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author | Wu Fengguang <fengguang.wu@intel.com> | 2010-08-11 14:17:40 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-08-12 08:43:30 -0700 |
commit | 1babe18385d3976043c04237ce837f3736197eb4 (patch) | |
tree | c766bb0022ec5188cd7e991fc1f9ad51687e8aca | |
parent | 16c4042f08919f447d6b2a55679546c9b97c7264 (diff) | |
download | op-kernel-dev-1babe18385d3976043c04237ce837f3736197eb4.zip op-kernel-dev-1babe18385d3976043c04237ce837f3736197eb4.tar.gz |
writeback: add comment to the dirty limit functions
Document global_dirty_limits() and bdi_dirty_limit().
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-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 1ea13ef..20890d8 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; |