+ writeback-add-comment-to-the-dirty-limit-functions.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     writeback: add comment to the dirty limit functions
has been added to the -mm tree.  Its filename is
     writeback-add-comment-to-the-dirty-limit-functions.patch

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------------------------------------------------------
Subject: writeback: add comment to the dirty limit functions
From: Wu Fengguang <fengguang.wu@intel.com>

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>
---

 mm/page-writeback.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff -puN mm/page-writeback.c~writeback-add-comment-to-the-dirty-limit-functions mm/page-writeback.c
--- a/mm/page-writeback.c~writeback-add-comment-to-the-dirty-limit-functions
+++ a/mm/page-writeback.c
@@ -390,6 +390,15 @@ 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 +433,18 @@ void global_dirty_limits(unsigned long *
 	*pdirty = dirty;
 }
 
-unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
-			       unsigned long dirty)
+/**
+ * bdi_dirty_limit - current task's share of dirty throttling threshold on @bdi
+ *
+ * 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.
+ */
+unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
 {
 	u64 bdi_dirty;
 	long numerator, denominator;
_

Patches currently in -mm which might be from fengguang.wu@intel.com are

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-avoid-unnecessary-calculation-of-bdi-dirty-thresholds.patch
writeback-avoid-unnecessary-calculation-of-bdi-dirty-thresholds-fix.patch
writeback-add-comment-to-the-dirty-limit-functions.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