writeback: avoid unnecessary calculation of bdi dirty thresholds
Split get_dirty_limits() into global_dirty_limits()+bdi_dirty_limit(), so
that the latter can be avoided when under global dirty background
threshold (which is the normal state for most systems).
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2cf69a5..1ea13ef 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -267,10 +267,11 @@
*
* dirty -= (dirty/8) * p_{t}
*/
-static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty)
+static unsigned long task_dirty_limit(struct task_struct *tsk,
+ unsigned long bdi_dirty)
{
long numerator, denominator;
- unsigned long dirty = *pdirty;
+ unsigned long dirty = bdi_dirty;
u64 inv = dirty >> 3;
task_dirties_fraction(tsk, &numerator, &denominator);
@@ -278,10 +279,8 @@
do_div(inv, denominator);
dirty -= inv;
- if (dirty < *pdirty/2)
- dirty = *pdirty/2;
- *pdirty = dirty;
+ return max(dirty, bdi_dirty/2);
}
/*
@@ -391,9 +390,7 @@
return x + 1; /* Ensure that we never return 0 */
}
-void
-get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
- unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
+void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
{
unsigned long background;
unsigned long dirty;
@@ -425,26 +422,28 @@
}
*pbackground = background;
*pdirty = dirty;
+}
- if (bdi) {
- u64 bdi_dirty;
- long numerator, denominator;
+unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
+ unsigned long dirty)
+{
+ u64 bdi_dirty;
+ long numerator, denominator;
- /*
- * Calculate this BDI's share of the dirty ratio.
- */
- bdi_writeout_fraction(bdi, &numerator, &denominator);
+ /*
+ * Calculate this BDI's share of the dirty ratio.
+ */
+ bdi_writeout_fraction(bdi, &numerator, &denominator);
- bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
- bdi_dirty *= numerator;
- do_div(bdi_dirty, denominator);
- bdi_dirty += (dirty * bdi->min_ratio) / 100;
- if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
- bdi_dirty = dirty * bdi->max_ratio / 100;
+ bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
+ bdi_dirty *= numerator;
+ do_div(bdi_dirty, denominator);
- *pbdi_dirty = bdi_dirty;
- task_dirty_limit(current, pbdi_dirty);
- }
+ bdi_dirty += (dirty * bdi->min_ratio) / 100;
+ if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
+ bdi_dirty = dirty * bdi->max_ratio / 100;
+
+ return bdi_dirty;
}
/*
@@ -475,13 +474,24 @@
.range_cyclic = 1,
};
- get_dirty_limits(&background_thresh, &dirty_thresh,
- &bdi_thresh, bdi);
-
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
nr_writeback = global_page_state(NR_WRITEBACK);
+ global_dirty_limits(&background_thresh, &dirty_thresh);
+
+ /*
+ * Throttle it only when the background writeback cannot
+ * catch-up. This avoids (excessively) small writeouts
+ * when the bdi limits are ramping up.
+ */
+ if (nr_reclaimable + nr_writeback <
+ (background_thresh + dirty_thresh) / 2)
+ break;
+
+ bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
+ bdi_thresh = task_dirty_limit(current, bdi_thresh);
+
/*
* In order to avoid the stacked BDI deadlock we need
* to ensure we accurately count the 'dirty' pages when
@@ -513,15 +523,6 @@
if (!dirty_exceeded)
break;
- /*
- * Throttle it only when the background writeback cannot
- * catch-up. This avoids (excessively) small writeouts
- * when the bdi limits are ramping up.
- */
- if (nr_reclaimable + nr_writeback <
- (background_thresh + dirty_thresh) / 2)
- break;
-
if (!bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
@@ -634,7 +635,7 @@
unsigned long dirty_thresh;
for ( ; ; ) {
- get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
+ global_dirty_limits(&background_thresh, &dirty_thresh);
/*
* Boost the allowable dirty threshold a bit for page