diff options
| -rw-r--r-- | mm/page-writeback.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 1ea13ef350a8..20890d80c7ef 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -261,11 +261,18 @@ static inline void task_dirties_fraction(struct task_struct *tsk, } /* - * scale the dirty limit + * task_dirty_limit - scale down dirty throttling threshold for one task * * task specific dirty limit: * * dirty -= (dirty/8) * p_{t} + * + * To protect light/slow dirtying tasks from heavier/fast ones, we start + * throttling individual tasks before reaching the bdi dirty limit. + * Relatively low thresholds will be allocated to heavy dirtiers. So when + * dirty pages grow large, heavy dirtiers will be throttled first, which will + * effectively curb the growth of dirty pages. Light dirtiers with high enough + * dirty threshold may never get throttled. */ static unsigned long task_dirty_limit(struct task_struct *tsk, unsigned long bdi_dirty) @@ -390,6 +397,15 @@ unsigned long determine_dirtyable_memory(void) 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 + * runtime tasks. + */ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) { unsigned long background; @@ -424,8 +440,17 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) *pdirty = dirty; } -unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, - unsigned long dirty) +/** + * bdi_dirty_limit - @bdi's share of dirty throttling threshold + * + * Allocate 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; |