mm: dirty balancing for tasks

Based on ideas of Andrew:
  http://marc.info/?l=linux-kernel&m=102912915020543&w=2

Scale the bdi dirty limit inversly with the tasks dirty rate.
This makes heavy writers have a lower dirty limit than the occasional writer.

Andrea proposed something similar:
  http://lwn.net/Articles/152277/

The main disadvantage to his patch is that he uses an unrelated quantity to
measure time, which leaves him with a workload dependant tunable. Other than
that the two approaches appear quite similar.

[akpm@linux-foundation.org: fix warning]
Signed-off-by: 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>

1 files changed, 49 insertions, 1 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b0360546ac86..4073d531cd7b 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -118,6 +118,7 @@ static void background_writeout(unsigned long _min_pages);
  *
  */
 static struct prop_descriptor vm_completions;
+static struct prop_descriptor vm_dirties;
 
 static unsigned long determine_dirtyable_memory(void);
 
@@ -146,6 +147,7 @@ int dirty_ratio_handler(struct ctl_table *table, int write,
         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
                 int shift = calc_period_shift();
                 prop_change_shift(&vm_completions, shift);
+                prop_change_shift(&vm_dirties, shift);
         }
         return ret;
 }
@@ -159,6 +161,11 @@ static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
         __prop_inc_percpu(&vm_completions, &bdi->completions);
 }
 
+static inline void task_dirty_inc(struct task_struct *tsk)
+{
+        prop_inc_single(&vm_dirties, &tsk->dirties);
+}
+
 /*
  * Obtain an accurate fraction of the BDI's portion.
  */
@@ -198,6 +205,37 @@ clip_bdi_dirty_limit(struct backing_dev_info *bdi, long dirty, long *pbdi_dirty)
         *pbdi_dirty = min(*pbdi_dirty, avail_dirty);
 }
 
+static inline void task_dirties_fraction(struct task_struct *tsk,
+                long *numerator, long *denominator)
+{
+        prop_fraction_single(&vm_dirties, &tsk->dirties,
+                                numerator, denominator);
+}
+
+/*
+ * scale the dirty limit
+ *
+ * task specific dirty limit:
+ *
+ *   dirty -= (dirty/8) * p_{t}
+ */
+void task_dirty_limit(struct task_struct *tsk, long *pdirty)
+{
+        long numerator, denominator;
+        long dirty = *pdirty;
+        u64 inv = dirty >> 3;
+
+        task_dirties_fraction(tsk, &numerator, &denominator);
+        inv *= numerator;
+        do_div(inv, denominator);
+
+        dirty -= inv;
+        if (dirty < *pdirty/2)
+                dirty = *pdirty/2;
+
+        *pdirty = dirty;
+}
+
 /*
  * Work out the current dirty-memory clamping and background writeout
  * thresholds.
@@ -304,6 +342,7 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
 
                 *pbdi_dirty = bdi_dirty;
                 clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
+                task_dirty_limit(current, pbdi_dirty);
         }
 }
 
@@ -720,6 +759,7 @@ void __init page_writeback_init(void)
 
         shift = calc_period_shift();
         prop_descriptor_init(&vm_completions, shift);
+        prop_descriptor_init(&vm_dirties, shift);
 }
 
 /**
@@ -998,7 +1038,7 @@ EXPORT_SYMBOL(redirty_page_for_writepage);
  * If the mapping doesn't provide a set_page_dirty a_op, then
  * just fall through and assume that it wants buffer_heads.
  */
-int fastcall set_page_dirty(struct page *page)
+static int __set_page_dirty(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
 
@@ -1016,6 +1056,14 @@ int fastcall set_page_dirty(struct page *page)
         }
         return 0;
 }
+
+int fastcall set_page_dirty(struct page *page)
+{
+        int ret = __set_page_dirty(page);
+        if (ret)
+                task_dirty_inc(current);
+        return ret;
+}
 EXPORT_SYMBOL(set_page_dirty);
 
 /*