The patch titled
writeback-add-comment-to-the-dirty-limit-functions-update
has been added to the -mm tree. Its filename is
writeback-add-comment-to-the-dirty-limit-functions-update.patch
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------------------------------------------------------
Subject: writeback-add-comment-to-the-dirty-limit-functions-update
From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Document global_dirty_limits(), bdi_dirty_limit() and task_dirty_limit().
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff -puN mm/page-writeback.c~writeback-add-comment-to-the-dirty-limit-functions-update mm/page-writeback.c
--- a/mm/page-writeback.c~writeback-add-comment-to-the-dirty-limit-functions-update
+++ a/mm/page-writeback.c
@@ -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)
@@ -391,7 +398,7 @@ unsigned long determine_dirtyable_memory
}
/**
- * global_dirty_limits - background writeback and dirty throttling thresholds
+ * 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
@@ -434,15 +441,14 @@ void global_dirty_limits(unsigned long *
}
/**
- * bdi_dirty_limit - current task's share of dirty throttling threshold on @bdi
+ * 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
*
- * Once the global dirty limit is _exceeded_, all dirtiers will be throttled.
- * To avoid starving fast devices (which can sync dirty pages in short time) or
- * throttling light dirtiers, we start throttling individual tasks on a per-bdi
- * basis when _approaching_ the global dirty limit. Relative high limits will
- * be allocated to fast devices and/or light dirtiers. The bdi's dirty share is
- * evaluated adapting to its throughput and bounded if the bdi->min_ratio
- * and/or bdi->max_ratio parameters are set.
+ * 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)
{
_
Patches currently in -mm which might be from fengguang.wu@xxxxxxxxx are
origin.patch
linux-next.patch
fs-inodec-work-around-bug.patch
include-linux-fsh-complete-hexification-of-fmode_-constants.patch
vfs-o_-bit-numbers-uniqueness-check.patch
vfs-introduce-fmode_neg_offset-for-allowing-negative-f_pos.patch
writeback-reduce-calls-to-global_page_state-in-balance_dirty_pages.patch
writeback-reduce-calls-to-global_page_state-in-balance_dirty_pages-update.patch
writeback-avoid-unnecessary-calculation-of-bdi-dirty-thresholds.patch
writeback-avoid-unnecessary-calculation-of-bdi-dirty-thresholds-update.patch
writeback-add-comment-to-the-dirty-limit-functions.patch
writeback-add-comment-to-the-dirty-limit-functions-update.patch
writeback-dont-redirty-tail-an-inode-with-dirty-pages.patch
writeback-fix-queue_io-ordering.patch
writeback-merge-for_kupdate-and-for_kupdate-cases.patch
vfs-add-super-operation-writeback_inodes.patch
--
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