |
| |
| preempt_disable(); |
| /* |
| * This prevents one CPU to accumulate too many dirtied pages without |
| * calling into balance_dirty_pages(), which can happen when there are |
| * 1000+ tasks, all of them start dirtying pages at exactly the same |
| * time, hence all honoured too large initial task->nr_dirtied_pause. |
| */ |
| p = &__get_cpu_var(bdp_ratelimits); |
| if (unlikely(current->nr_dirtied >= ratelimit)) |
| *p = 0; |
| else { |
| *p += nr_pages_dirtied; |
| if (unlikely(*p >= ratelimit_pages)) { |
| *p = 0; |
| ratelimit = 0; |
| } |
| } |
| preempt_enable(); |
| |
| if (unlikely(current->nr_dirtied >= ratelimit)) |
| balance_dirty_pages(mapping, current->nr_dirtied); |
| } |
| EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); |
| |
| void throttle_vm_writeout(gfp_t gfp_mask) |
| { |
| unsigned long background_thresh; |
| unsigned long dirty_thresh; |
| |
| for ( ; ; ) { |
| global_dirty_limits(&background_thresh, &dirty_thresh); |
| |
| /* |
| * Boost the allowable dirty threshold a bit for page |
| * allocators so they don't get DoS'ed by heavy writers |
| */ |
| dirty_thresh += dirty_thresh / 10; /* wheeee... */ |
| |
| if (global_page_state(NR_UNSTABLE_NFS) + |
| global_page_state(NR_WRITEBACK) <= dirty_thresh) |
| break; |
| congestion_wait(BLK_RW_ASYNC, HZ/10); |
| |
| /* |
| * The caller might hold locks which can prevent IO completion |
| * or progress in the filesystem. So we cannot just sit here |
| * waiting for IO to complete. |
| */ |
| if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) |
| break; |
| } |
| } |
| |
| /* |
| * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs |
| */ |
| int dirty_writeback_centisecs_handler(ctl_table *table, int write, |
| void __user *buffer, size_t *length, loff_t *ppos) |
| { |
| proc_dointvec(table, write, buffer, length, ppos); |
| bdi_arm_supers_timer(); |
| return 0; |
| } |
| |
| #ifdef CONFIG_BLOCK |
| void laptop_mode_timer_fn(unsigned long data) |
| { |
| struct request_queue *q = (struct request_queue *)data; |
| int nr_pages = global_page_state(NR_FILE_DIRTY) + |
| global_page_state(NR_UNSTABLE_NFS); |
| |
| /* |
| * We want to write everything out, not just down to the dirty |
| * threshold |
| */ |
| if (bdi_has_dirty_io(&q->backing_dev_info)) |
| bdi_start_writeback(&q->backing_dev_info, nr_pages, |
| WB_REASON_LAPTOP_TIMER); |
| } |
| |
| /* |
| * We've spun up the disk and we're in laptop mode: schedule writeback |
| * of all dirty data a few seconds from now. If the flush is already scheduled |
| * then push it back - the user is still using the disk. |
| */ |
| void laptop_io_completion(struct backing_dev_info *info) |
| { |
| mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode); |
| } |
| |
| /* |
| * We're in laptop mode and we've just synced. The sync's writes will have |
| * caused another writeback to be scheduled by laptop_io_completion. |
| * Nothing needs to be written back anymore, so we unschedule the writeback. |
| */ |
| void laptop_sync_completion(void) |
| { |
| struct backing_dev_info *bdi; |
| |
| rcu_read_lock(); |
| |
| list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) |
| del_timer(&bdi->laptop_mode_wb_timer); |
| |
| rcu_read_unlock(); |
| } |
| #endif |
| |
| /* |
| * If ratelimit_pages is too high then we can get into dirty-data overload |
| * if a large number of processes all perform writes at the same time. |
| * If it is too low then SMP machines will call the (expensive) |
| * get_writeback_state too often. |
| * |
| * Here we set ratelimit_pages to a level which ensures that when all CPUs are |
| * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory |
| * thresholds. |
| */ |
| |
| void writeback_set_ratelimit(void) |
| { |
| unsigned long background_thresh; |
| unsigned long dirty_thresh; |
| global_dirty_limits(&background_thresh, &dirty_thresh); |
| ratelimit_pages = dirty_thresh / (num_online_cpus() * 32); |
| if (ratelimit_pages < 16) |
| ratelimit_pages = 16; |
| } |
| |
| static int __cpuinit |
| ratelimit_handler(struct notifier_block *self, unsigned long u, void *v) |
| { |
| writeback_set_ratelimit(); |
| return NOTIFY_DONE; |
| } |
| |
| static struct notifier_block __cpuinitdata ratelimit_nb = { |
| .notifier_call = ratelimit_handler, |
| .next = NULL, |
| }; |
| |
| /* |
| * Called early on to tune the page writeback dirty limits. |
| * |
| * We used to scale dirty pages according to how total memory |
| * related to pages that could be allocated for buffers (by |
| * comparing nr_free_buffer_pages() to vm_total_pages. |
| * |
| * However, that was when we used "dirty_ratio" to scale with |
| * all memory, and we don't do that any more. "dirty_ratio" |
| * is now applied to total non-HIGHPAGE memory (by subtracting |
| * totalhigh_pages from vm_total_pages), and as such we can't |
| * get into the old insane situation any more where we had |
| * large amounts of dirty pages compared to a small amount of |
| * non-HIGHMEM memory. |
| * |
| * But we might still want to scale the dirty_ratio by how |
| * much memory the box has.. |
| */ |
| void __init page_writeback_init(void) |
| { |
| int shift; |
| |
| writeback_set_ratelimit(); |
| register_cpu_notifier(&ratelimit_nb); |
| |
| shift = calc_period_shift(); |
| prop_descriptor_init(&vm_completions, shift); |
| } |
| |
| /** |
| * tag_pages_for_writeback - tag pages to be written by write_cache_pages |
| * @mapping: address space structure to write |
| * @start: starting page index |
| * @end: ending page index (inclusive) |
| * |
| * This function scans the page range from @start to @end (inclusive) and tags |
| * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is |
| * that write_cache_pages (or whoever calls this function) will then use |
| * TOWRITE tag to identify pages eligible for writeback. This mechanism is |
| * used to avoid livelocking of writeback by a process steadily creating new |
| * dirty pages in the file (thus it is important for this function to be quick |
| * so that it can tag pages faster than a dirtying process can create them). |
| */ |
| /* |
| * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency. |
| */ |
| void tag_pages_for_writeback(struct address_space *mapping, |
| pgoff_t start, pgoff_t end) |
| { |
| #define WRITEBACK_TAG_BATCH 4096 |
| unsigned long tagged; |
| |
| do { |
| spin_lock_irq(&mapping->tree_lock); |
| tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree, |
| &start, end, WRITEBACK_TAG_BATCH, |
| PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE); |
| spin_unlock_irq(&mapping->tree_lock); |
| WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH); |
| cond_resched(); |
| /* We check 'start' to handle wrapping when end == ~0UL */ |
| } while (tagged >= WRITEBACK_TAG_BATCH && start); |
| } |
| EXPORT_SYMBOL(tag_pages_for_writeback); |
| |
| /** |
| * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. |
| * @mapping: address space structure to write |
| * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
| * @writepage: function called for each page |
| * @data: data passed to writepage function |
| * |
| * If a page is already under I/O, write_cache_pages() skips it, even |
| * if it's dirty. This is desirable behaviour for memory-cleaning writeback, |
| * but it is INCORRECT for data-integrity system calls such as fsync(). fsync() |
| * and msync() need to guarantee that all the data which was dirty at the time |
| * the call was made get new I/O started against them. If wbc->sync_mode is |
| * WB_SYNC_ALL then we were called for data integrity and we must wait for |
| * existing IO to complete. |
| * |
| * To avoid livelocks (when other process dirties new pages), we first tag |
| * pages which should be written back with TOWRITE tag and only then start |
| * writing them. For data-integrity sync we have to be careful so that we do |
| * not miss some pages (e.g., because some other process has cleared TOWRITE |
| * tag we set). The rule we follow is that TOWRITE tag can be cleared only |
| * by the process clearing the DIRTY tag (and submitting the page for IO). |
| */ |
| int write_cache_pages(struct address_space *mapping, |
| struct writeback_control *wbc, writepage_t writepage, |
| void *data) |
| { |
| int ret = 0; |
| int done = 0; |
| struct pagevec pvec; |
| int nr_pages; |
| pgoff_t uninitialized_var(writeback_index); |
| pgoff_t index; |
| pgoff_t end; /* Inclusive */ |
| pgoff_t done_index; |
| int cycled; |
| int range_whole = 0; |
| int tag; |
| |
| pagevec_init(&pvec, 0); |
| if (wbc->range_cyclic) { |
| writeback_index = mapping->writeback_index; /* prev offset */ |
| index = writeback_index; |
| if (index == 0) |
| cycled = 1; |
| else |
| cycled = 0; |
| end = -1; |
| } else { |
| index = wbc->range_start >> PAGE_CACHE_SHIFT; |
| end = wbc->range_end >> PAGE_CACHE_SHIFT; |
| if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) |
| range_whole = 1; |
| cycled = 1; /* ignore range_cyclic tests */ |
| } |
| if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
| tag = PAGECACHE_TAG_TOWRITE; |
| else |
| tag = PAGECACHE_TAG_DIRTY; |
| retry: |
| if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) |
| tag_pages_for_writeback(mapping, index, end); |
| done_index = index; |
| while (!done && (index <= end)) { |
| int i; |
| |
| nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, |
| min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); |
| if (nr_pages == 0) |
| break; |
| |
| for (i = 0; i < nr_pages; i++) { |
| struct page *page = pvec.pages[i]; |
| |
| /* |
| * At this point, the page may be truncated or |
| * invalidated (changing page->mapping to NULL), or |
| * even swizzled back from swapper_space to tmpfs file |
| * mapping. However, page->index will not change |
| * because we have a reference on the page. |
| */ |
| if (page->index > end) { |
| /* |
| * can't be range_cyclic (1st pass) because |
| * end == -1 in that case. |
| */ |
| done = 1; |
| break; |
| } |
| |
| done_index = page->index; |
| |
| lock_page(page); |
| |
| /* |
| * Page truncated or invalidated. We can freely skip it |
| * then, even for data integrity operations: the page |
| * has disappeared concurrently, so there could be no |
| * real expectation of this data interity operation |
| * even if there is now a new, dirty page at the same |
| * pagecache address. |
| */ |
| if (unlikely(page->mapping != mapping)) { |
| continue_unlock: |
| unlock_page(page); |
| continue; |
| } |
| |
| if (!PageDirty(page)) { |
| /* someone wrote it for us */ |
| goto continue_unlock; |
| } |
| |
| if (PageWriteback(page)) { |
| if (wbc->sync_mode != WB_SYNC_NONE) |
| wait_on_page_writeback(page); |
| else |
| goto continue_unlock; |
| } |
| |
| BUG_ON(PageWriteback(page)); |
| if (!clear_page_dirty_for_io(page)) |
| goto continue_unlock; |
| |
| trace_wbc_writepage(wbc, mapping->backing_dev_info); |
| ret = (*writepage)(page, wbc, data); |
| if (unlikely(ret)) { |
| if (ret == AOP_WRITEPAGE_ACTIVATE) { |
| unlock_page(page); |
| ret = 0; |
| } else { |
| /* |
| * done_index is set past this page, |
| * so media errors will not choke |
| * background writeout for the entire |
| * file. This has consequences for |
| * range_cyclic semantics (ie. it may |
| * not be suitable for data integrity |
| * writeout). |
| */ |
| done_index = page->index + 1; |
| done = 1; |
| break; |
| } |
| } |
| |
| /* |
| * We stop writing back only if we are not doing |
| * integrity sync. In case of integrity sync we have to |
| * keep going until we have written all the pages |
| * we tagged for writeback prior to entering this loop. |
| */ |
| if (--wbc->nr_to_write <= 0 && |
| wbc->sync_mode == WB_SYNC_NONE) { |
| done = 1; |
| break; |
| } |
| } |
| pagevec_release(&pvec); |
| cond_resched(); |
| } |
| if (!cycled && !done) { |
| /* |
| * range_cyclic: |
| * We hit the last page and there is more work to be done: wrap |
| * back to the start of the file |
| */ |
| cycled = 1; |
| index = 0; |
| end = writeback_index - 1; |
| goto retry; |
| } |
| if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0)) |
| mapping->writeback_index = done_index; |
| |
| return ret; |
| } |
| EXPORT_SYMBOL(write_cache_pages); |
| |
| /* |
| * Function used by generic_writepages to call the real writepage |
| * function and set the mapping flags on error |
| */ |
| static int __writepage(struct page *page, struct writeback_control *wbc, |
| void *data) |
| { |
| struct address_space *mapping = data; |
| int ret = mapping->a_ops->writepage(page, wbc); |
| mapping_set_error(mapping, ret); |
| return ret; |
| } |
| |
| /** |
| * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them. |
| * @mapping: address space structure to write |
| * @wbc: subtract the number of written pages from *@wbc->nr_to_write |
| * |
| * This is a library function, which implements the writepages() |
| * address_space_operation. |
| */ |
| int generic_writepages(struct address_space *mapping, |
| struct writeback_control *wbc) |
| { |
| struct blk_plug plug; |
| int ret; |
| |
| /* deal with chardevs and other special file */ |
| if (!mapping->a_ops->writepage) |
| return 0; |
| |
| blk_start_plug(&plug); |
| ret = write_cache_pages(mapping, wbc, __writepage, mapping); |
| blk_finish_plug(&plug); |
| return ret; |
| } |
| |
| EXPORT_SYMBOL(generic_writepages); |
| |
| int do_writepages(struct address_space *mapping, struct writeback_control *wbc) |
| { |
| int ret; |
| |
| if (wbc->nr_to_write <= 0) |
| return 0; |
| if (mapping->a_ops->writepages) |
| ret = mapping->a_ops->writepages(mapping, wbc); |
| else |
| ret = generic_writepages(mapping, wbc); |
| return ret; |
| } |
| |
| /** |
| * write_one_page - write out a single page and optionally wait on I/O |
| * @page: the page to write |
| * @wait: if true, wait on writeout |
| * |
| * The page must be locked by the caller and will be unlocked upon return. |
| * |
| * write_one_page() returns a negative error code if I/O failed. |
| */ |
| int write_one_page(struct page *page, int wait) |
| { |
| struct address_space *mapping = page->mapping; |
| int ret = 0; |
| struct writeback_control wbc = { |
| .sync_mode = WB_SYNC_ALL, |
| .nr_to_write = 1, |
| }; |
| |
| BUG_ON(!PageLocked(page)); |
| |
| if (wait) |
| wait_on_page_writeback(page); |
| |
| if (clear_page_dirty_for_io(page)) { |
| page_cache_get(page); |
| ret = mapping->a_ops->writepage(page, &wbc); |
| if (ret == 0 && wait) { |
| wait_on_page_writeback(page); |
| if (PageError(page)) |
| ret = -EIO; |
| } |
| page_cache_release(page); |
| } else { |
| unlock_page(page); |
| } |
| return ret; |
| } |
| EXPORT_SYMBOL(write_one_page); |
| |
| /* |
| * For address_spaces which do not use buffers nor write back. |
| */ |
| int __set_page_dirty_no_writeback(struct page *page) |
| { |
| if (!PageDirty(page)) |
| return !TestSetPageDirty(page); |
| return 0; |
| } |
| |
| /* |
| * Helper function for set_page_dirty family. |
| * NOTE: This relies on being atomic wrt interrupts. |
| */ |
| void account_page_dirtied(struct page *page, struct address_space *mapping) |
| { |
| if (mapping_cap_account_dirty(mapping)) { |
| __inc_zone_page_state(page, NR_FILE_DIRTY); |
| __inc_zone_page_state(page, NR_DIRTIED); |
| __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); |
| __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); |
| task_io_account_write(PAGE_CACHE_SIZE); |
| } |
| } |
| EXPORT_SYMBOL(account_page_dirtied); |
| |
| /* |
| * Helper function for set_page_writeback family. |
| * NOTE: Unlike account_page_dirtied this does not rely on being atomic |
| * wrt interrupts. |
| */ |
| void account_page_writeback(struct page *page) |
| { |
| inc_zone_page_state(page, NR_WRITEBACK); |
| } |
| EXPORT_SYMBOL(account_page_writeback); |
| |
| /* |
| * For address_spaces which do not use buffers. Just tag the page as dirty in |
| * its radix tree. |
| * |
| * This is also used when a single buffer is being dirtied: we want to set the |
| * page dirty in that case, but not all the buffers. This is a "bottom-up" |
| * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying. |
| * |
| * Most callers have locked the page, which pins the address_space in memory. |
| * But zap_pte_range() does not lock the page, however in that case the |
| * mapping is pinned by the vma's ->vm_file reference. |
| * |
| * We take care to handle the case where the page was truncated from the |
| * mapping by re-checking page_mapping() inside tree_lock. |
| */ |
| int __set_page_dirty_nobuffers(struct page *page) |
| { |
| if (!TestSetPageDirty(page)) { |
| struct address_space *mapping = page_mapping(page); |
| struct address_space *mapping2; |
| |
| if (!mapping) |
| return 1; |
| |
| spin_lock_irq(&mapping->tree_lock); |
| mapping2 = page_mapping(page); |
| if (mapping2) { /* Race with truncate? */ |
| BUG_ON(mapping2 != mapping); |
| WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); |
| account_page_dirtied(page, mapping); |
| radix_tree_tag_set(&mapping->page_tree, |
| page_index(page), PAGECACHE_TAG_DIRTY); |
| } |
| spin_unlock_irq(&mapping->tree_lock); |
| if (mapping->host) { |
| /* !PageAnon && !swapper_space */ |
| __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); |
| } |
| return 1; |
| } |
| return 0; |
| } |
| EXPORT_SYMBOL(__set_page_dirty_nobuffers); |
| |
| /* |
| * When a writepage implementation decides that it doesn't want to write this |
| * page for some reason, it should redirty the locked page via |
| * redirty_page_for_writepage() and it should then unlock the page and return 0 |
| */ |
| int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) |
| { |
| wbc->pages_skipped++; |
| return __set_page_dirty_nobuffers(page); |
| } |
| EXPORT_SYMBOL(redirty_page_for_writepage); |
| |
| /* |
| * Dirty a page. |
| * |
| * For pages with a mapping this should be done under the page lock |
| * for the benefit of asynchronous memory errors who prefer a consistent |
| * dirty state. This rule can be broken in some special cases, |
| * but should be better not to. |
| * |
| * If the mapping doesn't provide a set_page_dirty a_op, then |
| * just fall through and assume that it wants buffer_heads. |
| */ |
| int set_page_dirty(struct page *page) |
| { |
| struct address_space *mapping = page_mapping(page); |
| |
| if (likely(mapping)) { |
| int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; |
| /* |
| * readahead/lru_deactivate_page could remain |
| * PG_readahead/PG_reclaim due to race with end_page_writeback |
| * About readahead, if the page is written, the flags would be |
| * reset. So no problem. |
| * About lru_deactivate_page, if the page is redirty, the flag |
| * will be reset. So no problem. but if the page is used by readahead |
| * it will confuse readahead and make it restart the size rampup |
| * process. But it's a trivial problem. |
| */ |
| ClearPageReclaim(page); |
| #ifdef CONFIG_BLOCK |
| if (!spd) |
| spd = __set_page_dirty_buffers; |
| #endif |
| return (*spd)(page); |
| } |
| if (!PageDirty(page)) { |
| if (!TestSetPageDirty(page)) |
| return 1; |
| } |
| return 0; |
| } |
| EXPORT_SYMBOL(set_page_dirty); |
| |
| /* |
| * set_page_dirty() is racy if the caller has no reference against |
| * page->mapping->host, and if the page is unlocked. This is because another |
| * CPU could truncate the page off the mapping and then free the mapping. |
| * |
| * Usually, the page _is_ locked, or the caller is a user-space process which |
| * holds a reference on the inode by having an open file. |
| * |
| * In other cases, the page should be locked before running set_page_dirty(). |
| */ |
| int set_page_dirty_lock(struct page *page) |
| { |
| int ret; |
| |
| lock_page(page); |
| ret = set_page_dirty(page); |
| unlock_page(page); |
| return ret; |
| } |
| EXPORT_SYMBOL(set_page_dirty_lock); |
| |
| /* |
| * Clear a page's dirty flag, while caring for dirty memory accounting. |
| * Returns true if the page was previously dirty. |
| * |
| * This is for preparing to put the page under writeout. We leave the page |
| * tagged as dirty in the radix tree so that a concurrent write-for-sync |
| * can discover it via a PAGECACHE_TAG_DIRTY walk. The ->writepage |
| * implementation will run either set_page_writeback() or set_page_dirty(), |
| * at which stage we bring the page's dirty flag and radix-tree dirty tag |
| * back into sync. |
| * |
| * This incoherency between the page's dirty flag and radix-tree tag is |
| * unfortunate, but it only exists while the page is locked. |
| */ |
| int clear_page_dirty_for_io(struct page *page) |
| { |
| struct address_space *mapping = page_mapping(page); |
| |
| BUG_ON(!PageLocked(page)); |
| |
| if (mapping && mapping_cap_account_dirty(mapping)) { |
| /* |
| * Yes, Virginia, this is indeed insane. |
| * |
| * We use this sequence to make sure that |
| * (a) we account for dirty stats properly |
| * (b) we tell the low-level filesystem to |
| * mark the whole page dirty if it was |
| * dirty in a pagetable. Only to then |
| * (c) clean the page again and return 1 to |
| * cause the writeback. |
| * |
| * This way we avoid all nasty races with the |
| * dirty bit in multiple places and clearing |
| * them concurrently from different threads. |
| * |
| * Note! Normally the "set_page_dirty(page)" |
| * has no effect on the actual dirty bit - since |
| * that will already usually be set. But we |
| * need the side effects, and it can help us |
| * avoid races. |
| * |
| * We basically use the page "master dirty bit" |
| * as a serialization point for all the different |
| * threads doing their things. |
| */ |
| if (page_mkclean(page)) |
| set_page_dirty(page); |
| /* |
| * We carefully synchronise fault handlers against |
| * installing a dirty pte and marking the page dirty |
| * at this point. We do this by having them hold the |
| * page lock at some point after installing their |
| * pte, but before marking the page dirty. |
| * Pages are always locked coming in here, so we get |
| * the desired exclusion. See mm/memory.c:do_wp_page() |
| * for more comments. |
| */ |
| if (TestClearPageDirty(page)) { |
| dec_zone_page_state(page, NR_FILE_DIRTY); |
| dec_bdi_stat(mapping->backing_dev_info, |
| BDI_RECLAIMABLE); |
| return 1; |
| } |
| return 0; |
| } |
| return TestClearPageDirty(page); |
| } |
| EXPORT_SYMBOL(clear_page_dirty_for_io); |
| |
| int test_clear_page_writeback(struct page *page) |
| { |
| struct address_space *mapping = page_mapping(page); |
| int ret; |
| |
| if (mapping) { |
| struct backing_dev_info *bdi = mapping->backing_dev_info; |
| unsigned long flags; |
| |
| spin_lock_irqsave(&mapping->tree_lock, flags); |
| ret = TestClearPageWriteback(page); |
| if (ret) { |
| radix_tree_tag_clear(&mapping->page_tree, |
| page_index(page), |
| PAGECACHE_TAG_WRITEBACK); |
| if (bdi_cap_account_writeback(bdi)) { |
| __dec_bdi_stat(bdi, BDI_WRITEBACK); |
| __bdi_writeout_inc(bdi); |
| } |
| } |
| spin_unlock_irqrestore(&mapping->tree_lock, flags); |
| } else { |
| ret = TestClearPageWriteback(page); |
| } |
| if (ret) { |
| dec_zone_page_state(page, NR_WRITEBACK); |
| inc_zone_page_state(page, NR_WRITTEN); |
| } |
| return ret; |
| } |
| |
| int test_set_page_writeback(struct page *page) |
| { |
| struct address_space *mapping = page_mapping(page); |
| int ret; |
| |
| if (mapping) { |
| struct backing_dev_info *bdi = mapping->backing_dev_info; |
| unsigned long flags; |
| |
| spin_lock_irqsave(&mapping->tree_lock, flags); |
| ret = TestSetPageWriteback(page); |
| if (!ret) { |
| radix_tree_tag_set(&mapping->page_tree, |
| page_index(page), |
| PAGECACHE_TAG_WRITEBACK); |
| if (bdi_cap_account_writeback(bdi)) |
| __inc_bdi_stat(bdi, BDI_WRITEBACK); |
| } |
| if (!PageDirty(page)) |
| radix_tree_tag_clear(&mapping->page_tree, |
| page_index(page), |
| PAGECACHE_TAG_DIRTY); |
| radix_tree_tag_clear(&mapping->page_tree, |
| page_index(page), |
| PAGECACHE_TAG_TOWRITE); |
| spin_unlock_irqrestore(&mapping->tree_lock, flags); |
| } else { |
| ret = TestSetPageWriteback(page); |
| } |
| if (!ret) |
| account_page_writeback(page); |
| return ret; |
| |
| } |
| EXPORT_SYMBOL(test_set_page_writeback); |
| |
| /* |
| * Return true if any of the pages in the mapping are marked with the |
| * passed tag. |
| */ |
| int mapping_tagged(struct address_space *mapping, int tag) |
| { |
| return radix_tree_tagged(&mapping->page_tree, tag); |
| } |
| EXPORT_SYMBOL(mapping_tagged); |