Merge branch 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux
* 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux: writeback: Add a 'reason' to wb_writeback_work writeback: send work item to queue_io, move_expired_inodes writeback: trace event balance_dirty_pages writeback: trace event bdi_dirty_ratelimit writeback: fix ppc compile warnings on do_div(long long, unsigned long) writeback: per-bdi background threshold writeback: dirty position control - bdi reserve area writeback: control dirty pause time writeback: limit max dirty pause time writeback: IO-less balance_dirty_pages() writeback: per task dirty rate limit writeback: stabilize bdi->dirty_ratelimit writeback: dirty rate control writeback: add bg_threshold parameter to __bdi_update_bandwidth() writeback: dirty position control writeback: account per-bdi accumulated dirtied pages
This commit is contained in:
Linus Torvalds
+553
-153
@@ -46,26 +46,14 @@
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*/
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#define BANDWIDTH_INTERVAL max(HZ/5, 1)
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#define RATELIMIT_CALC_SHIFT 10
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/*
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* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
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* will look to see if it needs to force writeback or throttling.
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*/
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static long ratelimit_pages = 32;
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/*
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* When balance_dirty_pages decides that the caller needs to perform some
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* non-background writeback, this is how many pages it will attempt to write.
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* It should be somewhat larger than dirtied pages to ensure that reasonably
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* large amounts of I/O are submitted.
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*/
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static inline long sync_writeback_pages(unsigned long dirtied)
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{
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if (dirtied < ratelimit_pages)
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dirtied = ratelimit_pages;
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return dirtied + dirtied / 2;
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}
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/* The following parameters are exported via /proc/sys/vm */
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/*
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@@ -167,6 +155,8 @@ static void update_completion_period(void)
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int shift = calc_period_shift();
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prop_change_shift(&vm_completions, shift);
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prop_change_shift(&vm_dirties, shift);
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writeback_set_ratelimit();
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}
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int dirty_background_ratio_handler(struct ctl_table *table, int write,
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@@ -260,50 +250,6 @@ static void bdi_writeout_fraction(struct backing_dev_info *bdi,
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numerator, denominator);
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}
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static inline void task_dirties_fraction(struct task_struct *tsk,
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long *numerator, long *denominator)
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{
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prop_fraction_single(&vm_dirties, &tsk->dirties,
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numerator, denominator);
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}
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/*
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* task_dirty_limit - scale down dirty throttling threshold for one task
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*
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* task specific dirty limit:
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*
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* dirty -= (dirty/8) * p_{t}
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*
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* To protect light/slow dirtying tasks from heavier/fast ones, we start
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* throttling individual tasks before reaching the bdi dirty limit.
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* Relatively low thresholds will be allocated to heavy dirtiers. So when
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* dirty pages grow large, heavy dirtiers will be throttled first, which will
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* effectively curb the growth of dirty pages. Light dirtiers with high enough
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* dirty threshold may never get throttled.
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*/
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#define TASK_LIMIT_FRACTION 8
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static unsigned long task_dirty_limit(struct task_struct *tsk,
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unsigned long bdi_dirty)
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{
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long numerator, denominator;
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unsigned long dirty = bdi_dirty;
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u64 inv = dirty / TASK_LIMIT_FRACTION;
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task_dirties_fraction(tsk, &numerator, &denominator);
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inv *= numerator;
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do_div(inv, denominator);
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dirty -= inv;
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return max(dirty, bdi_dirty/2);
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}
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/* Minimum limit for any task */
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static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
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{
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return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
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}
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/*
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* bdi_min_ratio keeps the sum of the minimum dirty shares of all
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* registered backing devices, which, for obvious reasons, can not
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@@ -413,6 +359,12 @@ unsigned long determine_dirtyable_memory(void)
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return x + 1; /* Ensure that we never return 0 */
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}
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static unsigned long dirty_freerun_ceiling(unsigned long thresh,
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unsigned long bg_thresh)
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{
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return (thresh + bg_thresh) / 2;
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}
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static unsigned long hard_dirty_limit(unsigned long thresh)
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{
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return max(thresh, global_dirty_limit);
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@@ -497,6 +449,198 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
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return bdi_dirty;
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}
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/*
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* Dirty position control.
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*
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* (o) global/bdi setpoints
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*
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* We want the dirty pages be balanced around the global/bdi setpoints.
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* When the number of dirty pages is higher/lower than the setpoint, the
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* dirty position control ratio (and hence task dirty ratelimit) will be
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* decreased/increased to bring the dirty pages back to the setpoint.
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*
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* pos_ratio = 1 << RATELIMIT_CALC_SHIFT
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*
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* if (dirty < setpoint) scale up pos_ratio
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* if (dirty > setpoint) scale down pos_ratio
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*
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* if (bdi_dirty < bdi_setpoint) scale up pos_ratio
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* if (bdi_dirty > bdi_setpoint) scale down pos_ratio
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*
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* task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
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*
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* (o) global control line
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*
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* ^ pos_ratio
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* |
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* | |<===== global dirty control scope ======>|
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* 2.0 .............*
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* | .*
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* 1.0 ................................*
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* | . . *
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* | . . *
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* | . . *
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* | . . *
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* | . . *
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* 0 +------------.------------------.----------------------*------------->
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* freerun^ setpoint^ limit^ dirty pages
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*
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* (o) bdi control line
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*
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* ^ pos_ratio
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* |
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* | *
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* | *
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* | *
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* | *
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* | * |<=========== span ============>|
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* 1.0 .......................*
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* | . *
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* 1/4 ...............................................* * * * * * * * * * * *
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* | . .
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* | . .
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* | . .
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* 0 +----------------------.-------------------------------.------------->
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* bdi_setpoint^ x_intercept^
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*
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* The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
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* be smoothly throttled down to normal if it starts high in situations like
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* - start writing to a slow SD card and a fast disk at the same time. The SD
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* card's bdi_dirty may rush to many times higher than bdi_setpoint.
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* - the bdi dirty thresh drops quickly due to change of JBOD workload
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*/
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static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
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unsigned long thresh,
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unsigned long bg_thresh,
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unsigned long dirty,
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unsigned long bdi_thresh,
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unsigned long bdi_dirty)
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{
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unsigned long write_bw = bdi->avg_write_bandwidth;
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unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
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unsigned long limit = hard_dirty_limit(thresh);
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unsigned long x_intercept;
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unsigned long setpoint; /* dirty pages' target balance point */
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unsigned long bdi_setpoint;
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unsigned long span;
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long long pos_ratio; /* for scaling up/down the rate limit */
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long x;
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if (unlikely(dirty >= limit))
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return 0;
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/*
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* global setpoint
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*
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* setpoint - dirty 3
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* f(dirty) := 1.0 + (----------------)
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* limit - setpoint
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*
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* it's a 3rd order polynomial that subjects to
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*
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* (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
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* (2) f(setpoint) = 1.0 => the balance point
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* (3) f(limit) = 0 => the hard limit
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* (4) df/dx <= 0 => negative feedback control
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* (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
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* => fast response on large errors; small oscillation near setpoint
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*/
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setpoint = (freerun + limit) / 2;
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x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
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limit - setpoint + 1);
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pos_ratio = x;
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pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
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pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
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pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
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/*
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* We have computed basic pos_ratio above based on global situation. If
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* the bdi is over/under its share of dirty pages, we want to scale
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* pos_ratio further down/up. That is done by the following mechanism.
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*/
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/*
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* bdi setpoint
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*
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* f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
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*
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* x_intercept - bdi_dirty
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* := --------------------------
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* x_intercept - bdi_setpoint
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*
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* The main bdi control line is a linear function that subjects to
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*
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* (1) f(bdi_setpoint) = 1.0
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* (2) k = - 1 / (8 * write_bw) (in single bdi case)
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* or equally: x_intercept = bdi_setpoint + 8 * write_bw
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*
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* For single bdi case, the dirty pages are observed to fluctuate
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* regularly within range
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* [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
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* for various filesystems, where (2) can yield in a reasonable 12.5%
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* fluctuation range for pos_ratio.
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*
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* For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
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* own size, so move the slope over accordingly and choose a slope that
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* yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
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*/
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if (unlikely(bdi_thresh > thresh))
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bdi_thresh = thresh;
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bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
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/*
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* scale global setpoint to bdi's:
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* bdi_setpoint = setpoint * bdi_thresh / thresh
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*/
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x = div_u64((u64)bdi_thresh << 16, thresh + 1);
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bdi_setpoint = setpoint * (u64)x >> 16;
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/*
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* Use span=(8*write_bw) in single bdi case as indicated by
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* (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
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*
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* bdi_thresh thresh - bdi_thresh
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* span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
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* thresh thresh
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*/
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span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
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x_intercept = bdi_setpoint + span;
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if (bdi_dirty < x_intercept - span / 4) {
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pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
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x_intercept - bdi_setpoint + 1);
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} else
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pos_ratio /= 4;
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/*
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* bdi reserve area, safeguard against dirty pool underrun and disk idle
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* It may push the desired control point of global dirty pages higher
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* than setpoint.
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*/
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x_intercept = bdi_thresh / 2;
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if (bdi_dirty < x_intercept) {
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if (bdi_dirty > x_intercept / 8)
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pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
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else
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pos_ratio *= 8;
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}
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return pos_ratio;
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}
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static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
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unsigned long elapsed,
|
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unsigned long written)
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@@ -593,8 +737,153 @@ static void global_update_bandwidth(unsigned long thresh,
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||||
spin_unlock(&dirty_lock);
|
||||
}
|
||||
|
||||
/*
|
||||
* Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
|
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*
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* Normal bdi tasks will be curbed at or below it in long term.
|
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* Obviously it should be around (write_bw / N) when there are N dd tasks.
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*/
|
||||
static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
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unsigned long thresh,
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unsigned long bg_thresh,
|
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unsigned long dirty,
|
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unsigned long bdi_thresh,
|
||||
unsigned long bdi_dirty,
|
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unsigned long dirtied,
|
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unsigned long elapsed)
|
||||
{
|
||||
unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
|
||||
unsigned long limit = hard_dirty_limit(thresh);
|
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unsigned long setpoint = (freerun + limit) / 2;
|
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unsigned long write_bw = bdi->avg_write_bandwidth;
|
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unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
|
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unsigned long dirty_rate;
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||||
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;
|
||||
|
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pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
|
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bdi_thresh, bdi_dirty);
|
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/*
|
||||
* task_ratelimit reflects each dd's dirty rate for the past 200ms.
|
||||
*/
|
||||
task_ratelimit = (u64)dirty_ratelimit *
|
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pos_ratio >> RATELIMIT_CALC_SHIFT;
|
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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)
|
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* yielding
|
||||
* dirty_rate = N * task_ratelimit = write_bw (6)
|
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* 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,
|
||||
@@ -602,6 +891,7 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi,
|
||||
{
|
||||
unsigned long now = jiffies;
|
||||
unsigned long elapsed = now - bdi->bw_time_stamp;
|
||||
unsigned long dirtied;
|
||||
unsigned long written;
|
||||
|
||||
/*
|
||||
@@ -610,6 +900,7 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi,
|
||||
if (elapsed < BANDWIDTH_INTERVAL)
|
||||
return;
|
||||
|
||||
dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
|
||||
written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
|
||||
|
||||
/*
|
||||
@@ -619,18 +910,23 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi,
|
||||
if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
|
||||
goto snapshot;
|
||||
|
||||
if (thresh)
|
||||
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,
|
||||
@@ -639,37 +935,99 @@ static void bdi_update_bandwidth(struct backing_dev_info *bdi,
|
||||
if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
|
||||
return;
|
||||
spin_lock(&bdi->wb.list_lock);
|
||||
__bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
|
||||
start_time);
|
||||
__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.
|
||||
*/
|
||||
if (bdi_dirty)
|
||||
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 perform writeback if the system is over `vm_dirty_ratio'.
|
||||
* 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 write_chunk)
|
||||
unsigned long pages_dirtied)
|
||||
{
|
||||
unsigned long nr_reclaimable, bdi_nr_reclaimable;
|
||||
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;
|
||||
unsigned long task_bdi_thresh;
|
||||
unsigned long min_task_bdi_thresh;
|
||||
unsigned long pages_written = 0;
|
||||
unsigned long pause = 1;
|
||||
long pause = 0;
|
||||
long uninitialized_var(max_pause);
|
||||
bool dirty_exceeded = false;
|
||||
bool clear_dirty_exceeded = true;
|
||||
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);
|
||||
@@ -681,12 +1039,28 @@ static void balance_dirty_pages(struct address_space *mapping,
|
||||
* catch-up. This avoids (excessively) small writeouts
|
||||
* when the bdi limits are ramping up.
|
||||
*/
|
||||
if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
|
||||
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);
|
||||
min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
|
||||
task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
|
||||
|
||||
/*
|
||||
* In order to avoid the stacked BDI deadlock we need
|
||||
@@ -698,56 +1072,69 @@ static void balance_dirty_pages(struct address_space *mapping,
|
||||
* actually dirty; with m+n sitting in the percpu
|
||||
* deltas.
|
||||
*/
|
||||
if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
|
||||
bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
|
||||
bdi_dirty = bdi_nr_reclaimable +
|
||||
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_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
|
||||
bdi_dirty = bdi_nr_reclaimable +
|
||||
bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
|
||||
bdi_dirty = bdi_reclaimable +
|
||||
bdi_stat(bdi, BDI_WRITEBACK);
|
||||
}
|
||||
|
||||
/*
|
||||
* The bdi thresh is somehow "soft" limit derived from the
|
||||
* global "hard" limit. The former helps to prevent heavy IO
|
||||
* bdi or process from holding back light ones; The latter is
|
||||
* the last resort safeguard.
|
||||
*/
|
||||
dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
|
||||
dirty_exceeded = (bdi_dirty > bdi_thresh) ||
|
||||
(nr_dirty > dirty_thresh);
|
||||
clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
|
||||
(nr_dirty <= dirty_thresh);
|
||||
|
||||
if (!dirty_exceeded)
|
||||
break;
|
||||
|
||||
if (!bdi->dirty_exceeded)
|
||||
if (dirty_exceeded && !bdi->dirty_exceeded)
|
||||
bdi->dirty_exceeded = 1;
|
||||
|
||||
bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
|
||||
bdi_thresh, bdi_dirty, start_time);
|
||||
bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
|
||||
nr_dirty, bdi_thresh, bdi_dirty,
|
||||
start_time);
|
||||
|
||||
/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
|
||||
* Unstable writes are a feature of certain networked
|
||||
* filesystems (i.e. NFS) in which data may have been
|
||||
* written to the server's write cache, but has not yet
|
||||
* been flushed to permanent storage.
|
||||
* Only move pages to writeback if this bdi is over its
|
||||
* threshold otherwise wait until the disk writes catch
|
||||
* up.
|
||||
*/
|
||||
trace_balance_dirty_start(bdi);
|
||||
if (bdi_nr_reclaimable > task_bdi_thresh) {
|
||||
pages_written += writeback_inodes_wb(&bdi->wb,
|
||||
write_chunk);
|
||||
trace_balance_dirty_written(bdi, pages_written);
|
||||
if (pages_written >= write_chunk)
|
||||
break; /* We've done our duty */
|
||||
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);
|
||||
if (unlikely(pos_ratio == 0)) {
|
||||
pause = max_pause;
|
||||
goto pause;
|
||||
}
|
||||
task_ratelimit = (u64)dirty_ratelimit *
|
||||
pos_ratio >> RATELIMIT_CALC_SHIFT;
|
||||
pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
|
||||
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_UNINTERRUPTIBLE);
|
||||
io_schedule_timeout(pause);
|
||||
trace_balance_dirty_wait(bdi);
|
||||
|
||||
dirty_thresh = hard_dirty_limit(dirty_thresh);
|
||||
/*
|
||||
@@ -756,24 +1143,30 @@ static void balance_dirty_pages(struct address_space *mapping,
|
||||
* 200ms is typically more than enough to curb heavy dirtiers;
|
||||
* (b) the pause time limit makes the dirtiers more responsive.
|
||||
*/
|
||||
if (nr_dirty < dirty_thresh &&
|
||||
bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 &&
|
||||
time_after(jiffies, start_time + MAX_PAUSE))
|
||||
if (nr_dirty < dirty_thresh)
|
||||
break;
|
||||
|
||||
/*
|
||||
* Increase the delay for each loop, up to our previous
|
||||
* default of taking a 100ms nap.
|
||||
*/
|
||||
pause <<= 1;
|
||||
if (pause > HZ / 10)
|
||||
pause = HZ / 10;
|
||||
}
|
||||
|
||||
/* Clear dirty_exceeded flag only when no task can exceed the limit */
|
||||
if (clear_dirty_exceeded && bdi->dirty_exceeded)
|
||||
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;
|
||||
|
||||
@@ -785,8 +1178,10 @@ static void balance_dirty_pages(struct address_space *mapping,
|
||||
* In normal mode, we start background writeout at the lower
|
||||
* background_thresh, to keep the amount of dirty memory low.
|
||||
*/
|
||||
if ((laptop_mode && pages_written) ||
|
||||
(!laptop_mode && (nr_reclaimable > background_thresh)))
|
||||
if (laptop_mode)
|
||||
return;
|
||||
|
||||
if (nr_reclaimable > background_thresh)
|
||||
bdi_start_background_writeback(bdi);
|
||||
}
|
||||
|
||||
@@ -800,7 +1195,7 @@ void set_page_dirty_balance(struct page *page, int page_mkwrite)
|
||||
}
|
||||
}
|
||||
|
||||
static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
|
||||
static DEFINE_PER_CPU(int, bdp_ratelimits);
|
||||
|
||||
/**
|
||||
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
|
||||
@@ -820,31 +1215,39 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
|
||||
unsigned long nr_pages_dirtied)
|
||||
{
|
||||
struct backing_dev_info *bdi = mapping->backing_dev_info;
|
||||
unsigned long ratelimit;
|
||||
unsigned long *p;
|
||||
int ratelimit;
|
||||
int *p;
|
||||
|
||||
if (!bdi_cap_account_dirty(bdi))
|
||||
return;
|
||||
|
||||
ratelimit = ratelimit_pages;
|
||||
if (mapping->backing_dev_info->dirty_exceeded)
|
||||
ratelimit = 8;
|
||||
ratelimit = current->nr_dirtied_pause;
|
||||
if (bdi->dirty_exceeded)
|
||||
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
|
||||
|
||||
current->nr_dirtied += nr_pages_dirtied;
|
||||
|
||||
/*
|
||||
* Check the rate limiting. Also, we do not want to throttle real-time
|
||||
* tasks in balance_dirty_pages(). Period.
|
||||
*/
|
||||
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);
|
||||
*p += nr_pages_dirtied;
|
||||
if (unlikely(*p >= ratelimit)) {
|
||||
ratelimit = sync_writeback_pages(*p);
|
||||
if (unlikely(current->nr_dirtied >= ratelimit))
|
||||
*p = 0;
|
||||
preempt_enable();
|
||||
balance_dirty_pages(mapping, ratelimit);
|
||||
return;
|
||||
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);
|
||||
|
||||
@@ -900,7 +1303,8 @@ void laptop_mode_timer_fn(unsigned long data)
|
||||
* threshold
|
||||
*/
|
||||
if (bdi_has_dirty_io(&q->backing_dev_info))
|
||||
bdi_start_writeback(&q->backing_dev_info, nr_pages);
|
||||
bdi_start_writeback(&q->backing_dev_info, nr_pages,
|
||||
WB_REASON_LAPTOP_TIMER);
|
||||
}
|
||||
|
||||
/*
|
||||
@@ -939,22 +1343,17 @@ void laptop_sync_completion(void)
|
||||
*
|
||||
* Here we set ratelimit_pages to a level which ensures that when all CPUs are
|
||||
* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
|
||||
* thresholds before writeback cuts in.
|
||||
*
|
||||
* But the limit should not be set too high. Because it also controls the
|
||||
* amount of memory which the balance_dirty_pages() caller has to write back.
|
||||
* If this is too large then the caller will block on the IO queue all the
|
||||
* time. So limit it to four megabytes - the balance_dirty_pages() caller
|
||||
* will write six megabyte chunks, max.
|
||||
* thresholds.
|
||||
*/
|
||||
|
||||
void writeback_set_ratelimit(void)
|
||||
{
|
||||
ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
|
||||
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;
|
||||
if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
|
||||
ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
|
||||
}
|
||||
|
||||
static int __cpuinit
|
||||
@@ -1324,6 +1723,7 @@ void account_page_dirtied(struct page *page, struct address_space *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_dirty_inc(current);
|
||||
task_io_account_write(PAGE_CACHE_SIZE);
|
||||
}
|
||||
|
||||
Reference in New Issue
Block a user