writeback: add comment to the dirty limits functions
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From: Peter Zijlstra on 6 Aug 2010 06:20 On Fri, 2010-08-06 at 00:10 +0800, Wu Fengguang wrote: Acked-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> > +/** > + * 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. > + */ Another thing solved by the introduction of per-bdi dirty limits (and now per-bdi flushing) is the whole stacked-bdi writeout deadlock. Although I'm not sure we want/need to mention that here. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Wu Fengguang on 7 Aug 2010 12:50
On Fri, Aug 06, 2010 at 06:17:26PM +0800, Peter Zijlstra wrote: > On Fri, 2010-08-06 at 00:10 +0800, Wu Fengguang wrote: > > Acked-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> > > > +/** > > + * 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. > > + */ > > Another thing solved by the introduction of per-bdi dirty limits (and > now per-bdi flushing) is the whole stacked-bdi writeout deadlock. > > Although I'm not sure we want/need to mention that here. The changelog looks like a suitable place :) Thanks, Fengguang --- Subject: writeback: add comment to the dirty limits functions From: Wu Fengguang <fengguang.wu(a)intel.com> Date: Thu Jul 15 09:54:25 CST 2010 Document global_dirty_limits(), bdi_dirty_limit() and task_dirty_limit(). Note that another thing solved by the introduction of per-bdi dirty limits (and now per-bdi flushing) is the whole stacked-bdi writeout deadlock. -- Peter Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Dave Chinner <david(a)fromorbit.com> Cc: Jens Axboe <axboe(a)kernel.dk> Acked-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> --- mm/page-writeback.c | 31 ++++++++++++++++++++++++++++--- 1 file changed, 28 insertions(+), 3 deletions(-) --- linux-next.orig/mm/page-writeback.c 2010-08-03 23:14:19.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-08-05 00:37:17.000000000 +0800 @@ -261,11 +261,18 @@ static inline void task_dirties_fraction } /* - * 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 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 * *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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |